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BZYCT-137: Genetics and Evolutionary Biology

BZYCT-137: Genetics and Evolutionary Biology

IGNOU Solved Assignment Solution for 2023

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Assignment Solution

Assignment Code: BZYCT-137/TMA/2023

Course Code: BZYCT-137

Assignment Name: Genetics And Evolutionary Biology

Year: 2023

Verification Status: Verified by Professor

 

Note: Attempt all questions. The marks for each question are indicated against it.

 


Part-A


 

Q1i) How is co-dominance different from incomplete dominance? (5)

Ans) Co-dominance and incomplete dominance are two ways to describe how alleles of a gene work together in heterozygous people. Both ways of passing on traits result in phenotypes that are halfway between those of homozygous dominant and homozygous recessive people. However, there are major differences between them.

 

When a heterozygote has a phenotype that is in between the two phenotypes of a homozygote, this is called incomplete dominance. In other words, the traits of the heterozygous child are a mix of those of the two homozygous parents. For example, if a snapdragon plant with red flowers is crossed with a snapdragon plant with white flowers, the result is a heterozygous plant with pink flowers. The red and white flowers were mixed to make the pink flowers. This is because the allele for red flowers is not completely dominant over the allele for white flowers. As a result, the phenotype is a mix of the two.

 

On the other hand, co-dominance happens when both alleles of a gene are expressed in a heterozygous person, but neither allele is dominant or recessive. In other words, both traits show up at the same time without mixing or taking over. Blood groups are a great example of how co-dominance works. The gene that controls blood type has three copies, or alleles: A, B, and O. The A and B alleles are both dominant. The O allele, on the other hand, is weaker. So, a person with the AB blood group has both A and B antigens on their red blood cells, while a person with the O blood group has neither A nor B antigens.

 

The roan coat colour of cattle is another case of co-dominance. Instead of a mix of pink hairs, a roan cow's coat has both red and white hairs. This is because the heterozygous person has both the red and white alleles of the gene for coat colour.


Q1ii) Explain the phenomenon of masking the expression of gene by another in epitasis. (5)

Ans) Epistasis is when the way one gene is expressed is affected by the way another gene is expressed. The way a trait shows up is controlled by how different genes work together. Sometimes, one gene can hide or stop another gene from being expressed. This can cause the phenotype to be different from what would be expected based on the genotype.

 

Masking happens when the presence of one gene stops another gene from being turned on. This kind of epistasis is also called dominant epistasis. In masking, the gene that does the hiding is called the epistatic gene, and the gene that is hidden is called the hypostatic gene. Both the dominant and recessive forms of the epistatic gene and the hypostatic gene are possible.

 

The interaction between two genes that control the colour of a mouse's coat is the simplest example of masking. In this case, one gene oversees making black pigment and another gene oversees making brown pigment. The black pigment gene is stronger than the brown pigment gene. But a third gene controls the whole process of making pigment. If this third gene is homozygous recessive, the mice won't make any pigment and will be albino. In this case, the third gene influences the genes that control the production of pigment. If a mouse has the dominant allele for black pigment but is homozygous recessive for the third gene, it will be albino because the gene for making pigment is covered up.

 

Another example of masking is how the genes that control the colour of a snapdragon's flower work together. In this case, the colour is controlled by two genes: one for the red pigment and one for the white pigment. The red pigment gene is stronger than the white pigment gene. But a third gene controls whether the colour is made in the petals. If both copies of this gene are recessive, then no pigment is made, and the flowers are white. In this case, the third gene influences the genes that control the production of pigment. If a snapdragon has the dominant allele for red pigment but is homozygous recessive for the third gene, it won't make any pigment and will have white flowers.

 

Q2i) In Drosophila, the recessive, sex-linked genes abnormal eyes facet (fa) and singed bristles (sn) show 18 percent recombination. (5)

 

a) If a singed male is crossed to a fa+/fa+ female, what phenotypes are expected in the F1?

Ans) To solve this problem, we need to first understand the concept of recombination and sex-linkage in Drosophila genetics.

 

Recombination occurs when the two genes are located on different chromosomes or far apart on the same chromosome. In Drosophila, the sex chromosomes X and Y are responsible for determining the sex of an individual. Since males have only one X chromosome, any recessive allele on the X chromosome will be expressed. This has sex-linked inheritance different from autosomal inheritance, where both males and females have two copies of each chromosome.

 

In this problem, we are given that the genes fa and sn are recessive and sex-linked, and they show 18% recombination. This means that the two genes are located on the same chromosome, but not very close together. The distance between the genes is estimated using the percentage of recombinant offspring in a cross. In this case, 18% of the offspring show recombination between fa and sn, which means that the two genes are about 18 map units apart on the X chromosome.

 

Now, let's consider the cross between a singed male (snY) and a fa+/fa+ female (fa+X fa+X). Since the singed gene is recessive and sex-linked, the genotype of the male can be written as snY. The female is heterozygous for the fa gene, which means her genotype can be written as fa+X faX.

The first step is to write out the gametes that each parent can produce. The male can produce only one type of gamete, which is snY. The female can produce two types of gametes, fa+X and faX.

The next step is to combine the gametes and determine the genotypes and phenotypes of the offspring. We can use a Punnett square to do this.

 

The Punnett square shows that all the male offspring will be singed (snY), since they inherit the singed gene from their father. The female offspring can be either singed or wild type, depending on their genotype.

 

Therefore, the expected phenotypes in the F1 are:

  1. All male offspring will be singed (snY).

  2. All female offspring will be either singed (fa+X snY) or wild type (faX snY), with equal probability.

 

b) If the F1 males and females are inbred what phenotypic proportions would be expected to occur in F2 males and females?

Ans) If the F1 males and females produced from the cross between a singed male and a fa+/fa+ female is inbred, the expected phenotypic proportions in the F2 generation will depend on the genotypes of the F1 individuals.

 

The F1 male is singed (snY) and has normal eyes (fa+Y). The F1 female is heterozygous for both genes, i.e., she has singed bristles (snX) and normal eyes (fa+X).

The F1 male and female can produce four types of gametes each:

 

snY and fa+X

snY and snX

fa+Y and fa+X

fa+Y and snX

 

Therefore, the possible genotypes and phenotypes in the F2 generation can be predicted by using a Punnett square. The genotypes and their frequencies are shown below:

 


The expected phenotypic ratios are:

Singed, normal eyes: 1/4 (snYfa+X and snXfa+X)

Singed, abnormal eyes: 1/4 (snYsnX and snXsnX)

Normal bristles, normal eyes: 1/4 (fa+Yfa+X and fa+Xfa+X)

Normal bristles, abnormal eyes: 1/4 (fa+YsnX and fa+XsnX)

 

Therefore, in the F2 generation, we would expect to see a 1:1 ratio of singed and normal-bristled flies, and a 1:1 ratio of normal and abnormal-eyed flies, regardless of their sex.

 

Q2ii) Two recessive genes ds and mp are present in corn. These are linked and are 20 map units apart. From the cross: (5)

dsmp/++ x ds+/+mp

What percentage of the progeny would be expected to be both ds and mp in the phenotype?

Ans) The given cross is between dsmp/++ and ds+/+mp individuals. Here, ds and mp are recessive genes, and ++ represents the dominant alleles for both the genes.

 

The parental genotypes are:

 

dsmp/++ x ds+/+mp

 

The slash (/) represents the phase of the alleles, i.e., the chromosome from which each allele is derived.

 

dsmp/++ will produce two types of gametes:

dsmp and ++

ds+/+mp will produce two types of gametes:

ds+ and +mp

 

The + symbol represents the dominant allele, and the absence of a symbol represents the recessive allele.

 

Now, let us write down the possible genotypes and phenotypes of the offspring:

dsmp/ds+ dsmp/+mp ds+/+ ++/++ ds+/++ +mp/++

dsmp/ds+ and dsmp/+mp have both the recessive alleles and will express the recessive phenotype.

 

Thus, the offspring with these genotypes will show both ds and mp in the phenotype.

ds+/+ and ++/++ have at least one dominant allele and will show the dominant phenotype.

ds+/++ and +mp/++ have one recessive allele each and will show the dominant phenotype.

Let us now calculate the percentage of offspring that will have both ds and mp in the phenotype:

Since ds and mp are 20 map units apart, they have a recombination frequency of 20%.

 

This means that out of 100 gametes produced, 20 gametes will be recombinant (ds+ and +mp) and 80 gametes will be non-recombinant (dsmp and ++).

 

The non-recombinant gametes will form the parental types, i.e., dsmp/++ and ds+/+mp.

The recombinant gametes will form the non-parental types, i.e., ds+ and +mp.

 

Now, let us write down the possible genotypes and phenotypes of the offspring and their expected frequencies.

dsmp/ds+ - both ds and mp will be expressed - 20% (recombinant)

dsmp/+mp - both ds and mp will be expressed - 20% (recombinant)

ds+/+ - neither ds nor mp will be expressed - 40% (non-recombinant)

++/++ - neither ds nor mp will be expressed - 40% (non-recombinant)

ds+/++ - neither ds nor mp will be expressed - 10% (recombinant)

+mp/++ - neither ds nor mp will be expressed - 10% (recombinant)

 

Thus, the expected percentage of offspring that will have both ds and mp in the phenotype is 20% + 20% = 40%.

 

Therefore, in the given cross, 40% of the progeny would be expected to be both ds and mp in the phenotype.

 

Q3a) In the following statements choose the alternate correct word given in parenthesis. (7)

 

i) The DNA regions in chloroplast could be observed under (light microscope/electron microscope).

Ans) The DNA regions in chloroplast could be observed under electron microscope.

 

ii) The regions containing cpDNA are called (nucleoids/celluloids).

Ans) The regions containing cpDNA are called nucleoids.

 

iii) Each nucleoid contains (a single/a few) copies of DNA.

Ans) Each nucleoid contains a few copies of DNA.

 

iv) The cpDNA and mtDNA are usually (circular/linear) in nature.

Ans) The cpDNA and mtDNA are usually circular in nature.

 

v) Both chloroplast and mitochondria contain (a few/many) copies of DNA.

Ans) Both chloroplast and mitochondria contain many copies of DNA.

 

vi) The mtDNA of yeast is (bigger/smaller) than mtDNA of humans.

Ans) The mtDNA of yeast is smaller than mtDNA of humans.

 

vii) The occurrence of introns is discovered in (yeast/human).

Ans) The occurrence of introns is discovered in humans.

 

Q3b) Which among the following statements are correct? (3)

i) Mitochondria contain 80 S ribosomes.

Ans) False.

 

ii) The mRNA encoded by nuclear genes for the smaller subunit of rubisco is translated in the chloroplast.

Ans) False.

 

iii) The inheritance of chloroplast genome is independent of nuclear genome.

Ans) False.

 

Q4i) Explain why sterility is common in polyploid organisms? (5)

Ans) Polyploidy is when an organism's genome contains more than two complete sets of chromosomes. Polyploid organisms can form in several ways, such as when chromosomes don't split during cell division (called "non-disjunction") or when two gametes with an extra set of chromosomes join. Polyploid organisms can be found in many different types of plants and animals, but they aren't very common in humans and other mammals. In polyploid organisms, sterility, or the inability to make healthy offspring, is a common trait.

 

The exact ways that polyploid organisms become sterile are not well understood and are likely to be complicated. One possible reason is that having more than one set of chromosomes causes an imbalance in how genes are expressed, which messes up the way important biological processes work. For example, genes involved in meiosis and making gametes can be messed up, causing the body to make gametes that don't work. Also, having more than one set of chromosomes can change how genes are turned on and off, causing abnormal proteins to be made and cellular dysfunction.

 

Another thing that could cause polyploid sterility is problems with how chromosomes pair up and split up during meiosis. During meiosis, homologous chromosomes pair up and then split in organisms that are diploid. This makes haploid gametes. But in polyploid organisms, it can be hard for homologous chromosomes to pair up and split up. This can cause the gametes to be out of balance, making it impossible for them to grow into healthy babies. Also, when meiosis happens in polyploid organisms, chromosomes can form multivalent, which are groups of more than two identical chromosomes. This can lead to mistakes in how chromosomes are split up.

 

Polyploidy can also change the size, shape, and number of the cells. Most of the time, polyploid cells are bigger than diploid cells, and their structure and function may be different. These differences can cause problems with the growth of tissues and the separation of cells, which can lead to sterility. Polyploidy can also make it hard for cells to divide, which can lead to the growth of cells with an abnormal number of chromosomes.

 

Q4ii) What is trisomy? By what mechanisms does it come into existence? (5)

Ans) Trisomy is a genetic condition in which a person has three copies of a chromosome instead of the usual two. Trisomy can happen in any chromosome, but it most often happens in chromosome 21, which causes Down syndrome.

 

Different things can cause trisomy, such as non-disjunction, translocation, and mosaicism.

Non-disjunction happens when sister chromatids or homologous chromosomes do not separate properly when a cell divides. Because of this, one of the daughter cells has an extra chromosome and the other is missing a chromosome. During fertilisation, if a sperm or egg has an extra chromosome, it can cause a zygote to have trisomy.

 

Trisomy can also happen because of translocation. Translocation is when a piece of one chromosome is moved to another. It can happen when meiosis goes wrong or when cells are exposed to chemicals or radiation. Trisomy happens when a piece of a chromosome with a gene is moved to another chromosome. This can make the gene have three copies instead of the usual two copies.

 

Mosaicism is the third way that trisomy can happen. Mosaicism happens when a person has two or more groups of cells that have different genes. In mosaicism, some cells have three copies of a gene, but not all. During embryonic development, this can happen when a mutation happens in one cell but not in others. The person may have some normal cells and some trisomic cells as a result.

 

Trisomy can hurt a person's health and development in a lot of ways. The severity of the condition depends on which chromosome is affected and how much of that chromosome is duplicated. Most of the time, trisomy leads to problems with development and intelligence. In some cases, it can also cause physical problems, like problems with the heart or the face.


Q5i) Define mutation. Explain the following types of mutations briefly: (5)

 

(a) Induced mutations

(b) Suppressor mutations

Ans) Mutation is when the order of the DNA in an organism's genome changes. It can happen on its own or because of exposure to chemicals, radiation, or viruses, among other things. Depending on where they happen and what kind they are, mutations can have no effect, good effects, or bad effects. Different kinds of mutations can be grouped together based on how they change the genome.

 

Induced Mutations: Mutations that happen because of something from the outside, like mutagens, are called "induced mutations." Mutagens are things that can change the DNA sequence. They can be physical, chemical, or biological. Ionizing radiation, ultraviolet radiation, and X-rays are all types of physical mutagens. Chemicals like alkylating agents, base analogy agents, and intercalating agents can cause mutations. Biological mutagens include viruses and transposable elements.

Induced mutations can happen in different ways, such as when a base is changed, deleted, added, or moved. The type and number of mutations caused by a mutagen depend on the type and amount of the mutagen, the organism's DNA repair systems, and where the mutation is in the genome.

 

Suppressor Mutations: Suppressor mutations are those that can turn a mutant organism back into a wild-type one. They can be found in different genes and work in different ways. There are two kinds of suppressor mutations: those that happen inside a gene and those that happen between genes.

 

Intragenic suppressor mutations happen in the same gene as the original mutation. They can make the gene work like it did when it was normal. Mutations like missense mutations, frameshift mutations, and splice-site mutations can lead to intragenic suppressors. For example, a missense mutation that changes just one amino acid in a protein can make it stop working, but a second missense mutation that brings back the original amino acid can bring back the function.

Intergenic suppressor mutations happen in genes that are not affected by the original mutation.

 

They can make up for the loss of function caused by the original mutation. Intergenic suppressors can happen in several ways, such as when mutations happen in regulatory genes, in genes that code for proteins that interact with each other, or in genes that code for alternative metabolic pathways. For instance, if a mutation turns off a gene that codes for an enzyme in a metabolic pathway, it can be made up for by a mutation that turns on a different metabolic pathway.

 

Q5ii) What are transposable genetic elements? How can they cause mutations? (5)

Ans) Transposable genetic elements, also called "jumping genes" or "transposons," are long stretches of DNA that can move around within and between genomes. They are found in all living things, from bacteria to humans, and cause a lot of genetic variation in populations.

 

There are two main types of transposons: Class I, which are called retrotransposons, and Class II, which are called DNA transposons. Retrotransposons move by a "copy and paste" process in which an RNA intermediate is copied from the transposon DNA, reverse-transcribed back into DNA, and inserted at a new location in the genome. DNA transposons, on the other hand, move through a process called "cut and paste," in which the transposon DNA is taken out of one place in the genome and put back in another.

 

Mutations can happen in many ways when transposable elements are present. First, when a transposon moves to a new spot in the genome, it can mess up the coding sequence of a gene. This can cause the gene to stop working or give the organism a "mutant" look. Transposons can sometimes move into the parts of genes that control how the gene is expressed. Second, when transposons move, they can cause changes to the chromosomes, such as inversions, deletions, and duplications. These changes can cause genes to stop working or change how they are expressed. Lastly, transposons can cause mutations by putting themselves in or near genes that are involved in DNA replication, repair, or recombination. This can cause mistakes in these processes and cause more mutations to happen.

 

Induced mutations, which are mutations caused by things like radiation or chemicals, can make transposition happen more often by damaging DNA and making places for transposons to insert themselves. This can make it more likely that transposons will cause mutations.

 

Suppressor mutations are mutations that can help a mutant with a bad gene get back to its normal state, either partially or completely. Transposon insertions can sometimes cause these suppressor mutations. For example, a transposon insertion in a gene that stops a defective gene from being expressed can bring back normal gene function and change the way the mutant looks. On the other hand, putting a transposon in a regulatory part of a gene can make the gene more active and make up for the loss of function caused by a mutant allele.

 


Part-B

 


Q6) Explain Neo Darwinism and Neo Lamarckism in detail. (10)

Ans) Neo-Darwinism and Neo-Lamarckism are two 20th-century theories of evolution that are different from each other. Neo-Darwinism, also called the Modern Synthesis, is a continuation of Charles Darwin's theory of evolution by natural selection, while Neo-Lamarckism is an updated version of Jean-Baptiste Lamarck's theory of evolution by the inheritance of acquired traits.

 

Neo-Darwinism: Neo-Darwinism tries to explain how species came to be by combining Darwin's theory of natural selection with modern genetics. This theory says that evolution happens through a combination of genetic changes and natural selection. Genetic mutations are random changes in an organism's DNA sequence that can cause new alleles to form. These alleles are affected by natural selection, which favours those that give an advantage in a certain environment.

 

Neo-Darwinism puts a lot of focus on how genetic differences play a part in evolution. Genes change because of mutations, which can happen on their own or be caused by things in the environment like radiation or chemicals. As mutations happen over time, they lead to the creation of new species.

 

Neo-Darwinism also talks a lot about how important reproductive isolation is to the development of new species. When a group of organisms becomes reproductively isolated from other groups, this is called reproductive isolation. This can happen when people are separated from other people in their area or when they stop mating with people from other groups.

 

Neo-Lamarckism: Neo-Lamarckism is an updated version of Lamarck's theory of evolution, which was made in the early 1800s. Lamarck thought that organisms could get new traits by using or not using organs, and that these traits could be passed on to the next generation. Lamarck thought, for example, that giraffes' long necks grew over time as they stretched to reach higher leaves on trees.

 

Neo-Lamarckism also stresses the role of the environment in evolution, but it is different from Lamarck's original theory in that it says that acquired traits can be passed down through changes in gene expression. Neo-Lamarckism says that changes in an organism's environment can cause epigenetic changes in its DNA. These changes can then be passed on to the organism's offspring. These changes can cause traits that were learned to be passed on, such as changes in behaviour, physiology, or shape.

 

Critique: Neo-Darwinism is the most popular theory about how species change over time. Focusing on genetic variation and natural selection has made it easier to understand how species change over time. But Neo-Darwinism has its critics, especially when it comes to how it explains how complex traits like eyes or wings came to be. Some people say that the addition of small changes over time is not enough to explain how complex traits develop.

 

On the other hand, modern biology has shown that Neo-Lamarckism is mostly wrong. It has been shown that acquired traits can't be passed down because changes in gene expression don't lead to changes in DNA that can be passed down. But the role that environmental factors play in evolution is becoming clearer, and some cases have shown that epigenetic changes play a role.

 

Q7i) Industrial melanism is an excellent model to demonstrate the natural selection in action. Analyse the above statement critically. (5)

Ans) Industrial melanism is a change in the number of dark-coloured people in a population that is caused by changes in the environment. People often use this idea to show how the process of natural selection works. But it has also been criticised because there are some things it cannot do and some exceptions.

 

Peppered moths in Britain during the Industrial Revolution were the best example of industrial melanism. Before the industrial revolution, Britain's trees were covered in light-coloured lichen, and peppered moths were a mix of white and black, which helped them blend in with their surroundings and avoid being eaten. But because of pollution from factories, the soot made the trees darker, and the dark-coloured melanic form of peppered moths became more common because they could blend in better with the darker environment. This helped them hide from their predators. The process of natural selection is to blame for this change in the number of melanics in the population over time.

 

Industrial melanism is a great example of how natural selection works in the real world. Natural selection is the process by which people with good traits are more likely to live and have children, so that their good traits are passed on to their children. In the case of industrial melanism, the dark-coloured form of the peppered moth was more likely to survive in the polluted environment than the light-coloured form. This caused the dark-coloured form to become more common in the population. This change in how often melanics appear over time shows how natural selection works.

 

But the idea of "industrial melanism" has also been criticised because it has some limits and exceptions. One of the biggest problems is that it only shows one example of natural selection, and there aren't many other examples that show the process so clearly. Industrial melanism is a unique event because it shows how natural selection can work in a population in a way that can be seen. But most examples of natural selection are not so obvious and can't be seen in this way.

 

Another problem is that industrial melanism is not always seen in all species. When the environment changes for some species, the number of people with certain traits doesn't change. In the case of the marsh-dwelling sparrow, for example, the rise in air pollution did not change the number of dark-coloured people in the population. This suggests that the process of natural selection doesn't always work.

 

Q7ii) What do you understand by sexual selection. Illustrate your answer with a suitable example. (5)

Ans) Sexual selection is a type of natural selection that occurs because of differences in mating success between individuals. It is the process by which individuals of one sex, usually males, compete for access to the other sex, usually females, to mate and reproduce. Sexual selection is believed to be responsible for the evolution of many traits, including brightly coloured feathers, elaborate courtship displays, and exaggerated body size or structure.

 

One example of sexual selection can be seen in the peacock, where the male peacock has evolved elaborate, brightly coloured feathers and an elaborate courtship display. These traits have evolved because female peacocks have a strong preference for males with these characteristics, and therefore, males that possess them are more likely to successfully mate and pass on their genes. The bright color of the peacock's feathers, which are caused by iridescence rather than pigmentation, are thought to be a signal of good health and genetic quality, as well as an indication of the male's ability to survive and reproduce despite the handicap of carrying such a cumbersome and conspicuous feature.

 

Another example of sexual selection is seen in elephant seals, where males compete for access to breeding females. The largest, strongest males can establish territories and defend them against other males, thereby gaining access to a larger number of females. In elephant seals, sexual selection has led to the evolution of exaggerated male traits, including large size, powerful jaws, and the ability to produce loud, resonant vocalizations that can be heard from a great distance.

 

Sexual selection is an important factor in the evolution of many traits and behaviours in animals, and it has played a key role in the development of the diversity of life on Earth. By driving the evolution of sexually selected traits, sexual selection can lead to rapid evolutionary change and the development of new species over time.

 

Q8) What is Isolation and what are its types? Explain. (10)

Ans) Isolation is when two or more groups of the same species live in different places and can't breed with each other. Because of this, there is less genetic exchange between the populations, which means that different traits and, eventually, new species will develop.

 

There are many kinds of isolation, such as:

  1. Geographical Isolation: This happens when something like a mountain range or an ocean stands between two populations. Because of this, there is less gene flow between them, and over time, they may become two different species.

  2. Ecological Isolation: This happens when groups of people live in different places, act differently, or like different things. For instance, one group of animals might like a certain kind of food or a certain place to mate, while another group might like something else. Over time, these differences can cause two different species to form.

  3. Temporal Isolation: When two or more populations breed at different times of day, year, or season, this happens. One group might have babies in the spring, while another might have babies in the fall. This can stop the groups from sharing genes, which can lead to the rise of two different species.

  4. Behavioural Isolation: This happens when the ways or rituals that two or more populations use to mate are different. For instance, one group might put on elaborate displays of love while another group might not. Over time, these differences can lead to the rise of new species.

  5. Mechanical Isolation: This happens when the reproductive structures of two or more populations are different enough that they can't mate. For example, the way one group reproduces might not work with that of another group, which would stop them from mating.

  6. Gametic Isolation: This happens when two or more populations can't make healthy babies because their gametes are different (sperm and egg). For example, because their genes are different, the sperm of one group might not be able to fertilise the eggs of another group.

 

The Galapagos finches are a good example of how isolation can lead to different species. These birds live on different islands in the Galapagos archipelago. To adapt to their different environments, their beaks have grown to be different sizes and shapes. Over time, these differences have grown to the point where the birds on different islands are now thought of as different species. The birds were separated by large distances and could not breed with each other, which was a big part of how these species evolved. The birds on each island also had to adapt to different food sources and environments, which led to different beak sizes and shapes.

 

Q9) Answer in about 50 words each. (10)

a) Explain the concept of geographical isolation with suitable examples.

Ans) When a mountain range, river, or ocean divides a community, reproductive isolation occurs. Different selective forces may cause these groups to evolve diverse features and speciate. For instance, the Grand Canyon has separated communities of flora and animals on either side.

 

b) How does habitat preference of organisms promote speciation process?

Ans) Habitat preference causes reproductive separation between populations in different habitats, which promotes speciation. Over time, genetic and phenotypic differences between populations may make interbreeding and offspring production impossible. Two populations of fish in different settings, such as a lake and a river, may develop variations in their physical traits, behaviour, and mating techniques that prevent them from interbreeding, resulting in the establishment of new species.

 

c) Cite an example to show that highly restricted breeding seasons of populations contribute to isolation process.

Ans) The North American wood warbler is an example of a species that became isolated because its breeding season was so short. Different types of warblers have different times of year when they breed. Some breed early in the season, while others breed later. This difference in timing can lead to temporal isolation, which keeps different species from mixing even if they live in the same place. Over time, this can lead to the birth of new species.

 

d) Discuss the role played by courtship behaviour and scents in the isolation process.

Ans) Courtship behaviour and fragrances create prezygotic barriers that isolate populations. If courtship rituals and displays differ between populations, interbreeding may be prevented. Scents or pheromones can attract mates, but differences in scent can inhibit mating between populations. Bird species have unique courtship songs to avoid hybridization by identifying their own partners.

 

e) Distinguish the terms interspecific sterility and hybrid sterility.

Ans) Interspecific sterility prevents people of different species from having offspring. Hybrid sterility prevents cross-species reproduction. Interspecific sterility prevents two species from mating, and hybrid sterility prevents offspring from generating gametes. Hybrid sterility makes mules, the offspring of horses and donkeys, sterile. Because they are different species, lions and tigers can't have healthy offspring.

 

Q10) Analyse the causes and influence of big five mass extinctions. (10)

Ans) Some of the most important events in the history of life on Earth happened during the big five mass extinctions. They were responsible for killing off a lot of life on Earth and have had a huge effect on how life has changed over time. Here, we will talk about what caused each of the big five mass extinctions and how they affected the world.

 

End-Ordovician Extinction: About 443 million years ago, at the end of the Ordovician period, there was the first mass extinction. Climate change and a drop in sea levels are thought to have caused this extinction. As the Earth cooled, glaciers formed, and sea levels fell. This made shallow water habitats disappear, which many organisms needed. Up to 85% of marine species died out because of this extinction event, which makes it one of the worst in Earth's history.

 

Late Devonian Extinction: About 359 million years ago, during the Late Devonian period, there was a second mass extinction. Climate change and a drop in the amount of oxygen in the air are likely to blame for this extinction. As the Earth got cooler, the sea levels dropped and the weather changed, which led to a drop in the number of marine species. Up to 70% of marine species died out because of this extinction event, which also had a big effect on how early vertebrates evolved.

 

End-Permian Extinction: About 252 million years ago, at the end of the Permian period, there was a third mass extinction. This was the worst extinction event in Earth's history. Up to 96 percent of marine species and 70 percent of land species died out because of it. The cause of this extinction is thought to be a combination of climate change, volcanic activity, and a drop in oxygen levels. Large-scale volcanic eruptions in what is now Siberia caused a big rise in carbon dioxide levels in the air and a rise in temperatures around the world. This, in turn, caused the oceans to become more acidic and oxygen levels to drop, which was terrible for marine life.

 

End-Triassic Extinction: About 201 million years ago, at the end of the Triassic period, there was a fourth mass extinction. This extinction is thought to have been caused by a mix of volcanic activity and changes in the climate. Large-scale volcanic eruptions in what is now the Atlantic Ocean caused a big rise in the amount of carbon dioxide in the air, which caused temperatures to rise around the world. This, in turn, led to a drop in the number of species, especially marine ones.

 

End-Cretaceous Extinction: The fifth and most well-known mass extinction happened at the end of the Cretaceous period, about 66 million years ago. This event is often called the "dinosaur extinction" because it killed off all dinosaurs that were not birds. It is thought that a large asteroid impact and volcanic activity caused this extinction. When the asteroid hit, it made a huge cloud of dust that blocked out the sun and caused global temperatures to drop by a lot. This had a terrible effect on the food chain, causing many species to go extinct.

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