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MANE-001: Human Genetics

MANE-001: Human Genetics

IGNOU Solved Assignment Solution for 2021-22

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Assignment Code: MANE-001/AST/TMA/2021-22

Course Code: MANE-001

Assignment Name: Human Genetics

Year: 2021-2022

Verification Status: Verified by Professor


Note: Attempt any five questions. Choose at least two questions from each section. All questions carry equal marks. The word limit for 20 marks is 500 words and for 10 marks is 250 words.



Section A



Q1) What is Human Genetics? Briefly elucidate different branches of Human Genetics. 20

Ans) Human genetics can be defined as a branch of science concerned with the transmission of traits down the generations. However, the mechanisms governing inheritance patterns are not always simple, as in the case of complex traits, they may involve interactions of genes with non-genetic and environmental factors.


Branches of Human Genetics

Cytogenetics

The study of chromosomes, or hereditary units, is known as cytogenetics. It has been an active field of research that has contributed to our understanding of chromosome organisation and the human genome. It's a science that matches phenotypes to chromosomal abnormalities that can be seen. To put it another way, abnormal changes in the number or structure of chromosomes in an individual can be linked to clinical signs and symptoms.


Biochemical Genetics

Biochemical genetics, by definition, is concerned with the transmission of genes that control the activity of an enzyme that catalyses a specific biochemical reaction in a metabolic pathway. When a gene malfunctions, it causes a block in the biochemical pathways catalysed by the enzyme in question. This causes the product to accumulate prior to the block, preventing other reactions in the pathway from continuing.


Immunogenetics

Immunogenetics can be defined as the study of the immune response's molecular and genetic basis. Immunogenetics has made significant contributions to our understanding of certain disorders in recent years. Antigens and antibodies distinguish self from nonself antigens in the immune system. Immune reactions are highly specific, and antigens only react when they come into contact with specific antibodies, which works like a lock and key. ABO blood groups are important in blood transfusions because blood can only be given from one person to another if the donor and recipient have antigenic compatibility.


Pharmacogenetics

Pharmacogenetics is a rapidly expanding field that deals with the inheritance of drug sensitivity in humans. The sensitivity to the chemical phenylthiocarbamide or the related compound phenylthiol-urea, which is inherited as an autosomal dominant trait in humans, is a classic example. Tasters are people who can detect such compounds at microscopic levels, while non-tasters are people who can't. As a result, the ability to taste PTC is thought to be more important than the inability to taste it. Non-tasters are found to have a higher risk of developing gout, a type of arthritis.


Molecular Genetics

Molecular genetics is defined as the study of any genetic condition caused by changes in the nucleotide sequence of DNA that represents a gene. The development of recombinant DNA technology, in which a normal or desired gene sequence is introduced into the genome of a vector and the recombinant molecule with the vector and introduced gene sequence is multiplied inside a host, usually a bacterium or artificial chromosomes of yeast, bacteria, or mammalian cells, accelerated the study of genetic diseases at the molecular or DNA level in the mid-1970s.


Somatic Cell Genetics

Somatic cell genetics is a branch of genetics concerned with the fusion of somatic cells from various species in order to conduct genetic studies on the hybrid cells. Somatic cell genetics was a major breakthrough in the 1960s because it eliminated the need to wait for the next generation to trace the inheritance of traits from parents to offspring.


Population Genetics

A population is a collection of interbreeding individuals and their descendants. Population genetics is the study of the frequencies of different alleles in different populations and the mechanisms that cause genetic diversity.


Genomics

The structural and functional studies of the genome, which represents the total content of DNA within an organism or cell, including nuclear and mitochondrial DNA, can be defined as genomics. The human genome is made up of 3.2 billion nucleotides and 20,000 genes, plus the gaps in between. The sequence is being annotated in order to create a complete map of the human genome. The human genome's organisation, which includes coding and non-coding sequences, unique and repeated sequences, and so on.


Clinical Genetics

Clinical genetics is the branch of genetics concerned with determining the genetic involvement in a disease or disorder, as well as its treatment and management. In the practise of clinical genetics, three cardinal principles should be strictly observed: genetic heterogeneity, pleiotropism, and variability. Genetic heterogeneity is defined as the occurrence of one and the same or nearly identical phenotypes with different modes of inheritance. This has a variety of implications in genetic counselling.


Q2) What is Meiosis cell division? Discuss briefly the different stages of cell division with suitable diagrams. (20)

Ans) Farmer discovered meiosis cell division in 1905. Because the diploid (2n) chromosomes are reduced to haploid, it is also known as reduction division or reproductive division (n). Only reproductive (germ) cells are affected. Meiocytes are the cells in which meiosis takes place. It is more difficult to understand than mitosis.


Meiosis has two stages as follows:

  1. The diploid cell is divided into two haploid cells during heterotypic division (First Meiotic Division).

  2. The two haploid cells from the first division divide into four haploid cells during homotypic division (second meiotic division). In terms of chromosome number, the daughter cells are similar to the parent cells.


It's worth noting that the centromere does not divide during the first meiotic division, resulting in a reduction in the number of chromosomes. The centromeres, not the chromatids, divide during the second meiotic division.


The first stage of meiosis (prophase) consists of five distinct stages:

First Prophase

  1. The diploid chromosome appears in the nucleus of the leptotene.

  2. Zygotene: Identical chromosomes come close together and pair along their entire length. This is referred to as a synopsis. The paired chromosomes are now in a Bivalent state.

  3. Pachytene: The bivalent chromosomes coil around each other and shorten, resulting in haploid chromosomes.

  4. Diplotene: A chromosome splits longitudinally into two chromatids.

  5. Diakinesis occurs when chromosomes coil and become even shorter. They are still dispersed throughout the nucleus.


Further stage of Meiotic division is known as Meiosis II. In addition to First Prophase, Meiosis consists of the following stages.

Second Prophase

  1. The nuclear membrane vanishes, the nucleolus vanishes, the nuclear spindle develops, and bivalent chromosomes move towards the equatorial plane in the first metaphase. There are two centromeres on each chromosome, which are attached to spindle fibres.

  2. The two pairs are now separated and move to opposite poles in the first anaphase.

  3. First Telophase: Two daughter nuclei form at the poles, each with a pair of chromatids. There are haploid nuclei in the nuclei.

  4. The paired chromatids are widely separated in the second metaphase, and the point of attachment is at the centromere.

  5. The chromatids separate in opposite poles during the second anaphase.

  6. Second Telophase: Four daughter nuclei with haploid (N) chromosomes each are formed.


Genetic Significance of Meiosis

  1. Meiosis produces gametes, which are necessary for sexual reproduction.

  2. Meiosis converts the diploid (2n) chromosomes found in somatic cells to the haploid number (n) found in gametes.

  3. Meiosis prevents chromosome duplication in the zygote, which would otherwise be abnormal.

  4. In a given species, meiosis keeps the number of chromosomes constant.

  5. Because of the crossing over, meiosis provides a new combination of genetic material. Hereditary factors (genes) from males and females mix, resulting in genetic differences between species. Evolution is primarily driven by variations.

  6. The term "meiotic drive" refers to a disruption in the 1:1 sex ratio.


Q3) What is Hardy Weinberg Equilibrium? Briefly examine the factors affecting change in gene frequency. 20

Ans) Hardy-Weinberg The answer to an intriguing question is equilibrium: what happens to the gene frequency of a dominant character in a population over generations. The following are the factors that influence gene frequency changes:


Mutation

A mutation is a once-in-a-while change in phenotypic or genotypic forms in a population. In a population, the probability or likelihood of occurrence is on the order of one in several lakhs or tens of thousands of people. For example, mutation is the cause of several Mendelian syndromes and disorders that have been discovered in human populations. In most cases, it is a single mutation or a point mutation. At the molecular level, mutations are changes in DNA sequences in an individual's genome that cause non-normal phenotypic manifestations, some of which are clinically or medically identified as diseases or syndromes.


Genetic Drift

The non-systematic evolutionary force of genetic drift is significant. Let us first define the term "drift" in order to comprehend the concept of genetic drift. For example, drifting in the air, wind, and water, or in the ocean. In a small population, similar phenomena can occur when it comes to gene frequency. In small populations, population size is drastically reduced as a result of population-events such as pandemic diseases, earthquakes, and so on, which can have a significant impact on genetic diversity and gene frequency: for example, gene frequency can drift from one generation to the next at random, resulting in either loss or fixation of alleles over generations.


Natural Selection

Natural selection is one of the most important factors (key mechanisms) in evolution, according to Charles Darwin. Natural selection occurs when different genotypes have different rates of reproductive success. For example, how selection works at the molecular (genome) level, particularly changes in gene frequency, which are theoretically considered in population genetics. Because these variants of the trait have different reproductive success, there will be more offspring with the variant than those with other variants of the trait. Fitness, in the Darwinian sense, refers to the ability to successfully contribute to the next generation. It's also known as 'adaptive value' or ‘selective value.' As a result, if fitness differences are linked to the presence or absence of a specific allele in an individual's genotype, selection operates at the genetic level.


Gene Flow

  1. Migration, also known as gene flow, is a significant factor that can alter gene frequency. Individuals' gene frequencies can be altered or changed as a result of emigration or immigration between populations.

  2. Gene flow between two subpopulations can occur as a result of random mating, admixture, or marriages. Anglo Indians and American Blacks are examples of genetically admixed populations.

  3. Gene flow stumbling blocks: Local subpopulations form as a result of endogamy, which is facilitated by geographical, cultural, linguistic, political, and other factors.

  4. Theoretical Gene Flow Models: These are important factors to consider when estimating or modelling gene flow between populations. In terms of population genetics, the genetic diversity of populations decreases as their distance or geographical location increases.


Genetic Equilibrium

Mutation, selection, and drift may all work against each other to create a dynamic equilibrium in which allele frequencies don't change. The Hardy-Weinberg genotype frequencies persist indefinitely in a randomly mating population without selection or drift to change allele frequencies, and without migration or mutation to introduce new alleles. A genetic equilibrium exists in such an idealised population. In reality, the situation is far more complex; selection and drift, migration, and mutation are all working to alter the genetic composition of the population. However, these evolutionary forces may act in opposition to one another, resulting in a dynamic equilibrium with no net change in allele frequencies.


Q4) Discuss different types of chromosomal aberrations in man. 20

Ans) The four kinds of aberrations of chromosomes are of great importance in human genetics:


Deletions (Deficiencies)

A chromosome lacks either an interstitial or terminal chromosomal segment, which may include only a single gene or part of a gene, in a deletion or deficiency type aberration. When a chromosome breaks near the end, a small piece of the terminal end is lost, resulting in terminal deficiency. Two breaks can occur at any two points on an intercalary segment, releasing a rod-shaped or ring-shaped intercalary segment. If the broken ends of the intercalary segment join and fuse, a ring-shaped chromosome called deletion ring is formed. The original chromosome's broken ends are fused, resulting in intercalary or interstitial deficiency. A deletion occurs when a portion of a chromosome is lost, resulting in partial monosomy. Breakage can be caused by a variety of factors, including irradiation, chemicals, drugs, and viral infections.Deletions occur in one of two ways:

  1. During the cell cycle's interphase, a chromosome breaks, and the broken piece is lost when the cell divides.

  2. During mitosis, parts of chromosomes are lost due to unequal crossing-over.


Duplications

Chromosomes with an extra part and gene sequences are known as duplications. Only large duplications could previously be seen in karyotypes, and the more genes involved, the more severe the resulting syndrome. Small duplications are usually less severe than small deletions. Repeats, which are small duplications involving only a few genes, can be tolerated. Indeed, such duplications are thought to be a key evolutionary mechanism for the emergence of "new genes." Unequal crossing-over is the most common cause of large unwanted copies of portions of the chromosome. Because large portions of one chromosome are usually present in triplicate, most disorders caused by duplications are classified as partial trisomies.


Inversions

An inversion involves breaks:

  1. Repair occurs in the form of reversal of the broken segment on one chromosome.

  2. as well as the restitution of the broken ends.

  3. As a result, the chromosome is inverted.


The genes on this chromosome are normally ordered ABCD, but they are ordered ACBD on the inverted chromosome. There are two types of inversions, depending on whether or not the centromere is included in the inverted section:

  1. When the centromere is outside the inverted segment, it is called paracentric inversion.

  2. When the centromere is included in the inverted segment of the chromosome, it is called pericentric inversion.


Translocations

Translocation is a type of structural abnormality that occurs when a segment of one chromosome is detached and reattached to another, usually nonhomologous, chromosome in a man. This structural rearrangement has genetic significance because genes from one chromosome are transferred to another. These are of two types:

  1. Reciprocal translocation.

  2. Nonreciprocal translocation.


The structural rearrangement when segments of two nonhomologous chromosomes are interchanged without any net loss of genetic material is referred to as reciprocal translocation. A Robertsonian translocation is a type of nonreciprocal translocation in which two nonhomologous acrocentric chromosomes' centromeric regions fuse to form a single centromere.


Q5) Write short notes on any two of the following:

a). Fluorescence in Situ Hybridization (10)

Ans) It entails the pairing of a genetic "probe" sequence with its complementary region in the human genome. The target chromosomes must first be denatured in order to accomplish this. Of course, the probe is made up of DNA, RNA, or cDNA from the gene of interest. The probe is a strand of labelled oligonucleotide that is used to pinpoint a gene's location on a chromosome. The principle behind this method is to select probes with higher specificity.


Early research used radioactive isotopes to label probes and autoradiography to identify target sequences. The sensitivity and resolution of the technique are both limited by this method of labelling and detection. The original protocol, in particular, could only detect tandemly repeated sequences like ribosomal genes and satellite DNA. However, the technique isn't perfect because single-copy radioactive probes can't determine gene localization within a single cell's chromosomes; instead, a statistical analysis of silver grain distributions in 50-100 sets of metaphase chromosomes is required.


FISH (fluorescence in situ hybridization) is a cytogenetic technique used to detect and localise the presence or absence of specific DNA sequences on chromosomes that was developed by biomedical researchers in the early 1980s. FISH uses fluorescent probes that only bind to parts of the chromosome that have a high degree of sequence complementarity. FISH is frequently used in genetic counselling, medicine, and species identification to find specific features in DNA. FISH can also be used to locate and detect specific mRNAs in tissue samples. It can also aid in defining the spatial temporal patterns of gene expression within cells and tissues in this context.


b). ABO blood group system (10)

Ans) Serum and cells are the two main components of blood. The sera of some people caused the red cells of others to agglutinate, according to Karl Landsteiner. The ABO blood group systems were developed as a result of this observation. He was able to categorise people into three groups based on the reactions between red blood cells and serum: A, B, and O. Two of his students discovered the fourth and most rare type, AB, two years later. A, B, and O groups were described by Landsteiner, and the fourth type, AB, was discovered in 1902 by Alfred von de Castello and Adriano sturli.


Karl Landsteiner was born in Vienna, Austria, on June 14, 1868. In 1897, he pursued his interest in immunology, and in 1901, he published his findings on the human ABO blood group system. He was awarded the Nobel Prize in Physiology or Medicine in 1930 for discovering the major blood groups and developing the ABO blood typing system, which enabled blood transfusions. Because of the less developed communication system at the time, it was later discovered that Czech serologist Jan Jansky had also independently pioneered the classification of human blood into four groups, though his name is not well known outside of Russia and the former Soviet republics. Around the same time in America, Moss published a similar work on blood groups in 1910.


The heritability of ABO blood groups was discovered by Ludwick Herzfeld and von Dungern in 1910–11. In 1924, Felix Bernstein is credited with discovering that the blood group inheritance pattern is due to multiple alleles at one locus.



Section B



Q6) Define DNA polymorphism. Examine any two techniques used in molecular genetics. 20

Ans) Different DNA sequences among individuals, groups, or populations are known as DNA polymorphisms. Polymorphism in DNA can take many forms, including single base pair changes, multiple base pair changes, and repeated sequences. There are an infinite number of DNA polymorphisms, and new ones are being discovered all the time.


Two techniques used in molecular genetics are as follows:

Polymerase Chain Reaction

Kary Mullis developed the revolutionary PCR (Polymerase Chain Reaction) method in the 1980s. In genetics and molecular biology, it is a necessary and ubiquitous tool. This technique can be used to clone DNA in vitro. The ability of DNA polymerase to synthesise new strands of DNA complementary to the template strand is used in PCR. Because DNA polymerase can only add a nucleotide to a 3'-OH group that already exists, it requires a primer to add the first nucleotide. This criterion allows the researcher to define a specific region of the template sequence that he or she wants to amplify. The specific sequence will be accumulated in billions of copies at the end of the PCR reaction (amplicons). Because dye termination sequencing requires multiple copies of DNA, PCR is used to generate a large number of copies of the DNA fragments of interest, which are then sequenced. The genomic DNA of each subject can be amplified on thermal cycler with an initial denaturation at 960C for 3 minutes and later on for 35 cycles at 950C for 60 seconds, at estimated annealing temperature of the primer for 45 seconds, extension at 720 C for 2.30 minutes and a final extension at the end of 35th cycle at 720C for 7 minutes in a final volume of 10 μl containing 50mM KCl, 10mm Tris, 1.5mM MgCl2, 75 ng of each primer, 100 μM deoxy-NTP, and 1 U Taq polymerase.


Restriction Fragment Length Polymorphism

American geneticist David Botstein, biochemist Ronald W. Davis, population geneticist Mark Skolnick, and biologist Ray White proposed the restriction-fragment length polymorphism (RFLP). Restriction fragment length polymorphisms (RFLPs) can be used to map the genes that cause disease in humans and to create a linkage map of the human genome. The analysis of Restriction Fragment Length Polymorphism (RFLP) fragments of DNA containing short sequences that differ from person to person, known as VNTRs, is done. We can use restriction enzymes to cut DNA at specific points after extracting DNA from a sample and amplifying it using the Polymerase Chain Reaction technique. To determine how many times a given VNTR is repeated, the fragments can be sorted by length using gel electrophoresis technology. The samples could not have come from the same person if they show VNTRs of different lengths in two different samples. Two samples with the same length VNTRs, on the other hand, could have come from the same person or from two people who happened to have the same length VNTRs at that location. The likelihood of a coincidental match can be reduced to nearly zero by comparing enough VNTRs from two individuals. RFLP testing takes hundreds of steps and weeks to complete, and newer, faster techniques have largely replaced it.


Q7) What is Human Genome Project? Briefly discuss the applications of Human Genome Project. (20)

Ans) The human genome project was an international effort to sequence and identify every nucleotide in the human genome. The US Department of Energy and the National Institutes of Health were in charge of coordinating this effort (NIH). It was the most well-funded biology programme ever, with collaborators from the United Kingdom, Japan, and Germany.


Applications of Human Genome Project

Molecular Medicine

The knowledge gained from HGP has ushered in a new era of molecular medicine and biotechnology. Instead of treating a disorder based on its symptoms, molecular medicine looks for the underlying causes of diseases. Its goal is to develop faster and more accurate diagnostic tests or genetic screening for the early detection of a wide range of diseases, allowing for effective treatment, particularly for single gene disorders. In addition, it investigates genetic factors that contribute to susceptibility to common complex conditions, as well as environmental factors and people's smoking habits and addictions.


Risk Assessment

Human genome analysis has revealed that nucleotide differences exist between individuals, which could be linked to their susceptibility or resistance to disease-causing factors. This information will also be useful in determining the health effects and risks associated with long-term low-dose exposures to radiation, as well as exposure to chemicals and toxins that cause harmful mutations, cancers, and infections. This knowledge will aid in the modulation of necessary preventive measures to maintain a healthy society and general health status.


Energy and Environment

DOE established the Microbial Genome Program in 1994 to sequence the genomes of bacteria in order to gain knowledge that will benefit human health and the environment, as well as improve the economy through industrial applications. The development of new energy-related biotechnologies will be aided by the characterization of complete microbial genomes:

  1. like photosynthetic systems

  2. production of biofuels

  3. microbial systems that work in extreme environments

  4. organisms that can metabolise readily available renewable resources and waste material.


It is possible to create a wide range of new products, processes, and testing methods that will aid in the preservation of a pollution-free environment.


Anthropology, Evolution and Human Migration

Genomic information facilitated:

  1. Through germ line mutations in lineages, we can gain a better understanding of human evolution.

  2. Humans and all other forms of life share a common biology.

  3. Investigate the migration patterns of various populations based on female genetic inheritance.

  4. The Y chromosome can be used to track male lineage and migration.

  5. Identify mutations and correlate breakpoints in mutation evolution with population ages and historical events.


Forensic Science

Genome sequences differ by species and are unique to each individual. As a result, genome sequence information is used in forensic science for the following purposes:

  1. identifying criminals who committed crimes as victims

  2. Exonerate those who have been wrongfully accused.

  3. Identify the perpetrators of crime and the victims of catastrophic events.

  4. In cases of disputed parentage, establish paternity and locate relatives.

  5. For organ transplantation, organ donors and recipients are matched.


Furthermore, by analysing endangered and protected species' genomes, it is possible to identify endangered and protected species in the wild. Bacteria and other organisms that may pollute the air, water, soil, and food can be detected. In breeding experiments, genomic information also aids in determining plant and livestock pedigrees.


Agriculture and Livestock Breeding Drought

Plant and human genome research allows for the development of disease-resistant plants as well as more nutritious and pesticide-free foods. Insect, pest, and drought-resistant bioengineered seeds are already on the market. Similarly, genome information is being used to develop disease-resistant live stocks as well as those that are more productive in terms of meat and milk yield.

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