Genetic Variation Contents Introduction Genes and chromosomes Mendels

Genetic Variation

Contents Introduction Genes and chromosomes Mendel’s Law Sources of genetic variation Mutation Gene flow Sexual reproduction Mutation Sexual reproduction Importance Genetic variation and animal behaviour Genetic variation and adaptation Genetic variation and environmental variation Conclusion Reference

Introduction Genetic variation is a term used to describe the variation in the DNA sequence in each of our genomes. Genetic variation is what makes us all unique, whether in terms of hair colour, skin colour or even the shape of our faces. Individuals of a species have similar characteristics but they are rarely identical, the difference between them is called variation. Genetic variation is important in evolution. Evolution relies on genetic variation that is passed down from one generation to the next. Favourable characteristics are selected for, survive and are passed on. This is known as natural selection. Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population.

Genes and chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for specific proteins that functions in one or more types of cells in the body. Genetic variation is a measure of the genetic differences that exist within a population. The genetic variation of an entire species is often called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele. For example, a population with many different alleles at a single chromosome locus has a high amount of genetic variation.

Genetic variation is caused by: Mutation Random mating between organisms Random fertilization Crossing over (or recombination) between chromatids of homologous chromosomes during meiosis The last three of these factors reshuffle alleles within a population, giving offspring combinations which differ from their parents and from others.

Genetic variation in the shells of Donax variabilis: An enormous amount of phenotypic variation exists in the shells of Donax varabilis, otherwise known as the coquina mollusc. This phenotypic variation is due at least partly to genetic variation within the coquina population

Mendel’s Law of Segregation Mendel’s Law of Segregation states that a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent. Mendel’s Law of Independent Assortment Independent assortment allows the calculation of genotypic and phenotypic ratios based on the probability of individual gene combinations.

Sources of genetic variation There are three primary sources of genetic variation, which we will learn more about MUTATIONS GENE FLOW SEXUAL REPRODUCTION Mutations: are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations. Gene flow: is any movement of genes from one population to another and is an important source of genetic variation. Examples Pollen being blown to new destination. People moving to new cities or countries.

Sexual reproduction : introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation. Genetic Drift: Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.

Mutation With these dogs, it is their alleles that make them different. Mutations produce new and different alleles, which is the genetic variation that results in these different phenotypes mutations change the sequence of nucleotides in DNA. Mutations can alter single nucleotides or entire chromosomes (Figure below), and they are the sole source of new alleles.

Classes of mutation Spontaneous Mutation Induced Mutation Spontaneous mutation They are mainly caused during DNA replication or by incorporation of incorrect nucleotide in the growing DNA chain. They occur naturally by changes in DNA sequence during replication.

Induced mutation : Induced mutation are caused by the changes in DNA brought about by some environmental factor called MUTAGENS. Eg. UV light , x-rays, gamma rays etc. . ,

Types of mutation Chromosome mutations Deletion Inversion Duplication Translocation Non disjunction Gene mutation CHROMOSOME MUTATIONS A mutation involving a long segment of DNA. These mutations can involve deletions, insertions , or inversions of sections of DNA. In some cases , deleted sections may attach to other chromosomes , disrupting both the chromosomes that loses the DNA and the one that gains it. Also referred to as a chromosomal rearrangement.

DELETION Deletion is a mutation in which a part of a chromosome or a sequence of DNA is lost during DNA replication. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. INVERSION An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversion are of two types : paracentric and pericentric. DUPLICATION A type of mutation in which a portion of a genetic material or chromosome is duplicated or replicated , resulting in multiple copies of that region. Duplication results from an unequal crossing –over between misaligned homologous chromosomes during meiosis. TRANSLOCATION Translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: Reciprocal an Robertsonian translocation. A gene fusion may be created when the translocation joins two otherwise-separated genes. NONDISJUNCTION There are three forms of nondisjunction : failure of a pair of homologous chromosome to separate in meiosis 1, failure of sister chromatids to separate during meiosis 2, and failure of sister chromatids to separate during mitosis. Non disjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).

GENE MUTATION A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations range in size; they can affect anywhere from a single DNA building block (base pair)to a large segment of a chromosome that includes multiple genes.

Sexual reproduction provides genetic variation because the sperm and egg that are produced contain different combinations of genes than the parent organisms. Sexual reproduction involves meiosis , which is the process of a cell doubling its DNA, shuffling its genes, and then dividing the shuffled DNA among four cells. Genetic material is exchanged. When these sex cells are formed , chromosomes are assorted by chance. In addition , are random egg and sperm combine during fertilization. Sexual reproduction may leads to Random fusion Crossing over Free assortment

Importance of genetic variation Genetic variation is important because it allow individuals with in a given species to adapt to their environment. Remember we are born with adaptation if do not naturally have these difference in our DNA we can not obtain them. If we are different because of genetic variation and we are able to adapt this is known as survival of the natural selection. Adaptation make organisms different and if it occurs over a long enough period of time we can get new species. Genetic variation is diversity within or between species because of their DNA differences. It is necessary to have variation so that natural selection can occur. Difference give individuals different ability to survive and reproduce. This allows for evolution.

Variation and animal behaviour For example in a beetle population , some beetles are green and some are brown. Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential. In this, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. The surviving brown beetles have brown baby beetles because this trait has a genetic basis. The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown. Thus the variation in the gene makes the individuals of the same species to survive and favours natural selection.

Genetic variation and animal adaptation Adaptation is when an organism becomes better matched with its current environment. Adaptations can be structural or behavioural. Structural adaptation : An organism undergoes physical changes to survive. Structural adaptations usually takes place over time due to genetic mutation. That’s the beginning of the relationship between adaptation and genetic variation. Behavioural adaptation: An organism learns a specific behaviour that increases its chance for survival. Behavioural adaptation that occur in an animal’s behaviour or repertoire of actions.

When a habitat changes and a population has to change to survive, variation in the population’s gene pool provides variable traits among the organisms. The variable traits can become dominant through natural selection and ultimately lead to an adaptive change in the population. This allows the species to survive in the new environment. Natural selection allows the fittest individuals to survive, making the population grow stronger.

Genetic variation and environmental variation The ability of an organism to alter greatly its phenotype depending upon environmental conditions. The phenomenon is seen mostly clearly in plants because the diversity of genetic systems is much greater in plants than in animals. The environmental variation is caused by the external environmental factors such as light , temperature, moisture, climate, exposure , etc. . Do not cause changes in the genome , and have no effect on evolution.

Conclusion Genetic variation is important to the processes of natural selection and biological evolution. Natural selection is the result of the interactions between genetic variation and the environment. It states that genetic variation in a species in a population tends to survive in the environment. Evolution has acted so that genes and environment act to complement each other in yielding behavioural solutions to the survival challenges faced by animals. QUESTIONS What is genetic variation Define mutation and explain its types Define gene mutation Explain the sources of genetic variation

Reference https: //en. m. wikibooks. org www. slideshare. net www. sciencedirect. com https: //en. m. wikipedia. org www. nature. com www. pediaa. com https: //courses. lumenlearning. com Human genetics (an overview) -Alice Marcus. Fundamental of genetics -Dr. R. P. Meyyan

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