Genetic Variation PDF

Genetic varıatıon Ezgi G. Berkay, MD, PhD Definitıons SPECIES  groups of organisms that are sufficiently similar to reproduce to produce fertile offspring Population  a group of the same species living in an area where no two individuals are exactly alike due to variations that individuals can sur...

Genetic varıatıon Ezgi G. Berkay, MD, PhD Definitıons SPECIES  groups of organisms that are sufficiently similar to reproduce to produce fertile offspring Population  a group of the same species living in an area where no two individuals are exactly alike due to variations that individuals can survive and transmit these traits ALLELE  An allele is an alternative form of a gene. Organisms typically have two alleles for a single trait, each inherited from a different parent. ALLELE FREQUENCY  a measure of how common an allele is in a population GENE POOL  all alleles of all species in a population What is the mutation? Modification, deletion, or addition of a base pair. Chromosomal deletion, insertion, or rearrangement. Somatic mutations occur in  somatic cells and affect only the individual in which the mutation occurred. Germ-line mutations  replace gametes and pass them on to the next generation. Mutation rate = probability of a particular type of mutation per unit time (or generation). Mutation frequency = the number of times a particular mutation occurs in a population of cells or individuals. Genetic diversity in a population can increase some individuals' chances of survival. Phenotype  A trait produced by one or more genes that provides diversity in the gene pool. Examples: body size, feather patterns Genetic variation leads to phenotype variation. Phenotype variation is required for natural selection. Genetic variation is stored in the gene pool of a population. The gene pool consists of all alleles in a population. New combinations of alleles are formed when organisms have offspring. Genetic variation occurs for different reasons: MUTATION Can generate new allele In reproductive cells, it can be passed to offspring. RECOMBINATION Can create new combinations of alleles Usually occurs during meiosis Newly arranged parental alleles in gametes mutaTıons  Definition: Changes in the nucleotide sequence of DNA It may occur in somatic cells (not transmitted to offspring) Can occur in gametes (eggs and sperm) and pass to offspring Mutations happen regularly Almost all mutations are neutral. Chemicals and UV radiation cause mutations Many mutations are repaired by enzymes. Somatic mutations cause some types of skin cancers and leukemia. Some mutations may contribute to the survival of an organism (beneficial) Chromosomal mutatıons - Changes in chromosome structure Chromosome parts may be missing/missing or increasing. Types: - Deletion - Inversion - Translocation - Duplication - Nondisjunction deletıon Caused by breakages A part of the chromosome is lost inversion Chromosome segment breaks The segment rotates around itself. The segment is reconnected. duplicatıon Repeats in DNA sequences translocatıon It contains two non-homologous chromosomes. A part of one chromosome is attached to another. Nondısjunctıon Failure of chromosome separation during meiosis It causes the gamete to have more or fewer chromosomes than the normal set. Disorders: Down Syndrome – three 21st chromosomes Turner Syndrome – single X chromosome Klinefelter Syndrome – XXY chromosome set aneuploidy Excess or deficiency of a particular chromosome Trisomy and Monosomy Trisomy  Presence of an extra copy of a chromosome Monosomy  one chromosome is missing. n = 23 (haploid set; 22 autosomal+1 sex chromosomes)  the number of chromosomes we will see in gametes 2n = 46 (44 autosomal (22x2) + 2 sex chromosomes)  diploid chromosome set If we evaluate it this way; Trisomies  2n+1 Monosomies  2n-1 Gene Mutatıons Change in the nucleotide sequence of a gene. It may contain only one nucleotide or more. It may be due to copying errors, chemicals, viruses, etc. Types: - Point Mutations - Substitutions - Insertions - Deletions - Frameshift Point Mutatıons Change of a single nucleotide Involves deletion, addition, or substitution of ONE nucleotide in a gene frameshift Addition or deletion of one or more nucleotides Changes the "reading frame," like changing a sentence Malformed proteins Insertion Addition of one or more nucleotide base pairs to a DNA sequence Deletion mutation During DNA replication, part of the chromosome or DNA sequence is lost. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. Mutations according to their effects Missense mutation: Base pair substitution results in substituting different amino acids. Nonsense mutation: Base pair substitution results in a stop codon (and shorter polypeptide). Neutral mutation: Base pair substitution results in amino acids with similar chemical properties (protein function does not change). Silent mutation: Base pair substitution results in the same amino acid. Frameshift mutations: Deletions or insertions (not divisible by 3) cause incorrect translation of amino acids, stop codons (shorter polypeptides), or read stop codons (longer polypeptides). Non-mendelian ınheritance Genomic Imprinting Uni-Parental Disomy Mitochondrial Inheritance Dynamic Mutation Genomic imprintıng Depending on the gender of the parent Monoallelic expression resulting from epigenetic marking is called "Genomic Imprinting." The gene is expressed on the paternal or maternal allele in some or all tissues; and shows monoallelic expression. The exact order continues in each generation. The nucleotide sequences of the suppressed and the unimpressed allele are identical. Few human genes show imprinting properties. Thanks! CREDITS: This presentation template was created by Slidesgo, including icons by Flaticon and infographics & images by Freepik