population genetics presentation p..pptx

Population genetics presentation

1. Departmet of Microbial Cellular & Molecular Biology Title: Genetic diversity and differentiation By: Yosef G. GSR/0338/15

2. Outlines Introduction: definitions of: Genetic diversity differentiation Causes of genetic diversity and differentiation Difference between genetic diversity and genetic variability High and low genetic diversity Steps to assess genetic diversity Markers used to asses genetic diversity and differentiation Metrics of genetic diversity and differentiation: Assessing genetic diversity Measuring genetic diversity Effect of genetic diversity and differentiation 2

3. Introduction Genetic diversity: as a measure of individual variation within a population is widely agreed to reflect the number of different types in the population , taking into account their frequencies. Differentiation: measures variation between two or more populations, demes or subpopulations. As such, it is based on the relative frequencies of types within these subpopulations and, ideally, measures the average distance of subpopulations from their respective lumped remainders. 3

4. causes of genetic diversity and differentiation There are various factors that can cause genetic diversity and differentiation within populations. Some of these factors include mutations , genetic drift , gene flow , natural selection , and environmental factors . Mutations: are changes in the DNA sequence that can introduce new genetic variation into a population. Genetic drift : refers to the random fluctuation of allele frequencies in small populations, which can lead to differences in gene pools between populations. Gene flow: occurs when individuals migrate between populations, which can introduce new alleles and reduce genetic differentiation. Natural selection: favours certain traits and can lead to the fixation of advantageous alleles in certain populations. Finally, Environmental factors: such as geographic barriers or changes in climate can also cause genetic differentiation by limiting gene flow and promoting divergence between populations. 4

5. Difference between genetic diversity and genetic variability Genetic diversity and genetic variability are related terms but they refer to different aspects of genetic variation. Genetic variability: refers to the differences or changes in genetic materials , especially genetic sequences , among individuals of the same species . This variation can occur due to mutations , recombination , or other genetic mechanisms , and it allows for adaptation and evolution of species. Genetic diversity: is the total amount of genetic variation within a population or species, including both the differences among individuals (genetic variability) and t he differences among populations (geographic or ecological). In other words, genetic diversity encompasses the entire range of genetic variation that exists in a species , while genetic variability refers to the specific types of genetic variation that occur within and between individuals . 5

6. Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. Genetic diversity serves as a way for populations to adapt to changing environments . With more variation, it is more likely that some individuals in a population will possess variations of  alleles  that are suited for the environment. 6

7. High and low genetic diversity In some cases, high levels of genetic diversity may be beneficial for a population or species, as it can lead to increased adaptability and resilience in the face of environmental changes. in other cases, low levels of genetic diversity may be advantageous , as they can help to maintain genetic purity and prevent the accumulation of harmful mutations. 7

8. steps to assess genetic diversity There are several steps that can be taken to assess genetic diversity and differentiation among populations, including: Defining populations : This involves assessing genetic differentiation or population structure  1 , which is typically the first step in identifying individuals or groups that can be compared for genetic diversity. Selecting genetic markers : This involves identifying the most informative markers, such as microsatellites or SNPs, for measuring genetic variation in the selected populations. Collecting and analyzing DNA samples: This involves collecting DNA samples from individuals within the selected populations and analyzing them for genetic variation using the selected genetic markers. Calculating diversity indices: This involves calculating standard diversity indices, such as heterozygosity or allelic richness, to quantify genetic diversity within and among populations. Assessing population differentiation: This involves calculating population differentiation indices, such as FST or GST, to quantify the degree of genetic differentiation among populations. Interpreting the results: This involves interpreting the results of the genetic analyses in light of the broader ecological and evolutionary context of the populations being studied. 8

9. markers used to asses genetic diversity and differentiation There are several markers used to assess genetic diversity and differentiation among populations including: Microsatellites , Single Nucleotide Polymorphisms (SNPs), Inter Simple Sequence Repeats (ISSRs), Amplified Fragment Length Polymorphism (AFLP) markers , and Nuclear Simple Sequence Repeats ( nSSRs ). These markers are commonly used in genetic studies to estimate population differentiation and quantify genetic diversity. The choice of marker used will depend on the specific research question and the type of organism being studied. 9

10. Metrics of genetic diversity and differentiation Genetic diversity of a population can be assessed by some simple measures. Gene diversity: is the proportion of polymorphic loci across the genome. Heterozygosity : is the fraction of individuals in a population that are heterozygous for a particular locus. Alleles per locus: is also used to demonstrate variability. Allelic richness: the number of different alleles present in a population. Nucleotide diversity: is the extent of nucleotide polymorphisms within a population, and is commonly measured through molecular markers such as micro- and minisatellite sequence s , mitochondrial DNA , and single-nucleotide polymorphisms (SNPs). 10

11. cont’d… Genetic diversity can also be measured. The various recorded ways of measuring genetic diversity include: F-statistics : measures of genetic differentiation between populations based on differences in allele frequencies. Pairwise fixation index (FST): a commonly used F-statistic that compares the genetic diversity within populations to the diversity between populations. Shannon-Wiener diversity index: a measure of both richness and evenness of alleles present in a population. Nei's genetic distance : a measure of genetic differentiation between populations based on the proportion of alleles shared between them. Species richness: is a measure of the number of species Species abundance: a relative measure of the abundance of species Species density: an evaluation of the total number of species per unit area 11

12. Effect of genetic diversity and differentiation Some studies suggest that high levels of genetic diversity can increase a population's adaptive potential and reduce the risk of inbreeding depression or susceptibility to disease. On the other hand, high levels of genetic differentiation between populations can limit gene flow and lead to the development of distinct adaptations or even new species . 12

13. End OF Slides!! Thank You!! 13