Gene Variation Chapter 6.6

At what level do we study and compare genetic variation? Kingdom Phylum Class Order Family Genus Species Populations Individuals

What is genetic variation? Polymorphisms: Variation between individuals in a population (within species) Substitutions: Fixed variation between individuals of species (between species) Species B Species C Species A

What is genetic variation? Differences in the nucleotide sequence: Small scale: mutations in coding or non-coding DNA Protein alignment Hamster-Mouse-Human

Genetic variation within and between species Neutral rate of nucleotide substitutions and polymorphisms - Between species 1 and 2 - Within species 1 - Within species 2 Nucleotide variation in 25kb windows

Human and mouse genetic similarities Differences in the nucleotide sequence at large scale: structural differences across chromosomes 80 millions years Human and mouse genetic similarities Mouse chromosomes Human chromosomes Autosomes

From where does genetic variation come? https://www.youtube.com/watch?v=11iYk0Yrx3g 11 min

Mutations From where does genetic variation come? Base substitution mutation rate (10-9 bp/generation

Recombination From where does genetic variation come? https://www.youtube.com/watch?v=8rXizmLjegI Shuffling gene variants (alleles) in a population

From where does genetic variation come? Recombination

From where does genetic variation come? Gene flow

Genetic drift From where does genetic variation come? https://www.youtube.com/watch?v=FYbObPSKMwo

Effective population size Effective population size: Ne Ne is less than the actual number of potentially reproducing individuals! Sewal-Wrigth (1931) “The effective population size is the number of breeding individuals in an idealised population that show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration" When a new generation of animals is bred, the offspring gets half of its genes from the mother and the other half from the father. And when the number of fathers and mothers are large the H-W-equilibrium is ensured. Until now it has been implicit that we are dealing with the same number of individuals of each sex. In most cases of breeding with domestic animals this is not so. Normally only a few males are used in combination with many females. Thus the effective population size will be smaller than the actual size. The effective population size is based on the number of genes in the population that can be passed on to the next generation. This is assigned the symbol Ne (N-effective) and it has the formula: Four divided by N-effective equal 1 divided by the number of males plus 1 divided by the number of females.

Effective population size Sea urchins Strongylocentrotus purpuratus Wheat Triticum aestivum Tiger Panthera tigris

Effective population size - of Prokaryotes and Archaea?

KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

Sexual reproduction creates unique combinations of genes. Sexual reproduction creates unique combination of genes. independent assortment of chromosomes in meiosis random fertilization of gametes Unique phenotypes may give a reproductive advantage to some organisms.

How can natural selection act on a locus?

Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes. occurs during prophase I of meiosis I results in new combinations of genes

Chromosomes contain many genes. The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over. Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage. Genetic linkage allows the distance between two genes to be calculated.

Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes. occurs during prophase I of meiosis I results in new combinations of genes

Bozeman Science – Gene Variation http://www.bozemanscience.com/034-mechanisms-that-increase- genetic-variation