1. Gene Variation
Chapter 6.6

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

3. 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

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

5. 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

6. 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

7. From where does genetic variation come?
min

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

9. Recombination From where does genetic variation come?
Shuffling gene variants (alleles) in a population

10. From where does genetic variation come?
Recombination

11. From where does genetic variation come?
Gene flow

12. Genetic drift From where does genetic variation come?

13. 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.

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

15. Effective population size - of Prokaryotes and Archaea?

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

17. 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.

18. How can natural selection act on a locus?

19. 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

20. 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.

21. 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

22. Bozeman Science – Gene Variation
genetic-variation