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 A
Species B
Species C
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
0.14
Nucleotide variation in 25kb windows
0.12
0.1
0.08
0.06
0.04
0.02
0
Neutral rate of nucleotide substitutions and polymorphisms
- Between species 1 and 2
- Within species 1
- Within species 2
Differences in the nucleotide sequence at large scale: structural differences across chromosomes
Human and mouse genetic similarities
Mouse chromosomes
Human chromosomes
80 millions years
From where does genetic variation come?
https://www.youtube.com/watch?v=11iYk0Yrx3g
11 min
From where does genetic variation come?
Base substitution mutation rate (10-9 bp/generation
Mutations
https://www.youtube.com/wat
ch?v=GieZ3pk9YVo&feature=yo
utu.be mutations
From where does genetic variation come?
Recombination
Shuffling gene variants (alleles) in a population
https://www.youtube.com/watch?v=8rXizmLjegI
From where does genetic variation come?
Recombination
From where does genetic variation come?
Gene flow
From where does genetic variation come?
Genetic drift
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"
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-increasegenetic-variation