BIOL204 Cons Gen Session 5 Flashcards
What negative effects does genetic drift cause?
mildly deleterious alleles can reach fixation in small populations
What is inbreeding?
the production of offspring from mating of individuals related by descent
What are the negatives of inbreeding?
inbreeding increases the frequency of homozygotes and the expression of recessive deleterious alleles
What is inbreeding depression?
A reduction in fitness of offspring of related individuals leading to decreased reproduction/survival (Charlesworth, 1987) owing to reduced heterozygosity and/or increased expression of deleterious, recessive alleles.
What do pedigree coefficients show?
History of relatedness, often available in captive breeding programs
Without a pedigree how can relatedness be shown?
Using Fis (the inbreeding coefficient) Measuring the observed heterozygosity Ho against the expected heterozygosity He
A high expected heterozygosity can lead to?
Higher fitness, Rowe et al (1999)
What is Heterosis?
Heterosis is when an F1 or first generation offspring has a higher fitness than its parents. For example a 10 and 8 meter snake producing a 15 meter snake. First coined by (Shull, 1914) Also known as hybrid vigour
What is genetic rescue?
An increase in population fitness owing to immigration of new alleles.
What is Outbreeding depression?
Reduced fitness of offspring from matings between genetically divergent individuals, owing to dilution of local adaptation and/or disruption of epistasis.
2 benefits of Heterosis for genetic rescue?
immigrant alleles can mask deleterious, recessive alleles that have achieved a high local frequency via genetic drift
matings between immigrants and local individuals produce highly heterozygous offspring, which are often favored by natural selection.
What is epistasis?
interactions among genes at different loci that influence a phenotypic trait. Also that are not alleles
why is increased homozygosity a problem? (2)
- Dominance - the increased expression of deleterious recessive alleles in the population
- Overdominance - where the heterozygous state has a fitness advantage.
All leads to increased genetic load
What is dominance in genetics terms?
the increased expression of deleterious recessive alleles in the population
What is overdominance in genetic terms?
where the heterozygous state has a fitness advantage.
When genetic dominance becomes a problem in a population, what is a risky conservation strategy to combat this? why is it risky?
Purging - not allowing individuals with the double recessives to breed.
Risky as you are also reducing the effective population and this may lead to extinction.
why can’t you use purging as a conservation strategy for overdominance?
need both alleles for the increased fitness i.e. sickle cells and resistance to malaria. Can only purge for dominant mechanisms.
How can we detect inbreeding? (2)
1) Pedigree inbreeding / pedigree coefficient - F, using the prob that alleles are identical by descent. Remember that genetically we expect full siblings or parent/offspring to share on average 50% of their alleles (r=0.5), half sibs 25%, and so on.
2) Hamiltons ‘r’, similar to pedigree but between pairs of individuals, a.k.a. kinship coefficient
3) Non-random mating - Fis (inbreeding coefficient)
What are the different methods of measuring the pedigree coefficient? (2)
Path analysis or Gene drop analysis
What is Fis again?
(the ‘inbreeding coefficient’)
The heterozygosity observed among individuals compared to what we’d expect for the subpopulation as a whole (He)
Varies from:
-1 (excess of homozygotes) to 1 (excess of heterozygotes)
Give 3 management options in the case of inbreeding
Avoid mating relatives, using knowledge of individual relatedness
Purging: the deleterious alleles can be selected back out of the population, in situations where homozygosity is an issue due to dominance. But risky!
‘Genetically rescue’ inbred populations where inbreeding depression is a real risk, where possible with individuals from other populations. (But may not be available.)
What is fitness? and what are measure of fitness? (5)
Fitness: the capability of an individual (of certain genotype) to reproduce. Birth weight Parasite load Seed germination Growth rate survivorship
How does heterozygosity relate to the pedigree coefficient?
The lower the pedigree coefficient F the more genetic diversity.
Higher F or inbreeding = less heterozygosity
What can we do when we discover problems due to inbreeding?
Genetic rescue, genetic restoration!
immigrants can infuse new genetic variation into local populations suffering from inbreeding depression and thus increase the mean population fitness
Why do we need to be careful when using artificial translocation?
can be a success but might not be as in the case of the Tatra mountain Ibex, they introduced a distant relative to form hybrids. They were adapted differently to their rutting season, rutted too early and offspring died (outbreeding depression). Now extinct. (Beibach & Keller, 2009)
