BIOL204 Cons Gen Session 5

Question 1

What negative effects does genetic drift cause?

Answer 1

mildly deleterious alleles can reach fixation in small populations

Question 2

What is inbreeding?

Answer 2

the production of offspring from mating of individuals related by descent

Question 3

What are the negatives of inbreeding?

Answer 3

inbreeding increases the frequency of homozygotes and the expression of recessive deleterious alleles

Question 4

What is inbreeding depression?

Answer 4

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.

Question 5

What do pedigree coefficients show?

Answer 5

History of relatedness, often available in captive breeding programs

Question 6

Without a pedigree how can relatedness be shown?

Answer 6

Using Fis (the inbreeding coefficient) Measuring the observed heterozygosity Ho against the expected heterozygosity He

Question 7

A high expected heterozygosity can lead to?

Answer 7

Higher fitness, Rowe et al (1999)

Question 8

What is Heterosis?

Answer 8

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

Question 9

What is genetic rescue?

Answer 9

An increase in population fitness owing to immigration of new alleles.

Question 10

What is Outbreeding depression?

Answer 10

Reduced fitness of offspring from matings between genetically divergent individuals, owing to dilution of local adaptation and/or disruption of epistasis.

Question 11

2 benefits of Heterosis for genetic rescue?

Answer 11

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.

Question 12

What is epistasis?

Answer 12

interactions among genes at different loci that influence a phenotypic trait. Also that are not alleles

Question 13

why is increased homozygosity a problem? (2)

Answer 13

1. Dominance - the increased expression of deleterious recessive alleles in the population
2. Overdominance - where the heterozygous state has a fitness advantage.
   All leads to increased genetic load

Question 14

What is dominance in genetics terms?

Answer 14

the increased expression of deleterious recessive alleles in the population

Question 15

What is overdominance in genetic terms?

Answer 15

where the heterozygous state has a fitness advantage.

Question 16

When genetic dominance becomes a problem in a population, what is a risky conservation strategy to combat this? why is it risky?

Answer 16

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.

Question 17

why can’t you use purging as a conservation strategy for overdominance?

Answer 17

need both alleles for the increased fitness i.e. sickle cells and resistance to malaria. Can only purge for dominant mechanisms.

Question 18

How can we detect inbreeding? (2)

Answer 18

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)

Question 19

What are the different methods of measuring the pedigree coefficient? (2)

Answer 19

Path analysis or Gene drop analysis

Question 20

What is Fis again?

Answer 20

(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)

Question 21

Give 3 management options in the case of inbreeding

Answer 21

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.)

Question 22

What is fitness? and what are measure of fitness? (5)

Answer 22

Fitness: the capability of an individual (of certain genotype) to reproduce. 
Birth weight 
Parasite load
Seed germination
Growth rate
survivorship

Question 23

How does heterozygosity relate to the pedigree coefficient?

Answer 23

The lower the pedigree coefficient F the more genetic diversity.
Higher F or inbreeding = less heterozygosity

Question 24

What can we do when we discover problems due to inbreeding?

Answer 24

Genetic rescue, genetic restoration!
immigrants can infuse new genetic variation into local populations suffering from inbreeding depression and thus increase the mean population fitness

Question 25

Why do we need to be careful when using artificial translocation?

Answer 25

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)