4: Inbreeding and depression Flashcards
Name some human activities that are the blame for the 6th mass extinction
Habitat destruction
Fragmentation
Climate change
Poaching
Hunting
What is conservation genetics?
Habitat destruction → biggest threat to species
- Causes pop.s to become small and geographically isolated
- Decrease in genetic variation: Genetic drift, inbreeding
Conservation genetics is interested in remedying this
Describe genetic drift
Process of losing genetic variation, governed by pop. size
Plays important role in evo
Loss of genetic variation faster in smaller pop.s
= more severe in smaller pop.s
Describe genetic drift in the Northern/Southern Elephant seal
- Northern, once abundant but heavily exploited - almost extinct by 1900
- Southern exploited but always abundant = higher genetic variability
- One Northern pop. survived (20-30 indvids), now over 100,000 worldwide
Heterozygosity in Northern = 0.00026
Heterozygosity in Southern = 0.028
= heterozygosity in Northern pop.s 100-fold lower = due to genetic bottleneck
Does a decline in genetic variation matter?
Small pop.s do have less genetic variation
Pop.s that are small.lack genetic variation less capable of evolving in response to new challenges = high extinction risk
Give an example of how genetic variation links to extinction risk
Glanville fritillary butterfly, Finland
- 42 pop.s monitored, 7 went extinct
- examined factors that affect extinction risk:
= found that genetically more variable pop.s had a better chance of survival
Define inbreeding, what sort of pop. is it more common in?
mating between close relatives
Small pop.s have fewer potential mates = so probability of mating with relatives increases
Describe Wrights inbreeding coefficient
(f) → standard measure of the degree of inbreeding of an individual
2 alleles are identical by descent (ibd) if they trace their ancestry back to the same ancestral allele
f can range from 0-1
What is wrights inbreeding coefficient if:
- Parents are full sibs
- Parents are cousins
If parents are full sibs f = 0.25
If parents are cousins f = 0.0625
What are the consequences of inbreeding?
- Higher f values, if alleles at a locus are ibd the locus must be homozygous
- Higher frequencies of homozygotes
= Increase in recessive disorders (E.g CF)
= less likely to benefit from heterozygote advantage (E.g Kuru) - Inbreeding depression
Describe inbreeding in captive breeding programs + an example
When endangered species are reared in captivity, pop. inevetably low so some inbreeding unavoidable
E.g Californian Condor (largest North American bird)
- captive breeding program increased pop. from 27 to 150-200
- But recessive lethal allele has reached high frequency = homozygotes suffer a form of dwarfism (die at hatching)
- Programs must ensure heterozygotes do not mate together
Give an example of a conservation effort that has avoided the effects of small pop. size
Florida panther
- once down to a pop of only 60-70
- Road kill main cause of death = building tunnels under highways reduced the problem
- Remaining problem: persistent inbreeding means that most males suffer from cryptorchidism (undescended testes) → poorest sperm quality of any cat species
Solution:
- Introduced 6-8 females from a closely related subspecies in Texas
32 surviving progeny are known to be alive, robust and breeding
Give an example of a badly designed recovery program
- Koalas, used to be hunted for sport. By 1930s gone from S Australia
- Surviving individuals from Kangaroo island used to repop S. Australia
- A succession of bottlenecks caused a 50% reduction in genetic diversity (compared to N. Aus) and high frequency of missing testicles
Describe the effect of inbreeding on Amish pop.s in North America
- Small founder pop. from Rhineland, germany
- Marriage outside community is forbidden = inbreeding
- Excellent genealogical records - pedigrees used to understand inheritance
- High incidence of some disorders e.g Ellis-van Creveld syndrome (dwarfism, polydactyly, heart defects)
