23 Inbreeding Depression Flashcards
What is the 6th mass extinction?
Currently happening
Human activities to blame
- Habitat destruction
- Fragmentation
- Poaching
- Hunting
Why is habitat destruction a threat to genetics?
Causes populations to become small and geographically isolated
Leading to genetic drift and inbreeding
What is genetic drift?
The process of losing genetic variation by chance
- Faster in small populations - tend to be less polymorphic
What caused declines in variation in Northern Elephant seals?
Were heavily exploited and hunted
- One population survived with possibly only one breeding male (pop has since recovered)
The recent severe bottleneck has led to decline in variation
Why are populations lacking in genetic variation more at risk?
They are less capable of evolving in response to new challenges
- High extinction risk
e.g. genetically homogenous populations more vulnerable to infection
What factors are related to extinction risk?
Environmental
Genetic
Why does inbreeding occur?
Fewer potential mates in small populations
- So probability of mating with relatives increases
What is Wright’s inbreeding coefficient (f)?
The standard measure of the degree of inbreeding of an individual
- f is the probability of inheriting two alleles that are identical by descent ( can range from 0-1)
If parents full siblings f=0.25
If parents are cousins f= 0.0625
What does identical by descent mean?
Two alleles are ibd if they trace their ancestry back to the same ancestral allele
- May be recessive alleles that cause a disease
What are the consequences of inbreeding?
- Inbred progeny have higher f values than outcrossed progeny
- Higher frequencies of homozygotes in inbred populations (reveals recessive deleterious alleles, less likely to benefit from heterozygote advantage)
- Inbreeding depression ( less fit than outcrossed progeny)
How might captive breeding programs cause inbreeding?
Endangered species often reared in captivity
Inevitably small populations
Some inbreeding may be unavoidable
Must ensure heterozygous carriers of recessive lethal alleles do not mate
Why does the incidence of some human diseases vary between populations?
A combination of selection and drift
e.g. Sickle-cell anaemia maintained in African populations by balancing selection
What is the aim of conservation genetics?
To reduce the loss of genetic variation and avoid inbreeding
How can isolated human populations be useful?
Used to map disease genes
- Good genealogical records
