Term
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Definition
| All chromosomes are doubled (2n -> 4n -> 8n, etc.) |
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Term
| Conditions for Hardy Weinberg to work |
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Definition
1. Large population (>500 individuals)
2. Random mating
3. Closed population (no (e)migration))
4. No selection - all genotypes are equally successful
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Term
| Hardy Weinberg Equilibrium |
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Definition
For a population satisfying the 4 conditions:
p^2 + 2pq +q^2 = 1
p= freq. of A1
q = freq. of A2
p^2 = freq. of A1A1
2pq = freq. of A1A2
q^2 = freq. of A2A2
p and q are constant over time |
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Term
| H-W with 3 alleles A1, A2, A3 |
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Definition
Equation: p^2 + 2pq + 2pr + q^2 + 2qr + r^2 = 1
p+q+r = 1
p^2 = freq. of A1A1
2pq = freq. of A1A2
2pr = freq. of A1A3
q^2 = freq. of A2A2
2qr = freq. of A2A3
r^2 = freq. of A3A3 |
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Term
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Definition
Females follow the standard equation (p^2 + 2pq + q^2 = 1) due to receiving 2 X chromosomes
Males follow p+q = 1 due to only receiving one X since Y is not assoc. with many sex-linked diseases
i.e if q = 0.01, q^2 = 0.0001, making females much less likely to have a sex-linked recessive disorder i.e hemophilia than males (q = 0.01) |
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Term
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Definition
H-W does not stand up for a population when:
Conditions are violated (small population, nonrandom mating i.e interbreeding, etc.)
Interbreeding: Heterozygote proportion goes down while homozygote proportions go up
Self-fertilization (interbreeding): Probability of heterozygotes is halved with each generation
Sibling interbreeding: Probability of heterozygotes is cut by 1/4 for each generation
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Term
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Definition
| Inbreeding increases the frequency of a homozygous recessive phenotype with deleterious effects; accumulation of these deleterious effects often has a negative impact on population |
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Term
| How do zoos minimize inbreeding, especially among rare/endangered species? |
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Definition
| Zoos trade rare and endangered animals around to mate them with those of other zoos to prevent inbreeding |
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Term
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Definition
| Crossbreeding two inbred families so the resulting generation will be even more heterozygous (no real chance of disease or negative effects) than H-W (complete heterozygosity). Crossing two members of this 'super generation' returns the family to H-W and hybrid vigor ends |
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Term
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Definition
Random changes in allele frequency; severity increases as population size decreases
In small populations, with time, as breeding (especially interbreeding) progresses, alleles are lost (hence the change in p and q) and homozygosity increases from generation to generation
p and q do not remain constant due to sampling error caused by small population (only a 'few' copies of each allele can be measured, skewing the ratio of p and q)
If an allele is lost, that locus undergoes fixed monomorphism
Genetic drift vs. inbreeding: Both increase homozygosity at the expense of heterozygosity, but genetic drift changes p and q while they remain constant in inbreeding |
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Term
| Genetic Drift in the N. Elephant Seal |
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Definition
N. Elephant Seal- abnormally low genetic variation, high monomorphism (for a mammal)
Now: Live on Pacific coast in relatively large numbers
Subject to population bottleneck (large pop. may experience a sudden, temporary decline in size), causing temporary genetic drift with effects lasting even after/if the bottleneck ends (only alleles propagated during genetic drift remain); possible inbreeding due to small population size
Pre-1800s: Many seals
1800s: Hunted, mainly for blubber (1890: <20 left)
Today: ~130k, but little genetic variation due to genetic drift |
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Term
| Genetic Drift in the Cheetah |
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Definition
Cheetah- low genetic variation, possibly due to population bottleneck as a result of being hunted/ habitat destruction; cheetahs have problems breeding in zoos
High rate of sterility, poor immune system |
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Term
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Definition
Founder Effect - A few individuals from a population start a new population with different p and q than the original; inbreeding occurs for the first 1-2 generations if the founding population is small enough
Habitat Destruction (Gr. Prairie Chicken) - IL 1993 chickens: 3.7 alleles/locus, <50% egg hatch rate; elsewhere: >5 alleles/locus, >90% hatch rate (esp. the W. Midwest)
Birds were collected from W. populations and introduced to the IL population; caused an increase in population, genetic variation, hatch rate which lessened the effect of genetic drift |
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