BIOL 3200 LEC 14

1) Why is genetic drift stronger in small populations?
Because random sampling has a larger effect when fewer individuals contribute genes to the next generation.

2) What allele frequency pattern suggests heterozygote advantage?
The allele frequency moves toward a stable intermediate equilibrium instead of fixation or loss.

3) If heterozygote advantage produces an equilibrium above 0.5 for allele A, what does that tell you?
AA is fitter than BB, but AB is the fittest genotype overall.

4) If an allele disappears and later reappears, what can explain that?
Drift followed by gene flow or a new mutation, but not selection alone.

5) What is a dominant-negative mutation?
A mutation where the mutant protein interferes with the function of the normal protein

6) What is a bottleneck?
A sharp reduction in population size that causes strong genetic drift and loss of genetic variation.

7) Why does a bottleneck reduce genetic diversity?
Because only a small random sample of the original population survives and reproduces.

8) Did humans likely experience bottlenecks in their evolutionary history?
Yes. The lecture says humans almost certainly went through several bottlenecks.

9) Does a population need to be small today to show founder effects?
No. It may be large now but still carry the genetic signature of being small in the past.

10) Name examples of recent founder-effect populations mentioned in the lecture.
Ashkenazi Jews, Iceland, and French Canada.

11) Why are the Amish a good population for genetic studies?
Because they are a founder population with large family sizes, restricted mating, and excellent genealogical records.

12) About how many founders gave rise to the Lancaster Amish population?
About 750 founders.

13) Why are Amish allele frequencies atypical compared with Europe?
Because of founder effects and additional drift after founding.

14) How many Amish live in Lancaster County according to the lecture?
Approximately 40,000.

15) What does the GRANDMA database show?
That the Amish have extremely detailed genealogical records useful for tracing ancestry and genetics.

16) Why are surnames on slide 18 an example of drift?
Because their frequencies changed randomly over generations, just like allele frequencies.

17) Why does the lecture mention Y chromosomes alongside surnames?
Because both are passed down the paternal line and can show similar drift patterns.

18) What does APOC3 normally do?
It encodes a product that slows down triglyceride breakdown.

19) What is the effect of the APOC3 truncating mutation in the Amish?
Faster triglyceride removal and lower heart disease risk.

20) Why is the APOC3 mutation more common in the Amish than in the general population?
Because drift increased its frequency after the founder event.

21) What does APOB do?
It encodes a protein needed for uptake of low-density cholesterol from the blood.

22) What happens when APOB has a loss-of-function mutation?
Risk of hypercholesterolemia increases.

23) What important lesson do APOC3 and APOB together teach?
Drift can increase the frequency of both advantageous and disadvantageous alleles.

24) What type of trait is Ellis–van Creveld syndrome?
A recessive trait.

25) Why is EvC much more common in the Amish than in the general population?
Because a rare allele carried by a founder drifted to higher frequency in the founder population.

26) What is the affected genotype frequency used in the lecture for EvC?
gAA = 0.005.

27) How do you calculate allele frequency p from the affected recessive genotype frequency?
p = √(gAA).

28) If p² = 0.005, what is p?
Approximately 0.07.

29) If p = 0.07, what is q?
0.93.

30) How do you calculate the carrier frequency?
gAB = 2pq.

31) Using p = 0.07 and q = 0.93, what is the carrier frequency?
About 0.13, or 13%.

32) Why are carriers much more common than affected individuals in recessive diseases?
Because rare recessive alleles are usually found in heterozygotes rather than homozygotes.

33) According to the lecture, are Amish genetic patterns mainly due to inbreeding?
No. They are mainly a textbook example of founder effects and genetic drift.

34) Why are isolated populations like Iceland useful for genetics?
Because founder effects and limited outside gene flow can make rare alleles easier to detect.

35) Why do cheetahs have such low genetic diversity?
Because they passed through severe bottlenecks.

36) About what proportion of cheetah loci are homozygous according to the lecture?
About 95%.

37) What famous observation shows how genetically similar cheetahs are?
Skin grafts between unrelated cheetahs can succeed without strong rejection.

38) What fertility problem is mentioned in cheetahs?
About 82% of sperm have abnormal morphology, and many males have low fertility.

39) What is a modern example of human-caused bottlenecks?
Overfished fish populations.

40) What happens to heterozygosity in bottlenecked populations?
It tends to decrease.

41) What is inbreeding?
Non-random mating between relatives.

42) What does “identity by descent” mean?
Two alleles are copies of the same ancestral allele.

43) What effect does inbreeding have on genotype frequencies?
It increases homozygosity and decreases heterozygosity.

44) Can inbreeding change genotype frequencies without changing allele frequencies?
Yes. That is one of its defining features.

45) Why is random mating important in Hardy–Weinberg equilibrium?
Because HWE assumes random mating; inbreeding violates that assumption.

46) According to the lecture, are the Amish highly inbred?
No. They avoid even cousin marriages, so they are less inbred than people often assume.

47) Why does inbreeding make recessive diseases more visible?
Because it increases the chance that recessive alleles become homozygous.

48) What historical examples of inbreeding are shown in the lecture?
The Blue Fugates, King Tutankhamun, and European royal families such as the Habsburgs.

49) What disease pedigree is shown on the final slide?
Hemophilia in European royal families.

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