Topic 2

Question 1

how to model random mating

Answer 1

• In a Panmictic population, each female has an equal probability of mating with each male (and vise versa)
• a randomly mating population can be thought of as a pool of gametes, or a pool of alleles
• The probability that two gametes (alleles) unite to form a zygote (diploid genotype) is equal to the product of their frequencies (allele frequencies)

Question 2

HW expected genotypes

Answer 2

p^2+2pq+q^2=1

Question 3

what does the HW principle do?

Answer 3

• Given Allele frequencies in a parental generation, it allows us to calculate Expected Genotype Frequencies among their offspring, or next generation.

Question 4

Assumptions of the HW principle

Answer 4

1. Mating is Random (Panmictic)
2. Non- Overlapping Generations
3. Population is Diploid
4. Reproduction is strictly Sexual
5. Population is Very Large
6. Migration is Negligible
7. Genetic Mutations Don’t Occur
8. Unaffected by Natural Selection

Question 5

points about the HW principle

Answer 5

1. It shows that in the absence of violations of its assumptions, genotype and allele frequencies will be stable from one generation to the next (no evolution will occur since there will be no change in allele frequencies). As a result, we can use it to make inferences about the current generation
2. If for some reason a population is not in HW equilibrium (say we create a population by selecting genotypes in such a way that their frequencies deviate from Hardy-Weinberg expectations), it will take a single generation of random mating to restore the expected Hardy-Weinberg genotype frequencies

Question 6

domaniant vs recessive

Answer 6

• Refers to situations in which one allele has such strong phenotypic effects in heterozygotes that it conceals the effect of the weaker allele.
• In such cases, the stronger allele is said to be dominant, and the weaker allele is said to be recessive.

Question 7

deleterious recessive allele

Answer 7

• Result in reduced fitness (survival and reproductive success) when in homozygous form.
• Hence, they do not escape the “attention” of natural selection, and we cannot assume that the assumption of no selection is valid, as a result, the HW principle cannot be considered valid in these cases.

Question 8

HW disequilibrium

Answer 8

• HW disequilibrium is when observed genotype frequencies deviate from those expected using the HW principle.
• HW disequilibrium (or deviations) will always be a result of either a heterozygote deficit, or heterozygote excess.

Question 9

parthenogenesis

Answer 9

• “virgin birth” the development of an egg with no paternal contribution- female clonal reproduction

Question 10

obligate parthenogenesis

Answer 10

• species consists of females only; eggs never develop into males and there is never sexual reproduction

Question 11

cyclical parthenogenesis

Answer 11

• Males develop from eggs at some point, resulting in sexual reproduction, which produces an all-female population that reproduces clonally

Question 12

morphological species concept

Answer 12

• Individuals are considered to belong to the same species if they agree morphologically with the “Type” of the species

Question 13

biological species concept

Answer 13

• Species are groups of interbreeding natural populations that are reproductively isolated from other such groups

Question 14

morphologically cryptic species

Answer 14

• Cryptic biological species (sometimes called sibling species) can usually only be identified using genetic methods, and are extremely common

Question 15

what can cause HW disequilibrium

Answer 15

1. Natural Selection: Heterozygote excesses or deficits
2. Inbreeding: Heterozygote deficits
3. Outbreeding: Heterozygote excesses
4. Assortative mating: Heterozygote excesses or deficits
5. Asexual Reproduction: Heterozygote excesses or deficits
6. Cryptic species: heterozygote deficits
7. Gene flow and migration: Heterozygote excesses or deficits
8. Population Bottlenecks: Heterozygote excesses or deficits
9. Founder effects: Heterozygote excesses or deficits

Question 16

null alleles

Answer 16

• alleles that are present at microsatellite loci, but do not amplify in a PCR reaction (usually because of a poor primer match).
• Null alleles will give the appearance of a heterozygote deficit, when in fact a heterozygote deficit does not exist.
• When a null allele is present in a heterozygote and does not amplify in a PCR reaction, the heterozygote will appear to be a homozygote because only one allele amplifies- hence the appearance of a heterozygote deficit

Question 17

exception to HW principle (sex determination)

Answer 17

• Many diploid sexually reproducing organisms have an XY chromosome sex determination system.
• Humans: Males carry one X and one Y chromosome; females carry two X chromosomes. The Y chromosome only carries a few genes (mostly involving sex determination and male fertility). Genes (loci) located on the X chromosome are referred to as X-linked genes

Question 18

x-linked loci

Answer 18

• For an X-linked locus with 2 alleles (A and B), there are 3 possible female genotypes: AA, AB, and BB and two possible male genotypes: A and B

Question 19

deleterious x-linked recessive alleles

Answer 19

• A consequence of deleterious X-linked recessive alleles is that males will be affected by the resulting condition more often than females.
• This is illustrated by the frequency of colour blindness among males and females in humans