Cycle 6 Flashcards
How allele frequencies change within a population
Population genetics (evolutionary genetics/microevolution)
A ______ is a collection of families
population
T/F news: people with naturally blonde hair are going to go extinct/the apple associated with blonde hair in humans is most likely to go instinct by 2202
FALSE
The fake news stated that the problem is that blonde hair is caused by:
a recessive allele gene coding for hair color in humans
If we start with a common dominant allele (p=0.6) and a rarer recessive allele (q=0.4), with no selection, how will allele frequencies change?
A) The dominant allele will increase in frequency and the recessive allele will disappear
B) Allele frequencies will stabilize at 0.75 dominant, 0.25 recessive
C) Alllele frequencies will stabilize at 0.50 dominant, 0.59 recessive
D) Allele frequencies will not change
D) Allele frequencies will not change
When there is selection against a dominant allele, selection will:
remove every single copy of the dominant allele from the population
In the absence of selection, if all the genotypes are equally fit, the fact that the allele is a recessive DOES NOT or DOES change its frequency in the population
DOES NOT
The alleles______ ______ does NOT affect its frequency if there is no selection going on
dominance status
Simply being recessive in the absence of selection doesn’t affect allele _______
frequencies
Weaker selection would just take _____ to remove every copy of the dominant allele
longer
_______ will increase to a frequency of 1, ______ to 0
Recessive, dominant
Selection against the dominant allele increases or removes genetic variation?
Removes
under heterozygote advantage, is the population evolving?
Yes
Yes, at first, but not after allele frequencies stabilize
No
Yes, at first, but not after allele frequencies stabilize
Situations where there is no complete dominance: If there are two alleles at a locus, can have __ different phenotypes
3
This is because:
recessive alleles can hide in the heterozygotes
They are Sheltered by _____
diploidy
when there is selection against a recessive allele (dominant allele favored):
selection will not be able to remove every single copy of the recessive allele, the frequency will just decrease, but never 0
Selection is not as effective in this case:
Selection against a recessive allele (dominant allele favored)
If _____ is present, and genotypes differ in _____ then the dominant status of the allele does matter somewhat
selection, fitness
Most genetic disorders are almost always going to be associated with _______ alleles
recessive
Under heterozygote advantage, is the population experiencing selection?
Yes
Yes, at first, but not after allele frequencies stabilize
No
YES
T/F recessive alleles are not necessarily always harmful, selection just removes all the copies of harmful dominant alles
TRUE
______ would have a different phenotype than the homozygous
Heterozygous
Harmful alleles will always ______ in frequency, but whether it’s to zero depends on whether the harmful allele is dominant or recessive
decrease
______: situation where the genotypes differ in fitness
Selection
______: change in allele frequencies
Evolution
Can you have selection, without necessarily having evolution?
YES
Selection against homozygotes does or does not maintain long-term genetic variation
Does Maintain long-term genetic variation
In selection against _______: Doesn’t matter if you started with lots of copies of the dominant vs recessive allele
homozygotes
In Selection against heterozygote: Whichever allele started off more ____ will disappear
rare
In: Selection against homozygotes
Common allele decrease in frequency until it hits ___
0.5
Selection against heterozygotes Increases or Removes genetic variation
Removes
T/F Populations usually show clean “Mendelain” (1:2:1, 1:3:3:1) ratios of phenotypes or genotypes
FALSE: Populations DO NOT usually show clean “Mendelain” (1:2:1, 1:3:3:1) ratios of phenotypes or genotypes
BUT, just as for a single family, knowing the distribution of parental genotypes in a population lets us predict the distribution of genotypes in the:
next generation
_____ predicts the outcome of a cross between two parents and in a randomly-mating population
Punnet square
Conditions of Hardy-Weinberg Equilibrium (5)
Large
Random-mating population
Where mutations are very rare
And there is no migration (gene flow)
Or no selection
HWE formulas: freq of (A1A1) =
p^2
If HWE conditions met then: (2)
-Allele frequencies will not change
-Genotype frequencies can be predicted from allele frequencies
freq (A1A2) =
2pq
If not:
the population is NOT at HWE at this locus
One or more HWE assumptions are violated and the population could be evolving
freq (A2A2) =
q^2
3 steps:
1) Use observed genotype frequencies to calculate allele frequencies
2) Use these allele frequencies to calculate genotype frequencies that we’d expect under HWE
3) Compare observed vs expected numbers of each genotype: is the population in HWE at this locus?
is the population in HWE at this locus If observed and expected same: ___
YES
If genotype frequencies can be predicted from allele frequencies, the population is:
at HWE (it is not evolving) at this locus
Dominance status of an allele does not cause ______, but can affect response to selection
evolution
In a population of 100 pigs, there are 36 homozygous dominant black pigs (genotype BB), 48 heterozygous black pigs (BR), and 16 homozygous recessive red pigs (RR). What is the frequency of the R allele?
A : 0.64
B : 0.4
C : 0.32
D : 0.16
E : 0.08
B : 0.4
_______ principle helps identify whether a population might be evolving
Hardy-Weinberg
Is it likely that evolutionary agents are acting on this population at the tasting gene locus?
A : Yes
B : No
A : Yes
Different types of _____ have different effects on genetic variation; some remove alleles entirely, some maintain more than one allele at a locus
selection
Allele T, associated with the ability to taste a particular chemical, is dominant over allele t, associated with the inability to taste it. After surveying 100 people, 36 people can taste the chemical and 64 are non-tasters. The “tasting” gene was sequenced from all of the people who can taste the chemical, and the results show that 24 of the tasters are homozygous and 12 are heterozygous. What is the frequency of the T allele in this population?
A : 0.8
B : 0.6
C : 0.3
D : 0.2
C : 0.3
A population of peas has 4 % of individuals that have purple flowers because they are homozygous dominant for the A allele, and 32 % are light purple and heterozygous (AB). The rest of the individuals are white (BB). What is the frequency of the B allele?
A : 0.80
B : 0.72
C : 0.64
D : 0.32
A : 0.80
Is this population in Hardy-Weinberg Equilibrium?
A : Yes
B : No
A : Yes
