BIOL 123 Lecture Notes - Lecture 10: Low Frequency, Allele Frequency, Heterozygote Advantage

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brownherring985

1 Jan 2021

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Bacteria = useful for running evolution experiments because their haploid genetics are relatively simple: selection = more complex in diploid due to interactions between 2 alleles at each genetic locus. Dominant allele will overshadow the other allele at the same locus. Recessive allele can affect the phenotype when paired with another copy of the same recessive allele. Rare recessive alleles are almost always carried in heterozygous individuals. Recessive alleles don"t affect the phenotype of heterozygotes = they remain hidden from action of selection. Positive allele = selection can increase frequency. Selection on deleterious recessive alleles: high frequency of heterozygotes = produce recessive homozygotes that start to suffer from lowered fitness = less common allele, low frequency = heterozygote state = hidden once more from selection. Selection on dominant alleles: right from the start it is exposed to selection, if favorable = spreads rapidly in populations (because rest of population carried the ancestral allele at that locus)

Related Questions

Differentiate amongcomplete dominance, incomplete dominance andco-dominance.

3. Understand an allelicseries -How many possible alleles are there for any given gene? Isthere only one recessive allele for a gene? Is there only onedominant allele for a gene? Is an allele always recessive ordominant with respect to other alleles of the gene?

4. What is a lethalallele? Are lethal alleles usually dominant or recessive? Are thereany exceptions? (Hint: Huntington disease in humans). How do wemaintain stocks with lethal alleles?

5. How can you tell if anallele is lethal? If one of the parents has a lethal allele, wouldall the possible genotypes be present in the progeny? What wouldhappen to the phenotypic ratios of the progeny?

6. What ispleiotropy?

7. How can you tell if atrait is determined by more than one gene? What ratios ofphenotypes in the F2 generation would you expect if a trait isdetermined by a single gene?

8. What is epistasis? Howcan the genotype at a locus affect the phenotype determined by thegenotype at another locus? What are complementary gene action,duplicate gene action, dominant suppression, dominant epistasis,and recessive epistasis?

skyrat774

QUESTION 1

Jim is blood type A, his brother John is type O and his sister Jane is type AB. What are the genotypes of their parents?

Which of the following is true for alleles that show incomplete dominance?

Heterozygotes have a genotype like the dominant allele.

Homozygotes have a genotype like the recessive allele.

Heterozygotes have a phenotype intermediate between the dominant and recessive alleles.

Homozygotes have the same phenotype as the heterozygotes.

QUESTION 3

Which principle of inheritance concluded that when games are formed in meiosis, the two alleles of each gene separate from one another, and each gamete receives only one allele?

independent assortment

Which term best describes a condition in which alleles at one locus can alter the expression of alleles at another locus?

polygenic inheritance

A single unit of genetic information located on a chromosome defines:

The physical expression (appearance or function) of an organism's genes defines:

genotype

a single characteristic

Palomino horses (golden color with a blond mane) are an incompletely dominant trait produced by the combination of the chestnut color allele and the cream color allele. If you wanted to produce as many palominos as possible, which mating strategy below would be the best choice?

Which term best describes the effect of a single gene on multiple aspects of the phenotype?

polygenic inheritance

QUESTION 9

Which term best describes the separate expression of both alleles for a single trait in the same cell?

polygenic inheritance

QUESTION 10

One form of a gene found on a single chromosome defines:

A chocolate lab (whose mother was a yellow lab) is mated with a black lab whose genotype is BbEe. What fraction of the offspring would be expected to be yellow labs?

What type of allele is always expressed regardless of whether the individual is homozygous or heterozygous for it?

Both the dominant and recessive alleles

Given the parents AABBGgHhrr Ã AabbGgHhRr, assume simple dominance and independent assortment. What proportion of the progeny will be expected to have the genotype AaBbggHHrr?

___________________ is defined as having two of the same type of allele for a particular trait.

The physical position of an allele on a single chromosome defines:

Which term best describes two or more genes affecting the phenotype in an additive fashion?

codominance

polygenic inheritance

GENETICS : You perform a dihybrid cross between two dogs that are each BbFf. Where not specified otherwise, assume black fur B is completely dominant to white fur b and furry F is completely dominant to hairless f

1. What genotypes at one locus will be epistatic to what genotypes at the other locus, if hair color and hair presence were the only measured phenotypes? (you may find it helpful to write out the genotypes and the phenotypes each would produce, and remember that epistasis is involved in this question).

What phenotypic ratios would you expect in the following scenarios (assume, unless otherwise noted, that the epistasis in part 1 still applies)?

2. Black B is completely dominant to albino b, furry F is completely dominant to hairless f

3. Black displays incomplete dominance to albino , and furry is codominant with hairless

4. Animals that are heterozygous at either locus are black and furry, overriding the other locus' geneotype

5. The black allele B displays epistasis when present at even one copy that masks the effects of the hairless f allele

6. It takes two black B alleles to mask the effects of the hairless f allele

7. Both the black alleles B and furry alleles F are lethal in their homozygous dominant states

8. Both the albino alleles b and hairless alleles f are lethal in their homozygous recessive states

9. Female dogs die when they have homozygous recessive or homozygous dominant states for either locus (dogs use XY inheritance for sex like we do). Note sex of doss in your phenotype ratios.

10. The black allele B although completely dominant, is the only 70% penetrant in heterozygotes and is 90% penetrant in homozygotes for the B allele

11. The hairless allele f is dominant in males and recessive in females

BIOL 123 Lecture Notes - Lecture 10: Low Frequency, Allele Frequency, Heterozygote Advantage

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