PCB 3063 Lecture Notes - Lecture 33: Null Allele, Epistasis, Zygosity

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2 Apr 2018

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A gene that is necessary for growth to a fertile adult. The products of essential genes are necessary for survival, and their absence results in lethality. Essential gene if a gene product is necessary for survival, but a single copy of the gene can provide sufficient amount, a null allele behaves as a ___________ ________ Recessive lethal (homozygotes die but the heterozygotes survive) A mode of inheritance in which phenotypic effects of two allelic genes are fully and simultaneiously expressed in the heterozygous individuals. True of false: the hypostatic locus alters the phenotypic expression of the epistatic locus. Occurs when two parents that exhibit a recessive phenotype yield offspring that exhibit the dominant phenotype for the character. True or false: complementation can only occur if the recessive mutant phenotypes of the two parents are caused by mutation in two different genes that affect the same character.

Related Questions

These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

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

PCB 3063 Lecture Notes - Lecture 33: Null Allele, Epistasis, Zygosity

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