BIO 222 Chap 5: Incomplete Dominance and Codominance

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Questions and Answers

In a scenario exhibiting incomplete dominance, if a red-flowered plant (RR) is crossed with a white-flowered plant (WW), what would be the expected phenotype of the F1 generation?

All white flowers

All pink flowers (correct)

All red flowers

50% red, 50% white flowers

Which of the following best describes codominance?

The heterozygote expresses a phenotype that is intermediate between both homozygous phenotypes.

The heterozygote phenotype is masked by the dominant allele.

The heterozygote expresses both homozygous phenotypes simultaneously. (correct)

The heterozygote expresses the same phenotype as one of the homozygous phenotypes.

A plant with genotype $Aa$ shows the same phenotype as the plant with genotype $AA$. This is an example of:

Incomplete dominance

Overdominance

Codominance

Complete dominance (correct)

What proportion of progeny will be white if an F1 eggplant (Figure 5.2) is used in a testcross?

1/2 (C) Signup and view all the answers

A certain species of bird can have blue feathers (BB), white feathers (bb), or speckled feathers (Bb). If this is an example of codominance, what offspring would you expect from a cross between two speckled birds?

1 blue: 2 speckled: 1 white (D) Signup and view all the answers

Consider a gene that affects the color of roses. The R allele produces red roses, while the r allele produces white roses. However, when a red rose plant (RR) is crossed with a white rose plant (rr), the offspring (Rr) produce pink roses. What type of inheritance pattern does this represent?

Incomplete Dominance (D) Signup and view all the answers

In cystic fibrosis, heterozygotes produce enough functional CFTR protein to prevent the disease, while homozygotes for the mutated allele develop cystic fibrosis. Which type of dominance best explains this?

Complete dominance (C) Signup and view all the answers

How does the level of phenotype expression sometimes affect the determination of dominance?

It can obscure the true relationship between genotype and phenotype, leading to misinterpretation of dominance patterns. (D) Signup and view all the answers

In a scenario demonstrating codominance, what would be the expected phenotype of a heterozygote?

Simultaneous expression of both homozygous phenotypes. (B) Signup and view all the answers

In corn plants, if a cross between two green corn plants yields 2/3 green progeny and 1/3 yellow progeny, what is the most likely genotype of the green progeny?

Ww (A) Signup and view all the answers

Consider a plant species where incomplete dominance governs flower color. A cross between a red-flowered plant (RR) and a white-flowered plant (WW) yields offspring with pink flowers (RW). If two pink-flowered plants are crossed, what proportion of the offspring is expected to have the red phenotype?

25% (B) Signup and view all the answers

At a particular locus, there are five possible alleles. How many distinct genotypes are possible in a population?

15 (C) Signup and view all the answers

What is the key difference between penetrance and expressivity in genetics?

Penetrance refers to the percentage of individuals with a genotype expressing the expected phenotype, while expressivity describes the degree to which the trait is expressed. (D) Signup and view all the answers

Incomplete penetrance means that:

some individuals with a particular genotype do not express the corresponding phenotype. (A) Signup and view all the answers

How does gene interaction fundamentally differ from dominance?

Gene interaction involves genes at multiple loci affecting a single phenotype, while dominance involves interactions between alleles at a single locus. (B) Signup and view all the answers

How does incomplete dominance differ from incomplete penetrance?

In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype. (D) Signup and view all the answers

The F2 generation of a cross shows a phenotypic ratio of 9:3:3:1 for a particular trait. What does this suggest about the underlying genetic control?

Two genes are interacting to determine a single trait. (C) Signup and view all the answers

What is the primary effect of epistasis on gene expression?

It causes a gene at one locus to mask the effect of a gene at another locus. (C) Signup and view all the answers

A cross between two green corn plants yields 2/3 progeny that are green and 1/3 progeny that are yellow. What is the likely genotype of the green progeny, assuming that 'W' represents the allele for green color and 'w' represents the allele for yellow color, and that the homozygous recessive is lethal?

Ww (D) Signup and view all the answers

How does the phenotypic ratio in the F2 generation differ when gene interaction produces novel phenotypes compared to a standard dihybrid cross involving two independently assorting traits?

The F2 ratio in a dihybrid cross is always 9:3:3:1, while the ratio in gene interaction involving novel phenotypes can vary but involves only one trait. (B) Signup and view all the answers

A researcher observes a population of butterflies where wing color is determined by a single gene with two alleles: $C^R$ (red) and $C^W$ (white). Heterozygous individuals ($C^RC^W$) display a roan phenotype, with patches of both red and white scales on their wings. This is an example of:

Codominance (A) Signup and view all the answers

A particular allele is known to be lethal in homozygous form. A cross is performed between two heterozygous individuals. What ratio of viable offspring genotypes would you expect to observe?

2:1 (D) Signup and view all the answers

In a scenario where a single trait is determined by the interaction of genes at multiple loci, what observation would suggest that the genes involved assort independently?

An F2 phenotypic ratio of 9:3:3:1. (D) Signup and view all the answers

What is the key characteristic shared by multiple alleles?

More than two alleles exist for a given locus within a group of individuals. (C) Signup and view all the answers

In a cross involving all-white cats, the progeny are 12/16 all-white, 3/16 black, and 1/16 gray. Assuming two genes are involved, what is the most likely genotype of the gray progeny?

aa bb (D) Signup and view all the answers

Two white cats are crossed. White is the expected phenotype caused by the presence of at least one dominant allele. The offspring ratio is 12/16 white, 3/16 black and 1/16 grey. The offspring displaying the black phenotype must have what genotype?

A_ bb (D) Signup and view all the answers

In complementation testing, why is it crucial to use parents that are homozygous for different mutations?

To ensure the offspring are heterozygous, allowing for the observation of dominant phenotypes. (C) Signup and view all the answers

What outcome of a complementation test involving two recessive mutations would indicate that the mutations are allelic (occur at the same locus)?

All offspring exhibit only the mutant phenotype. (C) Signup and view all the answers

Brindle coloration is a recessive trait in both bulldogs and Chihuahuas. To investigate if the brindle genes in these breeds are at the same locus, which cross would be most informative?

Cross a homozygous brindle bulldog with a homozygous brindle Chihuahua. (B) Signup and view all the answers

In recessive epistasis, what is the resulting F2 phenotypic ratio from a dihybrid cross?

9:3:4 (B) Signup and view all the answers

Which of the following phenotypic ratios in the F2 generation indicates dominant epistasis?

12:3:1 (D) Signup and view all the answers

What F2 phenotypic ratio is characteristic of duplicate recessive epistasis?

9:7 (C) Signup and view all the answers

In Labrador retrievers, coat color is determined by recessive epistasis. If black is dominant (B) and brown is recessive (b), and another gene (E/e) determines if any pigment is deposited, what genotypes would result in a yellow lab?

Bbee and bbee (A) Signup and view all the answers

Consider a scenario where fruit color in squash is controlled by dominant epistasis. If white (W) is dominant to yellow (w), and another gene (Y/y) determines whether any color is produced (yellow if present), what phenotypic ratio would you expect in the F2 generation from a dihybrid cross?

12 white : 3 yellow : 1 green (B) Signup and view all the answers

Two genes, A and B, control a particular trait. A dihybrid cross (AaBb x AaBb) yields a 9:7 phenotypic ratio in the F2 generation. What type of gene interaction is likely occurring?

Duplicate recessive epistasis (D) Signup and view all the answers

In a plant species, purple flower color requires two dominant alleles, A and B. Plants with at least one recessive allele at either locus have white flowers. If you cross two heterozygous plants (AaBb), what phenotypic ratio of purple to white flowers do you expect in the F2 generation?

9 purple : 7 white (B) Signup and view all the answers

Consider a plant where the presence of at least one dominant allele of either gene A or gene B results in a round fruit, while the double recessive (aa bb) results in an oval fruit. If you cross two dihybrid plants (AaBb x AaBb), what phenotypic ratio would you expect to see in the offspring?

15 round : 1 oval (D) Signup and view all the answers

Which of the following best describes a trait determined by a genetic maternal effect?

The trait is determined by the nuclear genotype of the maternal parent. (C) Signup and view all the answers

A characteristic is more readily expressed in one sex, but the genes are located on autosomes. What type of genetic phenomenon is this?

Sex-influenced characteristic (A) Signup and view all the answers

Consider a trait that appears only in males, even though the responsible gene is located on an autosome. What type of inheritance pattern is likely at play?

Sex-limited inheritance (A) Signup and view all the answers

Genomic imprinting is an epigenetic phenomenon where the expression of a gene depends on its parental origin. Which epigenetic mark is primarily responsible for this?

DNA methylation (C) Signup and view all the answers

Which of the following is the most accurate description of 'anticipation' in genetics?

The stronger or earlier expression of a genetic trait in succeeding generations. (D) Signup and view all the answers

What is the underlying cause of anticipation in genetic traits across generations?

Expansion of unstable DNA regions. (D) Signup and view all the answers

A certain allele produces a functional protein at 30°C but a non-functional protein at 40°C. What kind of allele is this?

Temperature-sensitive allele (A) Signup and view all the answers

A scientist is studying a temperature-sensitive allele in fruit flies. At 25°C, the flies develop normal wings, but at 35°C, they develop deformed wings. If the scientist shifts the flies from 35°C back to 25°C during early development, what is the most likely outcome?

The flies will develop normal wings, as the normal protein function is restored at the lower temperature. (C) Signup and view all the answers

Flashcards

Allele

A version of a gene located at the same locus.

Complete Dominance

Heterozygote phenotype matches one homozygote's phenotype.