Question 1

The alleles that control which blood group antigens appear on the surfaces of red blood cells are

Accepted Answer

The alleles that control blood group antigens on red blood cells are codominant, which means that both alleles contribute equally to the phenotype. This is why individuals with the AB blood group have both A and B antigens present on their red blood cells.

Question 2

Mendel's results and conclusions were accurate,but are seen differently today,because we now realize that

Accepted Answer

Today, we know that single-gene traits are usually influenced by environmental and other genes, as well as genetic variation. This means that Mendel's conclusions, based on simple patterns of inheritance, are not always accurate when looking at more complex genetic interactions.

Question 3

Marbles is a Manx cat whose tail is so short that she appears not to have one.The genotype for short tail in Manx cats is heterozygous (Mm).Cats that are genotype mm have normal length tails,but cats that are genotype MM die before birth due to very abnormal brains and spinal cords.Marbles has one copy of a recessive _____ allele.

Accepted Answer

Marbles has one copy of the recessive allele that causes normal tail length (mm), which means she also has one copy of the dominant allele for short tail (M). However, if a cat has two copies of the dominant allele (MM), it will not survive due to lethal effects on brain and spinal cord development. Therefore, the recessive allele is lethal in the homozygous state.

Question 4

Epistasis and multiple alleles differ in that

Accepted Answer

Epistasis involves an interaction between two genes, while multiple alleles refer to the presence of more than two versions (alleles) of a single gene. Option A is incorrect because epistasis can occur between genes on the same chromosome. Option C is incorrect because sex does not determine the occurrence of epistasis or multiple alleles. Option D is incorrect because epistasis can occur in genes with only two alleles. Option E is incorrect because in some cases, one allele can mask the effect of another (e.g. dominant vs recessive alleles).

Question 5

Multiple alleles are common because

Accepted Answer

Multiple alleles are common because a gene sequence can vary in different ways and still encode a functional protein. In other words, different versions of a gene (alleles) can exist that result in slightly different protein products while still allowing for normal function. This is why we see a variety of traits and phenotypes in a population.

Question 6

Several members of the Fitzsimmons family have polydactyly,and they differ in their numbers of extra fingers and toes.Yet certain relatives who should have extra digits don't,such as Megan Fitzsimmons.She has two children,a son with two extra fingers and a daughter with an extra toe,and her father has an extra digit on each hand and foot.Polydactyly is

Accepted Answer

The varying expression and incomplete penetrance of polydactyly is illustrated by the differing number of extra digits among family members and the absence of extra digits in some relatives who should have them based on their familial history of polydactyly.

Question 7

Familial hypercholesterolemia illustrates incomplete dominance in humans because

Accepted Answer

Familial hypercholesterolemia is a genetic disorder that affects the body's ability to remove low-density lipoprotein (LDL) cholesterol from the blood. The disorder is caused by mutations in the LDL receptor gene, which leads to decreased functional LDL receptors on liver cells. This results in elevated levels of LDL cholesterol in the blood, which can lead to heart disease. Incomplete dominance is observed in heterozygotes with familial hypercholesterolemia because they have an intermediate number of LDL receptors on their liver cells, which results in an intermediate phenotype (i.e., intermediate LDL cholesterol levels) compared to homozygous wild type individuals (normal phenotype) and homozygous mutant individuals (severe phenotype).

Question 8

Some combinations of recessive alleles cause problems so severe that the fetus ceases to develop.Such lethal allele combinations appear to alter Mendelian ratios because

Accepted Answer

Homozygotes for the lethal allele do not survive to be counted in the progeny, thus altering the expected Mendelian ratios.

Question 9

If allele T (long tongue)exhibits incomplete dominance over the recessive allele t (short tongue),a heterozygote for this gene would most likely have

Accepted Answer

In incomplete dominance, the heterozygous individual shows an intermediate phenotype between the two homozygous traits. Therefore, a heterozygote for the long and short tongue gene would have a tongue of intermediate length.

Question 10

Zuzu is a white cat.She is genotype Ww for the "white masking gene" that reduces the number of melanocytes (pigment-containing cells).As a result,her body makes pigment,but it cannot get into the cells where it would color the fur.Zuzu's white masking gene is ______ to the melanin pigment gene because it prevents full expression of the pigment.

Accepted Answer

The term "epistatic" refers to a gene that can mask or interfere with the expression of another gene in a specific biological pathway, such as the production of melanin pigment. In this case, Zuzu's white masking gene is epistatic to the melanin pigment gene, because it prevents the full expression of the pigment even though it is present. The other choices (A, B, C, and E) are not relevant to this genetic scenario.

Question 11

Hairlessness in dogs is inherited from a single dominant allele.Inheriting two dominant alleles is lethal for the embryo.Ralph and Penelope are both hairless dogs.What is the probability that Penelope will give birth to a hairy puppy?

Accepted Answer

The answer of Hairlessness in dogs is inherited from a...

Question 12

Hairlessness in dogs is inherited from a single dominant allele.Inheriting two dominant alleles is lethal for the embryo.Penelope,a hairless dog,is wildly attracted to a hairy dog,Arnold.They mate.The probability that Arnold's sperm fertilizing Penelope's oocyte conceives a pup that would be hairless like Penelope is

Accepted Answer

Penelope is heterozygous (Hh) since two dominant alleles (HH) are lethal. Arnold is homozygous recessive (hh). The possible offspring are Hh (hairless) and hh (hairy), with a 1/2 probability of being hairless.

Question 13

When the cystic fibrosis gene was discovered in 1989,only one mutation was described,and a diagnostic test developed to detect it.Over the years,as more mutations were discovered,they were added to the test panel.Today,most pregnant women are offered a CF test that detects 100 or so alleles,although more than 1600 mutations have been discovered.These facts illustrate

Accepted Answer

The fact that over 1600 mutations have been discovered for the cystic fibrosis gene, but only 100 or so are detected in the current diagnostic test, indicates the presence of multiple alleles.

Question 14

The Addams family has an autosomal dominant condition in which webbing attaches the second toe to the third toe and the second toe is longer than the big toe.Only some of the Addams' who inherit the mutant allele have a second toe longer than the big toe.In addition,the extent of webbing varies.This phenotype is

Accepted Answer

The phenotype in the Addams family is variably expressive, meaning that the trait is expressed to varying degrees. Additionally, the phenotype is incompletely penetrant, meaning that not all individuals who inherit the mutant allele will express the trait. This is a common characteristic of autosomal dominant disorders.

Question 15

Can a woman with blood type A have a child with blood type O with a man who is AB?

Accepted Answer

The answer of Can a woman with blood type A...

Question 16

Morris is a big,healthy bull.One spring,he fathers ten calves,but five of them are stillborn,their muscles very rigid in a phenotype called "contracture." Three of the dams (mothers of the stillborns)are also Morris' daughters,and the fourth is his half-sister.Farm animals have little chance for romance and so often mate with their close relatives.The large number of stillborns is most likely due to

Accepted Answer

The large number of stillborns is likely due to multiple lethal alleles that Morris shares with his mates, as inbreeding increases the chance of offspring inheriting the same recessive lethal alleles from both parents.

Question 17

An example of an "outside the gene" influence is

Accepted Answer

Chemical groups that block or activate expression of certain genes are examples of epigenetic factors, which are influences outside the gene that affect gene expression.

Question 18

Brittany and Jarod have been trying to have a second child for 10 years.They have one healthy child,but Brittany has had four early spontaneous abortions.One explanation for the many pregnancy losses is that Brittany and Jarod

Accepted Answer

Brittany and Jarod having heterozygous for lethal alleles of the same gene can result in early spontaneous abortions. If both parents carry a copy of a lethal gene, there could be a 25% chance of their offspring inheriting two copies of the gene, resulting in a lethal outcome. This could explain the repeated pregnancy losses.

Question 19

A gene may have many alleles,but a person has only two alleles for a gene,because

Accepted Answer

A gene may have many alleles, but a person inherits only two alleles for a particular gene - one from their mother and one from their father. This is because a person has only two copies of each gene, one on each homologous chromosome. The number of possible alleles does not affect the number of alleles a person inherits for any given gene.

Question 20

Different alleles that are both expressed in a heterozygote are

Accepted Answer

Codominance occurs when both alleles are expressed equally in a heterozygote. Dominance occurs when one allele masks or suppresses the expression of the other allele. Incomplete dominance occurs when neither allele is dominant, and a blended phenotype is produced. Homozygous dominant refers to an individual with two identical dominant alleles, while automatically dominant is not a recognized genetic term.

Quiz 5: Beyond Mendels Law