Question 1

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

Accepted Answer

Homozygotes for the lethal allele do not appear as a progeny class, as they do not survive to reproduce and pass on the allele. This disrupts the typical 1:2:1 genotypic ratio observed in Mendelian genetics. Carriers (heterozygotes) may still appear in the progeny class, but they do not express the lethal phenotype. Therefore, option C is the correct choice.

Question 2

In Addam's family,there is 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 members who have inherited 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 Addam's family is variably expressive because not all individuals who inherit the mutant allele have a second toe longer than the big toe, and the extent of webbing varies. It is also incompletely penetrant because not all individuals who inherit the mutant allele express the phenotype. As a result, the condition is not completely dominant or recessive, and it can't be inherited and non-inherited.

Question 3

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

Accepted Answer

The alleles controlling A and B blood group antigens are codominant, meaning that both alleles are dominant and expressed equally if present. Therefore, if an individual inherits one A allele and one B allele, they will have both A and B antigens on their red blood cells. This is different from incomplete dominance or semidominance, where one allele is partially dominant over the other and results in an intermediate phenotype. Variably expressed alleles can result in different levels of expression of the trait, but this is not the case for A and B blood group antigens.

Question 4

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." Farm animals often mate with their close relatives.So,three of the dams (mothers of the stillborns)are also Morris' daughters,and the fourth is his half-sister.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 recessive lethal alleles being expressed.

Question 5

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 white masking gene is epistatic to the melanin pigment gene because it masks the expression of the pigment gene. This means that regardless of whether Zuzu has one or two copies of the pigment gene, her fur will still appear white due to the action of the white masking gene. This is different from a dominant or recessive gene, where the presence or absence of a particular allele would directly determine the phenotype.

Question 6

When the cystic fibrosis gene was discovered in 1989,only one mutation was described,and a diagnostic test was 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.Which of these is reflected by the given facts?

Accepted Answer

The fact that more than 1600 mutations have been discovered but only a smaller subset of 100 or so alleles are detected in the standard CF test indicates the presence of multiple alleles. Pleiotropy refers to a single gene affecting multiple traits, phenocopy refers to an environmental factor mimicking genetic expression, and lethal alleles are those causing premature death, none of which are indicated by the given facts.

Question 7

Different alleles that are both expressed in a heterozygote are

Accepted Answer

In codominance, each allele in a heterozygote is expressed fully and equally. Therefore, neither allele is dominant over the other, and both are expressed.

Question 8

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 heterozygote expresses a phenotype that is intermediate between the two homozygotes. Therefore, a heterozygote for the gene that controls tongue length would have a tongue of intermediate length.

Question 9

Familial hypercholesterolemia illustrates incomplete dominance in humans because

Accepted Answer

Familial hypercholesterolemia is caused by a mutation in the LDL receptor gene, leading to decreased uptake of cholesterol from the bloodstream. Heterozygotes for the disease have one mutated copy of the gene and one normal copy. This results in a reduced but still functional number of LDL receptors on their liver cells, leading to an intermediate level of cholesterol accumulation. This is an example of incomplete dominance, as the heterozygous phenotype is intermediate between the homozygous wild type and homozygous mutant phenotypes.

Question 10

Clara has alkaptonuria.Her symptoms include back spasms,dark urine,arthritis,hearing loss,kidney stones,heart valve damage,and darkened ear tips.This condition is therefore

Accepted Answer

Alkaptonuria is a pleiotropic genetic disorder. This means that it affects multiple organ systems and has a variety of symptoms, including those listed for Clara. It is caused by a mutation in the HGD gene, which leads to a deficiency in the breakdown of homogentisic acid. This results in the accumulation of homogentisic acid in the body, which causes the various symptoms of the disorder.

Question 11

Epistasis and multiple alleles differ in that

Accepted Answer

Epistasis is a type of gene interaction where the expression of one gene affects the expression of another gene. Multiple alleles are different versions of the same gene. Therefore, these two concepts differ in their basic definition and do not affect different sexes, nor is epistasis limited to genes that have multiple alleles. Additionally, while epistasis can mask the expression of another gene, a single allele cannot mask the effect of another allele, which is a property limited to dominant and recessive alleles.

Question 12

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 highly abnormal brains and spinal cords.Marbles has one copy of a dominant _____ allele.2-14-2013

Accepted Answer

Marbles has one copy of the heterozygous genotype for the short tail trait in Manx cats, which is a dominant lethal allele. This means that if Marbles had two copies of the dominant allele (MM), she would not have survived past birth due to abnormal brain and spinal cord development. The other answer choices are not applicable in this scenario.

Question 13

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 in this family is

Accepted Answer

The fact that some relatives with the polydactyly trait do not express it, such as Megan Fitzsimmons, suggests incomplete penetrance. The fact that different relatives have varying numbers of extra digits suggests variable expressivity. Therefore, the best choice is A, variably expressive and incompletely penetrant.

Question 14

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. This is due to the redundancy of the genetic code, where multiple codons can code for the same amino acid. Therefore, different variations of a gene can exist without affecting the function of the protein it encodes.

Question 15

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

Accepted Answer

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

Question 16

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

Accepted Answer

We now know that single-gene traits are often influenced by multiple genes as well as environmental factors, which can affect the expression of the trait. Therefore, Mendel's conclusions based solely on single-gene inheritance do not fully represent the complexity of genetic inheritance.

Question 17

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.The most likely explanation for the many pregnancy losses is that Brittany and Jarod

Accepted Answer

Brittany and Jarod are likely each heterozygous for lethal alleles of the same gene, which can result in spontaneous abortions when the fetus inherits two copies of the lethal allele.

Question 18

Hairlessness in dogs is inherited from a single dominant allele.Inheriting two dominant alleles is lethal for an embryo.Penelope,a hairless dog mates with Arnold,a dog with hair.The probability Penelope will have hairless puppies is

Accepted Answer

Penelope must be heterozygous (Hh) since two dominant alleles (HH) are lethal. Arnold is homozygous recessive (hh). The possible offspring are Hh (hairless) and hh (with hair), so the probability of hairless puppies is 1/2.

Question 19

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 20

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

Accepted Answer

Each person inherits one allele for a gene from each parent, resulting in two alleles per gene in a diploid cell. However, a gene may have many different alleles present in the population as a whole, but any given individual will only possess two of them. This is due to the fact that humans are diploid organisms with two sets of chromosomes, one inherited from each parent.

Quiz 5: Beyond Mendels Laws