Question 1

In some parts of Africa, the frequency of individuals who are heterozygous for the sickle-cell anemia allele is higher than the frequency in North America, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following?

Accepted Answer

This relationship is an example of Darwin's theory of natural selection, where the heterozygous advantage for the sickle-cell allele in malaria-endemic regions of Africa leads to a higher survival rate of individuals with this genotype, thus increasing its frequency in the population.

Question 2

In rabbits, the homozygous genotype LCLC has straight legs, LCLc results in deformed legs, and LcLc results in very short legs. The genotype FBFB produces black fur, FBFb brown fur, and FbFb white fur. If a cross is made between brown rabbits with deformed legs and white rabbits with deformed legs, what percent of the offspring would be expected to have deformed legs and white fur?

Accepted Answer

The cross between brown rabbits with deformed legs (FBFb LCLc) and white rabbits with deformed legs (FbFb LCLc) will produce offspring with the following genotypes:FBFb LCLC (brown, straight legs)FBFb LCLc (brown, deformed legs)FbFb LCLC (white, straight legs)FbFb LCLc (white, deformed legs)The probability of getting offspring with deformed legs and white fur is 1/4 or 25%.

Question 3

Feather color in budgies is determined by two different genes, Y for pigment on the outside of the feather, and B for pigment on the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. Two blue budgies were crossed. Over the years, they produced 22 offspring, five of which were white. What are the most likely genotypes for the two blue budgies?

Accepted Answer

Given that two blue budgies produced white offspring (yybb), both parents must carry the recessive b allele to pass it on to their offspring. Since they are blue (yyBB or yyBb), the only genotype that allows them to produce white offspring (yybb) through their combination is yyBb for both, as this genotype can provide both the y and b alleles needed for white offspring.

Question 4

Skin color in a certain species of fish is inherited via a single gene with four different alleles. Each allele confers a unit of color darkness such that having allele S1 confers one unit of color, S2 has two units, S3 has three units, and S4 confers four units. A fish of this type has the genotype S1S3, and its mate has the genotype S2S4. What proportion of their offspring would be expected to have five units of color?

Accepted Answer

The answer of Skin color in a certain species of...

Question 5

Marfan syndrome in humans is caused by an abnormality of the connective tissue protein fibrillin. Patients are usually very tall and thin, with long spindly fingers, curvature of the spine, sometimes weakened arterial walls, and sometimes eye problems, such as lens dislocation. Which of the following would you conclude about Marfan syndrome from this information?

Accepted Answer

Marfan syndrome is pleiotropic because a single genetic mutation in the fibrillin gene leads to multiple phenotypic effects, such as tall stature, long fingers, spine curvature, arterial issues, and eye problems.

Question 6

An obstetrician knows that her patient's fetus is at risk for a serious disorder that is detectable biochemically in fetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?

Accepted Answer

Amniocentesis or chorionic villus sampling (CVS) are procedures used to collect fetal cells for biochemical and genetic testing, making them the most appropriate options for detecting a serious disorder in a fetus.

Question 7

Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. Also, a second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. The relationship between genes S and N is an example of which of the following inheritance patterns?

Accepted Answer

The relationship between genes S and N is an example of epistasis, where one gene (N) masks or modifies the expression of another gene (S).

Question 8

Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. A second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. If cacti heterozygous for both traits, SsNn, were allowed to self-pollinate, the offspring would segregate into which of the following phenotype ratios?

Accepted Answer

To determine the phenotype ratio, we use the dihybrid cross method. The genotype of the parent cacti is SsNn. When these cacti self-pollinate, the offspring can have the following genotypes and phenotypes: SSNN, SSNn, SsNN, SsNn (sharp-spined); ssNN, ssNn (dull-spined); and nn (spineless, regardless of the S gene because N is epistatic to S). The phenotypic ratio is 9 sharp-spined:3 dull-spined:4 spineless.

Question 9

Hutchinson-Gilford progeria is an exceedingly rare human genetic disorder in which individuals look very old even as young children, experience very early senility and severe coronary artery disease, and have a life expectancy of 13 years. Which of the following statements represents the most likely assumption regarding this disorder?

Accepted Answer

Hutchinson-Gilford progeria syndrome is caused by a mutation in the LMNA gene, which encodes for the lamin A protein. This mutation is not typically inherited but occurs as a new (de novo) mutation, explaining why it's rare and not often seen in multiple generations of the same family.

Question 10

Which of the following statements correctly explains the observation that parents with two different phenotypes produced offspring with a phenotype that is a blend of the two parental varieties?

Accepted Answer

This observation is explained by incomplete dominance, where neither allele is completely dominant over the other, resulting in a phenotype that is a blend of the two parental phenotypes.

Question 11

Feather color in budgies is determined by two different genes: Y for pigment on the outside of the feather, and B for pigment on the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. A blue budgie is crossed with a white budgie. Which of the following results in the offspring is most possible?

Accepted Answer

A blue budgie (yyBB or yyBb) crossed with a white budgie (yybb) can produce offspring that are either blue (yyBb) or white (yybb), depending on the alleles inherited from each parent.

Question 12

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The flower color trait in radishes is an example of which of the following inheritance patterns?

Accepted Answer

The cross between a red-flowered plant and a white-flowered plant yielding all-purple offspring is an example of incomplete dominance. In incomplete dominance, the phenotype of the heterozygotes is intermediate between the phenotypes of the two homozygotes, which is why the offspring are purple rather than red or white.

Question 13

Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. Also, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. What phenotypes would be expected from a cross between a true-breeding sharp-spined cactus and a spineless cactus?

Accepted Answer

The true-breeding sharp-spined cactus would have the genotype SSNN (since it is true-breeding for sharp spines and has spines), and the spineless cactus would have the genotype ssnn (since it lacks spines due to the nn genotype, the S gene's effect is irrelevant). Crossing these would result in all offspring being SsNn, which have sharp spines because they have at least one dominant allele for sharpness (S) and at least one dominant allele for having spines (N).

Question 14

A radish is a root vegetable that produces flowers that may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant trait. If true-breeding red-flowered, long radishes long radishes are crossed with true-breeding white oval radishes, the F1 will be expected to exhibit which of the following phenotypes?

Accepted Answer

In this scenario, flower color exhibits incomplete dominance, where the heterozygous condition results in a blend of the two parental phenotypes (red and white produce purple offspring). For the shape of the radish, long is dominant over oval. Therefore, crossing true-breeding red-flowered, long radishes with true-breeding white, oval radishes would result in F1 offspring that are all purple-flowered and long, as they inherit one allele for each trait from each parent.

Question 15

Which of the following relationships among alleles of a single gene best explains the observation that a single change in the gene encoding α-keratin results in chickens with frizzled feathers, increased food consumption, higher heart rate and delayed sexual maturity?

Accepted Answer

Pleiotropy occurs when one gene influences multiple phenotypic traits, which explains the diverse effects (frizzled feathers, increased food consumption, higher heart rate, delayed sexual maturity) from a single gene mutation in α-keratin.

Question 16

A gene for the MN blood group has codominant alleles M and N. If both children in a family are of blood type M, which of the following situations is possible?

Accepted Answer

If both children are of blood type M, it means they have either MM or MN genotypes. For this to happen, each parent must have at least one M allele to pass on to the children. Therefore, each parent could be either M (homozygous MM) or MN (heterozygous), making option A correct.

Question 17

Phenylketonuria (PKU) is a recessive human disorder in which an individual cannot appropriately break down the amino acid phenylalanine. This amino acid is not naturally produced by humans. Which of the following treatments would be most effective for people with PKU?

Accepted Answer

Regulating the individual's diet to severely limit the uptake of phenylalanine is the most effective treatment for PKU, as it directly addresses the inability to metabolize this amino acid properly.

Question 18

In human blood types, Rh positive is a trait that shows simple dominance over Rh negative. The Rh phenotype is recorded by stating "positive" or "negative" after the individuals ABO blood type. A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Which of the following phenotypes is possible for the father?

Accepted Answer

The woman has blood type A positive and can provide either an A or O allele and a positive Rh factor. The daughter is O positive, indicating she received an O allele and a positive Rh factor from her parents. The son is B negative, indicating he received a B allele and a negative Rh factor. For the children to have O and B blood types, the father must provide the O allele to the daughter and the B allele to the son, as well as the positive Rh factor to the daughter and a negative Rh factor to the son. Therefore, the father must have the genotype to provide a B allele and both Rh+ and Rh- alleles, making B positive (C) the only possible phenotype.

Question 19

Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. A second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. Which of the following explain why a crossing a true breeding spineless cactus with a dull-spined cactus could result in both sharp- and dull-spined offspring?

Accepted Answer

The spineless cactus must carry at least one dominant allele for gene S (for spine sharpness) but is homozygous recessive for gene N (which determines the presence of spines). When crossed with a dull-spined cactus (homozygous recessive at the S locus), the offspring can inherit the dominant S allele from the spineless parent and the recessive n allele from both parents, resulting in cacti with spines (due to the S allele) that can be either sharp or dull depending on the combination of alleles they inherit at the S locus.

Question 20

One of two major forms of neurofibromatosis results from inheriting a dominant allele of a gene with affected individuals having phenotypes that range from mild to very severe. Which of the following is the best explanation for why a young child is the first in her family to be diagnosed with a severe form of the condition?

Accepted Answer

Neurofibromatosis exhibits variable expressivity, meaning the severity of the condition can vary widely among individuals carrying the dominant allele. If one parent has a mild expression of the gene, they can pass it on to their child, who might then exhibit a more severe form of the condition.

Quiz 14: Mendelian Genetics