Question 1

Jermaine and Shikia are healthy parents of three young children.The oldest two,Bethany and Amber,are healthy,and they are six and four,respectively.Their youngest child was born with Peeling Skin Syndrome two years ago.Roscoe's skin constantly peels,and is red and itchy.If Jermaine and Shikia have another child,the probability that he or she will inherit the skin condition is

Accepted Answer

Peeling Skin Syndrome is a rare genetic disorder caused by mutations in the genes responsible for the structure and maintenance of the skin. Since their youngest child has the condition, we know that both Jermaine and Shikia carry at least one copy of the mutated gene. 
When two carriers of a rare genetic condition have children, there is a 25% chance for each child to inherit two copies of the mutated gene and therefore have the condition, a 50% chance to inherit one mutated gene and be a carrier like their parents, and a 25% chance to inherit two normal copies of the gene and not be affected. 
So the probability that their next child will inherit Peeling Skin Syndrome is 1/4 or 25%.

Question 2

The genotypic ratio expected from a dihybrid cross involving complete dominance is

Accepted Answer

In a dihybrid cross with complete dominance, the genotypic ratio is 9:3:3:1, representing the combinations of two traits with two alleles each.

Question 3

The second generation resulting from a genetic cross is the _______ generation.

Accepted Answer

The second generation resulting from a genetic cross is called F2 (filial 2) generation. In this question, the options include various combinations of letters and numbers. However, the convention used in genetics is to denote generations with letters (such as F for filial) followed by a number indicating the order of that particular generation. For example, F1 indicates the first filial generation and F2 indicates the second filial generation. The only option that follows this convention and includes the correct letter and number combination is D) F₂, which denotes the second filial generation resulting from a cross between a female (F) and a male (S) parent, where the parents have different alleles at two different genetic loci (B1 and B0).

Question 4

Eric and Janelle are carriers of the recessive allele causing Tay-Sachs disease,which is lethal in early childhood.If they have a healthy child,what is the probability that this child would NOT be a carrier of Tay-Sachs disease?

Accepted Answer

If Eric and Janelle are both carriers, their genotypes are Tt. The possible genotypes for their child are TT (not a carrier), Tt (carrier), and tt (affected). If the child is healthy, they cannot be tt, leaving TT and Tt as possibilities. The probability of being TT (not a carrier) is 1/3.

Question 5

Hillary is 8 years old and has neuronal ceroid lipofuscinosis,also known as Batten disease.It is autosomal recessive.She was fine until age five,when she began to lose her vision and stumble.She had learning difficulties in school and was diagnosed at age six.Hillary may only live into her twenties,experiencing dementia and seizures.Her younger brother Jaden,age six,is healthy,as are her parents.The probability that Jaden is a heterozygote is

Accepted Answer

Since Batten disease is autosomal recessive, both parents must be carriers (heterozygotes) for Hillary to be affected. Jaden, being healthy, could either be a carrier or not. The probability of him being a carrier (heterozygote) is 2/3, given that he is not affected.

Question 6

In a human pedigree that traces the inheritance of sickle cell disease,a half-filled circle represents a

Accepted Answer

In a pedigree, a half-filled circle represents a heterozygous female, indicating she is a carrier of the trait but does not express the disease.

Question 7

Sickle cell disease is inherited as an autosomal recessive trait.The genotype of an individual with sickle cell disease is

Accepted Answer

Sickle cell disease is caused by a mutation in the beta-globin gene (HBB) that results in the production of abnormal hemoglobin (HbS). The HBB gene is located on chromosome 11 and individuals inherit two copies (alleles) of this gene, one from each parent. Since sickle cell disease is an autosomal recessive disorder, an individual with the disease must have two recessive alleles (ss), one from each parent. Therefore, the genotype of an individual with sickle cell disease is homozygous recessive.

Question 8

The original pedigrees,used in France in the fifteenth century,resembled

Accepted Answer

The original pedigrees used in France in the fifteenth century resembled a bird's foot. This is because they were drawn with a single line that branched out into multiple lines, resembling the structure of a bird's foot.

Question 9

Which of the following genotypes is homozygous?

Accepted Answer

Homozygous means having two of the same allele for a particular gene. In this case, "RRYY" has two dominant alleles (R) and two dominant alleles (Y), making it homozygous dominant. The other options have a mixture of dominant and recessive alleles and are therefore heterozygous.

Question 10

In a human pedigree that traces the inheritance of albinism,a filled square represents a

Accepted Answer

In a pedigree chart, a filled square typically represents a male who expresses the trait being studied, in this case, albinism.

Question 11

A very narrow pedigree,such as that for Egypt's Ptolemy dynasty,reflects

Accepted Answer

A narrow pedigree reflects a limited number of individuals in a family tree, which can be a result of inbreeding (marriage between blood relatives). The Ptolemy dynasty of ancient Egypt is known for its high level of inbreeding, with marriages between siblings and cousins being common. This led to a very narrow pedigree with a limited number of ancestors, but also increased the risk of genetic disorders and health problems in offspring.

Question 12

A severe disease that is inherited as an autosomal recessive trait is more likely to skip generations in a pedigree than an autosomal recessive trait that causes a harmless phenotypic variant because

Accepted Answer

A severe autosomal recessive disease often has a negative impact on the health of those affected, making it less likely for them to reproduce. On the other hand, a harmless variant is unlikely to affect reproductive abilities. Hence, the disease is more likely to skip generations.

Question 13

One reason that dominant diseases remain in populations is that

Accepted Answer

Dominant diseases often do not produce symptoms until a person has already had children and passed on the disease-causing gene to their offspring. This makes it difficult to eradicate the disease from the population, as carriers may not be aware they have the disease until after they have passed it on to their children.

Question 14

In the Foofnagle family,the trait of being able to yodel affects members of both sexes in every generation.This trait could be

Accepted Answer

The trait is expressed in both sexes in every generation, which is consistent with autosomal dominant inheritance.

Question 15

Jaden is six years old.His sister Hillary has the autosomal recessive condition neuronal ceroid lipofuscinosis that affects learning and coordination.Their parents are healthy.The probability that Jaden is a homozygote for the wild type allele of the gene that causes the condition is

Accepted Answer

The answer of Jaden is six years old.His sister Hillary...

Question 16

For two traits A and B with two alleles each,the genotypes of the gametes that a heterozygote would produce are

Accepted Answer

A heterozygote for two traits A and B with two alleles each would produce gametes with the following genotypes: AB, Ab, aB, ab.

Question 17

Using the product rule,the probability that parents heterozygous for two traits (AaBb)produce an offspring homozygous recessive for the same two traits (aabb)is

Accepted Answer

The probability of producing an offspring homozygous recessive for one trait (aa) from heterozygous parents (Aa) is 1/4. Similarly, the probability for the second trait (bb) is also 1/4. Using the product rule, multiply these probabilities: 1/4 * 1/4 = 1/16.

Question 18

Ian and Bryony are both carriers for two autosomal recessive disorders,PKU (chromosome 12)and cystic fibrosis (chromosome 7).They are expecting a daughter.What is the probability that she will have PKU but not CF?

Accepted Answer

The probability of the daughter inheriting PKU is 1/4 (since both parents are carriers), and the probability of not inheriting CF is 3/4. The combined probability is 1/4 * 3/4 = 3/16.

Question 19

In a family that starts with you,your grandchildren would be the _______ generation.

Accepted Answer

In genetics, "F" stands for "filial," which refers to generations following the parental generation (P). The first generation of offspring is F1, and their offspring (your grandchildren) would be the F2 generation.

Question 20

Destiny has distal symphalangism - her fingers and toes are stiff,with tiny nails.She looks it up and finds it is an autosomal dominant trait.Since her parents do not have it,she reasons that she is a new mutation.However,if she has children,each of them,assuming her partner does not have the condition,has a(n)___ probability of inheriting the condition.

Accepted Answer

Since distal symphalangism is an autosomal dominant trait, each child of an affected individual has a 50% (1/2) chance of inheriting the condition if the other parent does not have it.

Quiz 4: Single-Gene Inheritance