Genetics Exam 2 HW questions

Some multifactorial traits are determined by many interacting genes, each of which may have several alleles. If such a trait is measured in a population, what phenotypic pattern is expected?

The population will have continuous variation in phenotypic expression.

Exposure to UV light from the sun or tanning beds causes

Thymine dimers

Replacing an adenine nucleotide with a guanine is an example of a

Transition

Replacing a thymine nucleotide with a guanine is an example of a

Transversion

The addition of a single base pair to a gene's DNA sequence can cause a frameshift mutation.

True

Alkylating agents, such as ethylmethane sulfate (EMS), are mutagens because they

add ethyl or methyl groups to bases.

After a tautomeric shift in adenine,

adenine bonds with cytosine.

According to Mendel's Law of Independent Assortment,

alleles of genes on different chromosomes assort randomly into different gametes.

An alternative form of a single gene is known as

allle

Pea shape is controlled by a gene that specifies an enzyme known as Sbe1 (for Starch-branching enzyme 1). A recessive allele of Sbe1 likely encodes

an Sbe1 enzyme with reduced function.

UV light and other ionizing radiations damage DNA molecules by

creating thymine dimers between adjacent thymines in the DNA chain.

The alleles present in an individual make up the individual's

genotype

A rare recessive trait in a pedigree is indicated by which pattern of inheritance?

horizontal

In a tautomeric shift,

hydrogen atoms move to form a base with altered hydrogen properties.

What is the term for crosses between parents that differ in only one trait?

monohybrid

Assume that in guinea pigs, dark brown fur (B) is dominant to black fur (b). If you mate a black guinea pig with a homozygous brown guinea pig, what proportion of the progeny will be homozygous?

none

The first step in base excision repair is

recognizing and excising the incorrect base from a nucleotide.

Proofreading by DNA polymerase involves the removal of

several bases on the newly-synthesized strand of DNA

In light repair,

the covalent bonds between the thymine dimers are broken.

When DNA is damaged by UV light and is not repaired

the damaged part will be excised and allow DNA replication to proceed.

Whether an allele is completely dominant, incompletely dominant, or codominant to a second allele of the same gene depends on

the functions of the proteins determined by the two alleles

The diploid garden pea plant has 14 chromosomes. The haploid fungus Neurospora crassa has 7 chromosomes. Neither organism has separate male and female individuals. Therefore, the number of linkage groups in these two organisms is

the garden pea has 7 linkage groups, and Neurospora has 7.

The mutations found in the CF gene that result in cystic fibrosis are recessive because

the protein produced by the normal allele is sufficient for normal cellular function.

In the testcross Aa Bb × aa bb, what proportion of individuals are expected to be homozygous for both genes in the F1 generation?

¼

In some genetically engineered corn plants, a Bt gene was added to a chromosome. The Bt gene specifies a protein called Bt that is lethal to certain flying insect pests that eat the corn plants. If the corn plant is is heterozygous for the Bt gene (one homolog has the introduced Bt gene and the other does not), what proportion of the sperm would carry the Bt gene? Is the presence of the Bt gene (a mutation) dominant or recessive to its absence (the wild type)?

½ and dominant

A dihybrid testcross is made between genes H and I. Four categories of offspring are produced: H I, H i, h I, and h i. How many degrees of freedom would there be in a chi-square test for goodness of fit of the null hypothesis that the H and I genes are unlinked?

0

If a gene for a trait is monomorphic in a population and two random individuals mate, what would be the most likely phenotypic ratio for that trait in the offspring?

1

Genes A and B are on different (nonhomologous) chromosomes. If an individual's genotype is Aa Bb, what is the genotypic ratio of gametes produced?

1 A B : 1 A b : 1 a B : 1 a b

Assume that in guinea pigs, dark brown fur (B) is dominant to black fur (b). If you mate a homozygous black guinea pig with a heterozygous brown guinea pig, what proportion of the progeny will be black?

1/2

In a monohybrid cross AA × aa, what proportion of heterozygotes is expected among the F2 offspring?

1/2

In a monohybrid cross AA × aa, what proportion of homozygotes is expected among the F2 offspring?

1/2

If the parents of a family already have two boys, what is the probability that the next two offspring will both be girls?

1/4

In the dihybrid cross AA BB × aa bb, what proportion of heterozygotes for both gene pairs is expected among the F2 offspring?

1/4

In the dihybrid cross Aa Bb × aa bb, what proportion of heterozygotes for both gene pairs is expected among the F1 offspring?

1/4

Suppose that in plants, smooth seeds (S) is dominant to wrinkled seeds (s) and tall plants (T) is dominant to short plants (t). An F1 tall plant with smooth seeds was crossed to a parent plant that was short and wrinkled. What proportion of the progeny is expected to be heterozygous for tall and smooth?

1/4

Suppose that in plants, smooth seeds (S) is dominant to wrinkled seeds (s), and tall plants (T) is dominant to short plants (t). An F1 plant from a mating between homozygous plants that were tall/smooth and short/wrinkled was crossed to the short/wrinkled parent. What proportion of the progeny is homozygous for short and wrinkled alleles?

1/4

Calculate the probability of homozygous recessive offspring with from the cross Aa Bb cc dd Ee Ff × Aa Bb Cc dd Ee Ff.

1/512

Sickle cell anemia is a recessive trait in humans. In a cross between a father who has sickle cell anemia and a mother who is heterozygous for the sickle cell allele, what is the probability that all of their first three children will be unaffected?

1/8

If an individual has 10 gene pairs, how many different gametes can be formed if three of the gene pairs are homozygous and the remaining seven gene pairs are heterozygous?

128

If a trait is controlled by two codominant alleles of one gene, what phenotypic ratio is expected in the offspring of a mating of two heterozygotes?

1:2:1

Two alleles of gene C control hair color in horses: C¹ and C². Horses homozygous for allele C¹ are red, heterozygotes are yellow, and C² homozygotes are cream. In the offspring of matings between heterozygotes, what phenotypic ratio is expected?

1:2:1

Suppose the L and M genes are on the same chromosome but separated by 100 map units. What fraction of the progeny from the cross L M / l m × l m / l m would be L m / l m?

25%

The dominant Huntington disease allele causes severe neural/brain damage at approximately age 40. A female whose mother has Huntington disease marries a male whose parents are normal. It is not known if the female has the disease. Keeping in mind that the disease allele is rare in the population, what is the probability that their firstborn will inherit the gene that causes Huntington disease?

25%

Which genotypic ratio indicates a recessive lethal allele when two heterozygotes are mated?

2:1

DNA polymerases use their ________ activity to remove a mismatched base

3->5 exonuclease

A disease is caused by homozygosity for the g allele (G is the corresponding wild-type allele). However, the penetrance of the disease is 75%. Two individuals known to be heterozygotes have a child. What is the probability that the child exhibits the disease?

3/16

In a dihybrid cross AA bb × aa BB, what proportion of the F2 offspring is expected to be homozygous for at least one gene?

3/4

Which of the following probabilities is correct regarding a mating of an Ss RR individual to an individual who is Ss Rr ? (A - indicates the the second allele is either dominant or recessive.)

37.5

In Drosophila, the genes y (yellow body) and car (carnation eyes) are located at opposite ends of the X chromosome. In doubly heterozygous females (y+ car+ / y car), a single chiasma is observed somewhere along the X chromosome in 90% of the examined oocytes. No X chromosomes with multiple chiasmata are observed. What percentage of the male progeny from such a female would be recombinant for y and car?

40

In Drosophila, the genes y (yellow body) and car (carnation eyes) are located at opposite ends of the X chromosome. In doubly heterozygous females (y+ car+ / y car), a single chiasma is observed somewhere along the X chromosome in 90% of the examined oocytes. No X chromosomes with multiple chiasmata are observed. What percentage of the male progeny from such a female would be recombinant for y and car?

45%

Suppose the map for a particular human chromosome interval is: a——1 m.u.——b——1 m.u.——c——1 m.u.——d——1 m.u.——e——1 m.u.——f In a man heterozygous for all six genes, what fraction of his sperm would be recombinant in the a-f interval?

5%

Assume that the mutation rate for a given gene is 5 × 10−6 mutations per generation. For that gene, how many mutations would be expected if 10 million sperm are examined?

50

In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b——30 m.u.——c——20 m.u.——sp This region exhibits 90% interference. How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

6

A particular flower can be purple, blue, red, or white. A pure-breeding purple plant is crossed with a pure-breeding white plant and the F1 are then crossed to produce an F2 generation. Which phenotypic ratio in the F2 may indicate that flower color in these plants is controlled by two genes that interact additively?

9:3:3:1

Which ratio would indicate that a phenotype is controlled by multiple genes?

9:3:3:1

A particular flower can be blue, red, or white. A pure-breeding red plant is crossed with a pure-breeding white one, and the F1 are then crossed to produce an F2 generation. Which of the following phenotypic ratios in the F2 indicate that flower color in these plants is controlled by two genes?

9:3:4

Mendel's law of independent assortment dictates that an Aa Bb dihybrid would make equal numbers of four gamete types. What are these four gamete types?

A B; A b; a B; a b

According to Mendel's law of equal segregation, an Aa monohybrid makes two types of gametes with equal frequency. These two gamete types are:

A and a

Among the dihybrid crosses below, which will produce a 1:1 phenotypic ratio?

AaBB x aaBB

Among the dihybrid crosses below, which will produce offspring with a 1:1:1:1 genotypic ratio?

AaBb x aabb

An allele that expresses its phenotype even when heterozygous with a recessive allele is termed

Dominant

In some flowers, a purple pigment is synthesized from a red precursor pigment. In the absence of all pigment, flowers are white. A pure-breeding plant with red flowers was crossed to a pure-breeding plant with white flowers. All of the F1 plants had white flowers. The F1 plants were crossed to each other, and the F2 consisted of 166 plants: 123 with white flowers, 32 with purple flowers, and 11 with red flowers. How do these results suggest that flower color is determined?

Dominant allele masks the effects of the other gene

A curly-winged fruit fly mates with a pure-breeding fruit fly with normal (straight) wings. The F1 mate with each other to produce an F2 generation that consists of 160 flies with curled wings and 80 with straight wings. What can you infer from this observation?

Dominant curled allele is recessive and lethal

If a phenotype is controlled by the genotypes at two different loci, a possible interaction between alleles of these genes can be called

Epistasis

The first offspring from the parents are called

F1

In a frameshift mutation all of the amino acids before the shift are changed

False

In humans, the genes for red-green color blindness (R = normal, r = color blind) and hemophilia A (H = normal, h = hemophilia) are both X-linked and only 3 map units apart. Suppose a woman has four sons, and two are color blind but have normal blood clotting and two have hemophilia but normal color vision. What is the probable genotype of the woman?

H r / h R

Another name for a chromosome is a _______, because it contains alleles that are often inherited together.

Linkage group

Genes A and B are so close together on the same chromosome that crossing-over occurs between A and B in only 1 in a million meioses. An AA BB individual mates with an aa bb individual to produce an F1 that is A B / a b. If 100 progeny are observed, what genotypic ratio is expected in the gametes produced by the F1?

Only parental 1 A B : 1 a b

What is the consequence to a bacterial cell of a mutation that inactivates the enzyme responsible for methylating the A in the DNA sequence 5′ GATC?

Parental and new DNA strands cannot be distinguished during mismatch repair.

What can explain the phenomenon where the same genotype might give rise to different phenotypes?

Penetrance and expressivity

What does the pattern of inheritance in this pedigree indicate about the disease allele?

Recessive

What genetic phenomenon might a 2:1 phenotypic ratio indicate?

Recessive lethal

A particular flower can be purple, blue, red, or white. Two different pure-breeding white plants are crossed and the F1 are then crossed to produce an F2 generation. What might a 9:7 phenotypic ratio in the F2 indicate?

Reciprocal recessive epistasis

An Ss × Ss mating is performed. If the phenotypic ratio of the progeny is 3 S- (- indicates that the other allele is unknown) to 1 ss, then

S is dominant to the s

A bacterial mismatch repair system is able to correct replication errors that insert an incorrect nucleotide. How is this repair system able to determine which mismatched base is

Some bases of the parental strand are methylated, while none of the new strand are

The reason that the HD allele acts as a dominant allele is that

The HD mutation results in a protein that can damage nerve cells

A nucleotide deletion during DNA replication

causes the amino acids encoded after the deletion to be incorrect

ABO blood type demonstrates which of the following inheritance patterns?

codominance, complete

What structure is responsible for maintaining the connection between homologous chromosomes until anaphase of meiosis I?

cohesin complexes that are located distal to the crossover and hold sister chromatids together