Chapter 15-17 In-class Questions

What phenotypic ratio results from epistasis of the type in row M?

12:3:1

Analysis of mitochondrial DNA can answer interesting and important questions. For which of the following questions would analyzing mitochondrial DNA be futile?

Are you my father?

Direct-to-consumer genetic tests: Select all that apply.

can be purchased directly by consumers. may or may not be reliable.

A trait due to a gene in the Y chromosome can be observed in:

males.

The incidence of Down syndrome is positively correlated with:

the mother's age.

The pedigree shown here pertains to a trait due to a rare, X-linked recessive mutation. Individual 1 has no family history of the trait and individual 2 is affected, but the genotypes and phenotypes of individuals 1, 3, and 4 are unknown. What is the (approximate) probability that individual 1 is heterozygous? What is the probability that individual 3 is affected? What is the (approximate) probability that individual 4 is affected?

0; 0; 0

In genetics, the dash symbol (-) is a "wild card" that stands for either the dominant allele or the recessive allele; for example, A- means the individual has either the genotype AA or Aa. Two genes that undergo independent assortment affect fruit color in summer squash. Each gene has two alleles, one of which is dominant for fruit color. Genotypes of the form A- B- and A- bb have white fruit, genotypes of the form aa B- have yellow fruit, and genotype aa bb has green fruit. What ratio of white:yellow : green is expected from the cross Aa Bb Aa Bb?

12:3:1

The phenotype ratio of the progeny of a cross between two individuals with a trait that displays incomplete dominance is:

1:2:1.

In the diagram below, the horizontal lines represent DNA strands in a double-stranded molecule, the vertical lines mark the positions of cleavage sites for a particular restriction enzyme, the arrows show the positions of primers used in the polymerase chain reaction (PCR) to amplify the region, and the numbers are the number of nucleotides between successive restriction sites. If this particular DNA molecule is amplified and then cleaved with the restriction enzymes, what size band(s) would be observed in a gel?

3 kb and 2 kb

In humans, ability to roll the tongue (R) is dominant to being unable to roll (r). Having freckles (F) is dominant to having no freckles (f). A man heterozygous for both traits marries a woman heterozygous for both traits. What is the probability that they will have a child with freckles?

3/4

If there are 3 different alleles for a particular gene in a population of diploid organisms, how many different genotypes are possible in the population?

6

Four genes (A, B, C, and D) are in the same chromosome in the sequence D, A, B, and C. The distance between A and B is 4 map units, between A and C is 6 map units, and between B and D is 5 map units. The recombination frequency between genes C and D should be:

7%.

In pea plants, flowers are either white or purple; the purple color is produced by pigments called anthocyanins. The production of anthocyanins is a two-step process: the first is controlled by the C gene and the second by the P gene. Both genes must produce functional proteins for anthocyanin to be expressed. For each gene, the dominant (C and P) alleles produce functional proteins. You cross two pea plants, each with the genotype CcPp. What proportion of their offspring will have white flowers?

7/16

Two genes that are 8.2 map units apart will have a recombination frequency of:

8.2%.

What phenotypic ratio results from epistasis of the type in row L?

9:3:4

In genetics, the dash symbol (-) is a "wild card" that stands for either the dominant allele or the recessive allele; for example, A- means the individual has either the genotype AA or Aa. Two genes that undergo independent assortment affect coat color in Duroc pigs. Each gene has two alleles, one of which is dominant for coat color. Genotypes of the form A- B- are red, those of the form A- bb and aa B- are sandy, and genotype aa bb is white. What ratio of red:sandy:white is expected from the cross Aa Bb Aa Bb?

9:6:1

Cancer can be caused by mutations. Genetic analysis of a tumor found in a patient we shall call Anna shows that the cell proliferation was triggered by a somatic mutation in the MYC gene, causing this gene to be inappropriately activated. Anna is concerned about passing this cancer on to the children she plans to have in the future. Should she be concerned?

No, she should not worry about her children because this did not occur in a germ-line cell.

The most common form of hemophilia is a defect in blood clotting factor VIII, which is caused by a mutant form of a gene in the X chromosome. A girl is born with hemophilia. Both parents have normal phenotypes. Which of the following might explain this girl's hemophilia?

Nondisjunction during sperm formation resulted in her receiving no sex chromosome from her father and an X chromosome from her mother; she is XO.

Identical twins have the same: Select all that apply.

genotype. karyotype. DNA type.

A normal woman with a color-blind brother:

has a 50% chance of being heterozygous for the gene causing color blindness.

Genes a and b are located close together in the same chromosome. Allele A for long wings is completely dominant to allele a for short wings. Allele B for light body color is completely dominant to allele b for dark body color. A female fly is heterozygous for both genes such that alleles A and b are present in one homolog, whereas alleles a and B are present in the other homolog. If she is crossed with a male fly that is homozygous recessive for both genes, then the majority of their progeny would:

have short wings and a light body or long wings and a dark body.

An individual is homozygous for a gene if:

they developed from a sperm and an egg that carried the same allele.

Genes that fail to show independent assortment are said to be linked.

true

The F1 generation of a cross between two individuals, one that is homozygous dominant for a trait and the other that is homozygous recessive for the trait, will yield progeny with the same phenotype.

true

The genotype of a fetus can be screened for SNPs associated with some diseases.

true.

What is the probability that an individual is Aa or AA if his or her parents are both heterozygous for the trait?

¾

Segregation of alleles corresponds to the separation of:

chromosomes.

What kind of genetic variation can alter gene dosage?

copy-number variations

What process allows a gamete to carry a chromosome containing some genes with an allele from the paternal chromosome and other genes with an allele from the maternal chromosome?

crossing over

Harmful mutations are often eliminated in a population because they:

decrease survival and/or reproduction of the individuals.

Failure of cell division in anaphase in meiosis can result in a:

diploid gamete. triploid fertilized egg.

Autosomal trisomies are associated with the X or Y chromosome.

false

For unlinked genes, the sorting of one gene pair influences the sorting of another gene pair.

false

Harmful mutations are always eliminated from the genome in one or a few generations, because they decrease the survival and reproduction rates of the individuals that carry them.

false

It is impossible to override a genetic predisposition to a disease such as skin cancer.

false

The total number of chromosomes differs between human males and females.

false

A recessive X-linked trait can be found in: Select all that apply.

females. males.

With regard to alleles that encode different forms of beta-hemoglobin in humans and their relation to malaria, which of the following are examples of phenotypes? Select all that apply.

sickle-cell anemia susceptibility to malaria sickled red blood cells

The frequency of recombination is ______________ for genes that are closer together compared to genes that are further apart in the same chromosome.

smaller

When the DNA sequence of the gene that codes for the peptide hormone insulin is compared in two mammals (e.g., humans and rats), most of the sequence differences are synonymous mutations. These far outnumber sequence differences that result in amino acid substitutions. Why might this be?

Amino acid substitutions often result in proteins that have lost or compromised function and, therefore, are selected against.

A restriction-fragment length polymorphism at a site in the X chromosome has three alleles, A1, A2, and A3. The gel below is the DNA fingerprint for two girls who have the same parents. What is the genotype of the mother? Of the father?

A2/A3; A2

Which of the following situations would have caused Mendel to observe patterns of inheritance that supported the model of blending inheritance instead of transmission of alleles causing discrete differences?

All of these choices are correct.

Three genes (A, B, and C) are in the same chromosome. The distance between A and B is 1 map unit, between B and C is 4 map units and between A and C is 3 map units. The correct order of genes in the chromosome is:

B A C.

The frequency of recombination during meiosis is a function of:

the distance between genes: the farther apart the genes are, the more frequent the recombination between them.

A restriction-fragment length polymorphism at a site in the X chromosome has three alleles, A1, A2, and A3. The gel below is the DNA fingerprint for two prospective parents (Mo and Fa) along with DNA types that might (or might not) correspond to their offspring. What are the possible phenotypes of daughters from this mating?

H and L

Red-green color blindness is a sex-linked recessive trait in humans. If a carrier female (heterozygous for the trait) mated with an affected male, what would be the expected outcome(s)?

Half of the daughters would be color blind.

_______________ results in a given genotype not necessarily producing the same phenotype. Select all that apply.

Incomplete penetrance Variable expressivity

A restriction-fragment length polymorphism at a site in the X chromosome has three alleles, A1, A2, and A3. The gel below is the DNA fingerprint for two prospective parents (Mo and Fa) as well as DNA types that may (or may not) correspond to their possible offspring. What are the possible phenotypes of sons from this mating?

K and Q

Which statements about mutations are false? Select all that apply.

Mutations are usually caused by exposure to radiation. Mutations occur as a direct response to an organism's attempt to change one of its traits.

Which of the following is(are) a benefit of genetic testing? Select all that apply.

Newborns can be screened for treatable diseases. Individuals can find out whether or not they carry harmful recessive alleles. Adults can find out whether or not they have specific risk factors for some diseases.

Many SNPs are regarded as "neutral" in the sense of having little or no effect on the likelihood of survival or reproduction of the different genotypes. Could you ever say for certain that a particular SNP is "neutral"? Select all that apply.

No, because any effect may be too small to detect. No, because you can never prove a negative.

The nonmutant allele of the BRCA1 gene helps to suppress tumor formation in women who are heterozygous for the mutation. Women homozygous for BRCA1 nevertheless have a 50% to 70% chance of developing breast cancer before age 70, and the usual reason is that the nonmutant allele is lost or inactivated in a lineage of cells. One possible mechanism for such "loss of heterozygosity" is:

a somatic mutation in a breast cell inactivates the nonmutant BRCA1 allele.

A Y-chromosome haplotype is a set of Y-linked nucleotides that:

allow one Y chromosome to be distinguished from another.

The human X chromosome carries approximately 1000 genes. The Y chromosome contains only about 50 genes. How can males survive with only these 50 genes in the Y chromosome?

The Y is paired with a functional X chromosome, which has all the genes.

Because of its unique structure, mutations in the Y chromosome:

are accumulated within individual Y chromosome lineages.

The gene density of the X chromosome is best described by which of the following statements?

The gene density of the X chromosome is like that of the gene density in an autosome.

In Drosophila, the red-eye allele for eye color exhibits complete dominance over the recessive white-eye allele. In some of Thomas Hunt Morgan's initial experiments, he crossed red-eyed female flies with white-eyed males. When he then crossed the F1 red-eyed heterozygous females with red-eyed males, Morgan found that half of the male progeny were white-eyed. What is the most likely explanation of this result?

The gene responsible for eye color is on the X chromosome.

Imagine two different pea plant strains: one of which has a trait that is produced by the interaction of many genes, and the other of which has a trait that is produced by a single gene with two alleles and incomplete dominance. If each of these pea plant strains self-fertilizes, how would the progeny of each cross differ?

The progeny from the cross of the plant with the single gene trait would have three phenotypes, whereas the progeny of the cross of the plant with the trait caused by many genes would have a more complex array of phenotypes.

Which of the following statements is true of human sex chromosomes?

There are sex-linked genes that males have that females do not have.

In England, a man who is upset about the amount of dog feces on his lawn supposedly collected hair samples from neighborhood dogs and compared their DNA types with that of the feces, thereby identifying the offending dog (and the negligent owner). It this possible?

This is not only possible, but it is fairly easy.

The fact that the ratio of human male to female births is nearly 1:1 demonstrates that:

X and Y chromosomes demonstrate segregation.

Nondisjunction of X chromosomes that occurs in the first meiotic division results in eggs with the following genotypes: Select all that apply.

XX. O.

Which of the following are useful in reconstructing phylogenetic histories? Select all that apply.

Y chromosome mitochondrial DNA chloroplast DNA

An XXY person inherited three sex chromosomes due to erroneous meiosis in the person's parents. The syndrome associated with this particular aneuploidy is called Klinefelter Syndrome. This person can be: Select all that apply.

a male who received an X normally from his mom but an X and Y from his dad due to nondisjunction. a male who received two X's from his mom due to nondisjunction but a Y normally from his dad.

Ultraviolet light can penetrate the skin and damage DNA, and it can also destroy the B vitamin folate needed for bone-marrow maturation and the development of red blood cells. On the other hand, exposure to ultraviolet light is beneficial in the synthesis of vitamin D3, which is important for growth, calcium absorption, and bone development. The amount of ultraviolet light that penetrates the skin depends on the skin's pigmentation: more melanin (skin pigment) means less penetration. Which of the following do you think would best describe the pressure of natural selection on human skin pigmentation?

a pressure for darker or lighter skin, depending on the intensity of UV in a geographical region

The mitochondrial DNA sequence of a woman should match all of the following people except:

her father.

If a population has only one allelic form of the gene, every individual is:

homozygous.

In humans, mitochondria (and their genomes) show:

maternal inheritance.

Nondisjunction in ______________ results in offspring inheriting the mutation.

meiosis

In animals with sex chromosomes, males inherit their X chromosome from their ___ and transmit it to their ___.

mothers; daughters

The Y chromosome can be used to trace ancestry because:

mutations in the Y chromosome occurred as people migrated around the globe.

Most genetic variation in a population is:

neutral.

Y-linked traits are:

never inherited or transmitted by females, and are transmitted by affected fathers only to their sons.

You perform PCR to amplify DNA from a specific small region of a person's genome to detect whether the individual's DNA contains a small deletion in a gene. You separate the PCR products on a gel. The bands in the gel constitute a:

phenotype.

The genetic map shown here depicts the locations of five single-nucleotide polymorphisms (SNPs, designated a-e) in an autosome and the frequency of recombination (in percent) between adjacent SNPs. The region includes a genetic risk factor Q for a disease, which may be located in position M, H, K, or L. Pedigree studies indicate that the frequencies of recombination between each of the SNPs and Q are as follows: percent recombination a-Q equals 20%. percent recombination b-Q equals 16%. percent recombination c-Q equals 4%. percent recombination d-Q equals 4%. percent recombination e-Q equals 20%. What is the most likely position of Q in the genetic map?

position K

Beneficial mutations can: Select all that apply.

protect from disease. be repaired. permit an organism to become adapted to its environment.

Mendel's principle of independent assortment corresponds to which part of meiosis?

random alignment of homologs on the metaphase plate during metaphase I

Mendel's principle of segregation corresponds to what part of meiosis?

separation of homologs in anaphase I

If a woman's husband shows an undesirable Y-linked trait, then she:

should be concerned; her husband will definitely transmit it to their sons.