Biology Unit 5 Exam

Mice genes

2.2

Scientists have found that DNA methylation suppresses crossing-over in the fungus Ascobolus immersus. Which of the following questions is most appropriately raised by this specific observation?

Is the level of genetic variation in the gametes related to the amount of DNADNA methylation observed?

Three ways meiosis generates genetic diversity?

Random fertilization allows random combination of genetic information, which helps synthesize genetically unique gametes. The fusion of a unique sperm together with a unique egg can introduce further variation. Crossing over, or recombination, is the exchange of chromosome segments between nonsister chromatids in meiosis. Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity. Random assortment of chromosomes produces many variations among daughter cells, giving rise to genetic diversity in offspring

Chi squared

The calculated chi square value is 9.24 and critical value is 7.82. The null hypothesis of independent assortment can be rejected.

If the woman and a man with normal clotting function have one biological daughter and one biological son, which children are predicted to have hemophilia a?

only the son

Pigeons demonstrate ZW sex determination, such that a ZZ genotype produces a male and a ZW genotype produces a female. The gene for feather color is located on the Z chromosome, and the red allele is dominant over the brown allele. Three crosses between brown male pigeons and red female pigeons were performed, and the results are shown below.

11

An African violet grower observes that genetically identical African violet plants growing near the walls of the greenhouse have white flowers, that plants growing farther away from the walls have pale blue flowers, and that plants growing nearest the center of the greenhouse have dark blue flowers. Which of the following best explains the differences in flower color of the African violets in the greenhouse?

An enzyme responsible for flower color does not fold correctly in cooler temperatures, and the greenhouse is warmest in the center.

Trisomy 21 is a condition in which a child is born with an extra chromosome in pair 21. Researchers assessed the frequency of children born with trisomy 21 by age of the mothers at birth (maternal age) and primary cause of the error leading to trisomy 21. The findings are presented in Figure 1. Based on the data in Figure 1, which of the following is most likely the primary cause of the pattern of frequency of trisomy 21 births in the selected maternal age-groups?

At older maternal ages, the incidence of errors in meiosis during egg production increases, which leads to an increase in nondisjunction.

Table 1 shows the stage and number of cells and chromosomes per cell at the end of the stage in a 2n=24 organism. Which of the following statements correctly describes the chromosomes in each daughter cell at the end of meiosis I?

Each daughter cell contains 12 chromosomes, each composed of two chromatids. Each chromosome is one of a pair of homologous chromosomes from the parent cell, with the other homologue found in the other daughter cell.

Which of the following questions about genetic diversity could most appropriately be answered by analysis of the model in Figure 1?

How does the independent assortment of the two sets of homologous chromosomes increase genetic diversity?

Australian dragon lizards have a ZW sex-determination system. The male genotype is homogametic (ZZ), and the female genotype is heterogametic (ZW). However, all eggs incubated at temperatures above 32°C tend to develop into females.Which of the following best explains how the development of phenotypic female Australian dragon lizards with a ZZ genotype occurs when incubation temperatures are above 32°C?

Incubation temperatures above 32°C32°C inhibit the genes on the ZZ chromosome that produce proteins necessary for male development.

During prophase I replicated homologous chromosomes pair up and undergo synapsis. What testable question is generated regarding synapsis and genetic variability by Figure 1 ?

Is the distance between two gene loci related to crossover rate?

Figure 1 illustrates the X and Y chromosomes during meiosis I and meiosis II of normal spermatogenesis in a mammal species. If the normal spermatogenesis is disrupted, the gametes can have different chromosomes than expected. Which of the following is the most likely cause of one of the four gametes having two X chromosomes and one having neither an X nor a Y chromosome?

Nondisjunction of the XX chromosome during meiosis II

When a mustard plant seedling is transferred to an environment with higher levels of carbon dioxide, the new leaves have a lower stomata-to-surface-area ratio than do the seedling's original leaves. Which of the following best explains how the leaves from the same plant can have different stomatal densities when exposed to an elevated carbon dioxide level? A. Increased photosynthesis leads to larger leaves that need more stomata for photosynthesis, leading to an increase in stomatal density. B. Leaf growth is promoted through increased photosynthesis, but the genetically regulated rate of stomatal production is not altered, leading to a decrease in stomatal density. C. Leaf growth is inhibited by decreased photosynthesis, and the genetically regulated rate of stomatal production remains the same, leading to an increase in stomatal density. D. Leaf growth is inhibited by decreased photosynthesis, and the genetically regulated rate of stomatal production remains the same, leading to a decrease in stomatal density.

Leaf growth is promoted through increased photosynthesis but the genetically regulated rate of stomatal production is not altered leading to a decrease in stomatal density.

Meiosis begins with one diploid parent cell. Which of the following best explains how meiosis results in four haploid daughter cells?

Meiosis involves two rounds of division and double chromosomes remain in pairs during metaphase 1.

Which of the following represents the most accurate prediction of the cause of the inheritance pattern illustrated in the karyotype?

The chromosomes failed to separate during gamete formation

Saccharomyces cerevisiae is a diploid yeast species that can reproduce either sexually or asexually. An experiment was performed to induce mitotically dividing S. cerevisiae cells in G2 to undergo meiosis. Which of the following best describes the steps these cells will follow to form gametes?

The first division will reduce the number of chromosomes by half for each daughter cell, and the second division will result in each daughter cell having one-fourth of the original number of chromosomes.

Red-green color blindness in humans is caused by a recessive allele located on the X chromosome. Figure 1 shows the potential offspring of a female who is red-green color-blind and a male with full-color vision. All of the possible male offspring would be color-blind, and all of the possible female offspring would have full-color vision. If during the production of male gametes an error in meiosis occurred, sperm containing both an X and a Y chromosome could be produced. How would the extra chromosome affect the male offspring produced by the gamete?

The male offspring would have full-color vision, because of the presence of the extra XX chromosome.

In fruit flies, sepia eyes and ebony body are traits that display autosomal recessive patterns of inheritance. To investigate whether the traits are genetically linked, students cross wild-type flies with a line of flies that have sepia eyes and ebony bodies. The students observe that all the flies in the F1 generation have normal eyes and normal bodies. The students allow the flies in the F1 generation to mate and produce an F2 generation. The students then record observations for the flies in the F2 generation and use the data to perform a chi-square goodness-of-fit test for a model of independent assortment. The setup for the chi-square goodness-of-fit test is presented in Table 1.

The null hypothesis can be rejected, and the students should conclude that the data may have resulted from genetic linkage.

A gene that influences coat color in domestic cats is located on the X chromosome. A female cat that is heterozygous for the gene (XBXO) has a calico-colored coat. In a genetics experiment, researchers mate a calico-colored female cat (XBXO) with an orange-colored male cat (XOY) to produce an F1 generation. The researchers record observations for the cats in the F1 generation and plan to use the data to perform a chi-square goodness-of-fit test for a model of X-linked inheritance. The data for the chi-square goodness-of-fit test are presented in Table 1.

The null hypothesis cannot be rejected because the chi-square value is less than the critical value.

In order to determine the effects of age on the accumulation of mitochondrial mutations, mitochondrial DNA samples from young mice (3 months) and old mice (30 months) were observed for mutations.

There is an increase in the mean number of mutations for the two age groups of 9.2 mutations per 106106 base pairs. This is more critical in female mammals since mitochondria are maternally inherited.

A scientist studying phenotypic variation in a species of butterfly observed that genetically identical caterpillars grown in similar cages but exposed to different colored lights developed into butterflies with differences in wing color and body size, as shown in Table 1.Which of the following best explains the cause of the phenotypic variation observed in the butterflies?

There was differential gene expression of wing color and body size in response to the colors of light the caterpillars were exposed to.

An experiment was performed to determine the mode of inheritance of two mouse genes, one for fur color and one for fur length. It is known that black fur (B) is dominant over white fur (b) and that long fur (L) is dominant over short fur (l). To determine how the genes are inherited, a cross was performed between two true-breeding mice, one with long black fur and one with short white fur. Their progeny, the F1 generation, all had long black fur. Five F1 male-female pairs were then crossed with one another. The F2 generation phenotypes for each cross are shown in Table·1.

2.2

Both mitosis and meiosis begin with a parent cell that is diploid. Which of the following best describes how mitosis and meiosis result in daughter cells with different numbers of chromosomes?

Mitosis produces two identical diploid daughter cells after one round of division. Meiosis produces four haploid daughter cells after two rounds of division.

A research team has genetically engineered a strain of fruit flies to eliminate errors during DNA replication. The team claims that this will eliminate genetic variation in the engineered flies. A second research team claims that eliminating errors during DNA replication will not entirely eliminate genetic variation in the engineered flies. Provide ONE piece of evidence that would indicate new genetic variation has occurred in the engineered flies.

New phenotypes • Different DNA sequence • New genotypes • Chromosomal differences • Different mRNA sequence • Protein with different amino acid sequence

Insulin is a hormone produced by some pancreatic cells. Scientists have isolated the DNA sequence that codes for human insulin production. Which of the following best predicts the effect of inserting this gene into the DNA of a bacterial cell?

The recombinant bacterium will produce human insulin using its own machinery.

Describe ONE mechanism that could lead to genetic variation in the engineered strain of flies.

• Sexual reproduction produces offspring with new combinations of alleles/traits • Meiosis produces new combinations of alleles/traits • Crossing over produces new combinations of alleles/traits • Independent assortment produces new combinations of alleles/traits • Random fertilization produces new combinations of alleles/traits • Immigration/gene flow introduces new alleles/gene sequences • Viral infection inserts DNA into genome • Nondisjunction causes anomaly in chromosome number • Chromosomal rearrangements (e.g., large deletions, duplications, translocations, inversions, transposons, etc.) inactivate genes or result in multiple copies of genes • Radiation or chemicals or mutagens induce mutations/changes in DNA