bio retake

The diploid number of chromosomes in the cell of a domesticated dog is 78. Which of the following options includes the correct number of chromosomes in a cell after each cellular process (G2 checkpoint, meiosis, and fertilization, respectively)?

78, 39, 78

In pea plants, flower color and the length of the flower’s pollen grains are genetically determined. Researchers studying pea plants crossed homozygous dominant pea plants with homozygous recessive pea plants. The F1 plants were then crossed, and the number of offspring with each phenotype was recorded. The researchers’ observed data, however, differed from the expected data. The researchers did a chi-square analysis and calculated the chi-square value to be 5.5.

The differences between observed data and expected data are due to chance.

A male fruit fly (Drosophila melanogaster) with red eyes and long wings was mated with a female with purple eyes and vestigial wings. All of the offspring in the F₁ generation had red eyes and long wings. These F₁ flies were test crossed with purple-eyed, vestigial-winged flies. Their offspring, the F₂ generation, appeared as indicated below.

In the F₂ generation, the results are best explained by the fact that

these genes for eye color and wing shape are found on the same chromosome

R. C. Punnett conducted experiments on the inheritance of traits in the sweet pea, Lathyrus odoratus. In one experiment, he crossed two different true-breeding sweet pea plant strains, one with erect petals and long pollen, and the other with hooded petals and round pollen. All the offspring (F1 generation) had erect petals and long pollen (Figure 1).

Figure 1. Sweet pea plant cross

Next, Punnett allowed the F1 generation to self-fertilize and recorded the phenotypes of their offspring. The data are shown in Table 1.

 

Table 1. F2 results of F1 self-fertilization cross

Phenotype of	Number of Offspring
Erect petals, long pollen	765
Erect petals, round pollen	62
Hooded petals, long pollen	71
Hooded petals, round pollen	220
Total	1,118

Sweet pea plants have a diploid chromosome number of 14.

Which of the following best explains how the sweet pea plants in the parental generation produce offspring with 14 chromosomes?

Meiosis I and II lead to the formation of cells with 7 chromosomes. During meiosis I, homologous chromosomes separate. During meiosis II, sister chromatids separate. Two cells combine during fertilization to produce offspring with 14 chromosomes.

In anaphase I of meiosis, cohesion between the centromeres of sister chromatids is maintained while homologous chromosomes migrate to opposite poles of the cell along the meiotic spindle as represented in Figure 1.

Figure 1. Migration of homologous chromosomes during anaphase I of meiosis

A compound that prevents the separation of the homologous chromosomes in anaphase I is being studied. Which of the following questions can be best answered during this study?

Is there a pattern to the movement of homologous chromosomes in the presence of this compound?

The tadpoles of Mexican spadefoot toads are known to exhibit phenotypic plasticity depending on food availability. Tadpole mouthparts can vary significantly, prompting researchers to categorize them as either omnivore-morph or carnivore-morph. Carnivore-morph tadpoles are larger and have mouthparts that are better suited for predation. Remarkably, carnivore-morph tadpoles can change into omnivore-morph tadpoles when the food supply changes.

Which of the following best describes an advantage of the phenotypic plasticity displayed by the tadpoles?

C It gives the tadpoles increased versatility with respect to diet.

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?

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.

In humans, red-green color blindness is a sex-linked recessive trait. If a man and a woman produce a color-blind son, which of the following must be true?

The mother carries the allele for color blindness.

In garden peas, a single gene controls stem length. The recessive allele (t) produces short stems when homozygous. The dominant allele (T) produces long stems. A short-stemmed plant is crossed with a heterozygous long-stemmed plant. Which of the following represents the expected phenotypes of the offspring and the ratio in which they will occur?

1 long-stemmed plant: 1 short-stemmed plant

In sweet pea plants, purple flower color is dominant over red flower color and long pollen grain shape is dominant over round pollen grain shape. Two sweet pea plants that are heterozygous for both flower color and pollen grain shape are crossed with one another. A geneticist is surprised to observe that there are far fewer round, purple offspring and long, red offspring than were predicted by the 9:3:3:1 expected phenotypic ratio.

Which of the following statements provides the most reasonable prediction to account for the deviation from the expected results?

In sweet pea plants, the gene for flower color and the gene for pollen grain shape are genetically linked.

Table 1 shows the stage and number of cells and chromosomes per cell at the end of the stage in a 2n=24 organism.

Table 1. Cell and chromosome count during selected phases of meiosis

Stage	Number of Cells	Number of Chromosomes per Cell
Prophase	1	24
Metaphase	1	24
Anaphase	1	24
Telophase	1	24
Beginning of Prophase II	2	12

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.

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 move single chromatids to each daughter cell.