Meiosis and Sexual Life Cycles

Given the fact that 1 fg of DNA = 9.78 × 10⁵ base pairs (on average), you can convert the amount of DNA per cell to the length of DNA in numbers of base pairs. (a) Calculate the number of base pairs of DNA in the haploid yeast genome. Express your answer in millions of base pairs (Mb), a standard unit for expressing genome size. Show your work. (b) How many base pairs per minute were synthesized during the S phase of these yeast cells?

Using what you know of gene expression in a cell, explain what causes the traits of parents (such as hair color) to show up in their offspring. (See Concept 5.5)

How does an asexually reproducing eukaryotic organism produce offspring that are genetically identical to each other and to their parents?

A horticulturalist breeds orchids, trying to obtain a plant with a unique combination of desirable traits. After many years, she finally succeeds. To produce more plants like this one, she should crossbreed it with another plant or clone it. Why?

In Figure 13.4, how many DNA molecules (double helices) are present (see Figure 12.5)? What is the haploid number of this cell? Is a set of chromosomes haploid or diploid?

In the karyotype shown in Figure 13.3, how many pairs of chromosomes are present? How many sets?

A certain eukaryote lives as a unicellular organism, but during environmental stress, it produces gametes. The gametes fuse, and the resulting zygote undergoes meiosis, generating new single cells. What type of organism could this be?

Given the fact that 1 fg of DNA = 9.78 × 10⁵ base pairs (on average), you can convert the amount of DNA per cell to the length of DNA in numbers of base pairs. (a) Calculate the number of base pairs of DNA in the haploid yeast genome. Express your answer in millions of base pairs (Mb), a standard unit for expressing genome size. Show your work. (b) How many base pairs per minute were synthesized during the S phase of these yeast cells?

First, set up your graph. (a) Place the labels for the independent and dependent variables on the appropriate axes, followed by units of measurement in parentheses. Explain your choices. (b) Add tick marks and values for each axis. Explain your choices.

Because the variable on the x-axis varies continuously, it makes sense to plot the data on a line graph. (a) Plot each data point from the table onto the graph. (b) Connect the data points with line segments.

Most of the yeast cells in the culture were in G₁ of the cell cycle before being moved to the nutrient-poor medium. (a) How many femtograms of DNA are there in each yeast cell in G1? Estimate this value from the data in your graph. (b) How many femtograms of DNA should be present in each cell in G2? (See Concept 12.2 and Figure 12.6.) At the end of meiosis I (MI)? At the end of meiosis II (MII)? (See Figure 13.7.) (c) Using these values as a guideline, distinguish the different phases by inserting vertical dashed lines in the graph between phases and label each phase (G₁, S, G2, MI, MII). You can figure out where to put the dividing lines based on what you know about the DNA content of each phase (see Figure 13.7). (d) Think carefully about the point where the line at the highest value begins to slope downward. What specific point of meiosis does this “corner” represent? What stage(s) correspond to the downward sloping line?

After the synaptonemal complex disappears, how would any pair of homologous chromosomes be associated if crossing over did not occur? What effect might this have on gamete formation?

Compare the chromosomes in a cell at metaphase of mitosis with those in a cell at metaphase II. (See Figures 12.7 and 13.8.).

What is the original source of variation among the different alleles of a gene?

The diploid number for fruit flies is 8, and the diploid number for grasshoppers is 46. If no crossing over took place, would the genetic variation among offspring from a given pair of parents be greater in fruit flies or grasshoppers? Explain.

If maternal and paternal chromatids have the same two alleles for every gene, will crossing over lead to genetic variation?

A human cell containing 22 autosomes and a Y chromosome is 

1. sperm
2. an egg
3. zygote
4. a somatic cell of a male

The two homologs of a pair move toward opposite poles of dividing cells during 

1. mitosis
2. meiosis I
3. meiosis II
4. fertilization

Meiosis II is similar to mitosis in that

1. sister chromatids separate during anaphase
2. DNA replicates before the division.
3. the daughter cells are diploid.
4. homologous chromosomes synapse

If the DNA content of a diploid cell in the G₁ phase of the cell cycle is x, then the DNA content of the same cell at the metaphase of meiosis I will be

1. 0.25x
2. 0.5x
3. x
4. 2x

If we continue to follow the cell lineage from question 4, then the DNA content of a single cell at metaphase of meiosis II will be

1. 0.25x
2. 0.5x
3. x
4. 2x

The diagram shows a cell in meiosis. 

1. Label the appropriate structures with these terms: chromosomes (label as duplicated or unduplicated), centromere, kinetochore, sister chromatids, non-sister chromatids. Homologous pair (use a bracket when labeling), homolog (label each one), chiasma sister chromatid cohesion, and gene loci, labeling the alleles of the F and H genes.
2. Describe the makeup of a haploid set and a diploid set.
3. Identify the stage of meiosis shown.

Explain how you can tell that the cell in question 6 is undergoing meiosis, not mitosis.

Many species can reproduce either asexually or sexually. Explain what you think might be the evolutionary significance of the switch from asexual to sexual reproduction that occurs in some organisms when the environment becomes unfavorable.

The diagram in question 6 represents just a few of the chromosomes of meiotic cells in a certain person. Assume the freckles gene is located at the locus marked F, and the hair color gene is located at the locus H, both on the long chromosome. The individual from whom this cell was taken has inherited different alleles for each gene ("freckles" and "black hair" from one parent, and "no freckles" in the gametes resulting from this meiotic event. (It will help if you draw out the rest of meiosis and label the alleles by name.) List other possible combinations of these alleles in this individual's gametes. 

The continuity of life is based on heritable information in the form of DNA. IN a short essay (100-150 words), explain how chromosome behavior during sexual reproduction in animals ensures the perpetuation of parental traits in offspring and, at the same time, genetic variation among offspring. 

The Cavendish banana, the world’s most popular fruit, is threatened by extinction due to a fungus. This banana variety is "triploid" (3n, with three chromosomes) and can only reproduce through cloning by cultivators. Given what you know about meiosis, please explain how the banana's triploid numbers account for its inability to form a normal gamete. Considering genetic diversity, discuss how the absence of sexual reproduction might make this domesticated species vulnerable to infectious agents.