Chapter 3: Genetics Concept Questions

The hybrid offspring would have 44 chromsomes (i.e. 25+19). The reason for infertility is because each chromosome does not have a homologous partner. Therefore, the chromosomes cannot properly pair during metaphase I, and the gametes do not receive one copy of each homolog. Gametes will be missing certain chromosomes, which makes them infertile.

The arctic fox has 50 chromosomes (25 per set), and the common red fox has 38 chromosomes (19 per set). These species can interbreed to produce viable but infertile offspring. How many chromosomes would the offspring have? What problems do you think may occur during meiosis that would explain the offspring's infertility?

It means that the maternally derived and paternally derived chromosomes are randomly aligned along metaphase plate during metaphase I.

The arrangement of homologs during metaphase of meiosis I is a random process. In your own words, explain what this means.

X XX X X XX X X X XX X X X A B C A.) mitosis B.) meiosis I C.) meiosis II

A cell is diploid and contains three chromosomes per set. Draw the arrangement of chromosomes during metaphase of mitosis and metaphase of meiosis I and II. In your drawing, make one set dark and the other lighter.

During prophase II, your drawing should show four replicated chromosomes (i.e. four structures that look like Xs). Each chromosome is one homog. During prophase of mitosis, there should be eight replicated chromosomes. During prophase of mitosis, there are pairs of homologs. The main difference is that prophase II has a single copy of each of the four choromosomes, whereas prophase of mitosis has four pairs of homologs. At the end of meiosis I, each daughter cell has received only one copy of homogous pair, not both. This is due to the alignment of homlogs during metaphase I and their separation during anaphase I.

A diploid species has four chromosomes per set for a total of eight chromosomes in its somatic cells. Draw the cell as it would look in late prophase of meiosis II and prophase of mitosis. Discuss how prophase of meiosis II and prophase of mitosis differ from each other, and explain how the difference originates.

For mitosis, two diploid cells containing 10 chromosomes each (two complete sets). For meiosis, four haploid cells produced containing 5 chromosomes each (one complete set).

A eukaryotic cell is diploid containing 10 chromosomes (5 in each set). For mitosis and meiosis, how many daughter cells would be produced, and how many chromosomes would each one contain?

In G1, there should be six linear chromosomes. In G2, there should be 12 chromatids that are attached to each other in pairs of sister chromatids.

A species is diploid and has three chromosomes per set. Draw what the chromosomes would look like in the G1 and G2 phases of the cell cycle.

The reduction occurs because there is a single DNA replication event but two cell divisions. Because of the nature of separation during anaphase I, each cell receives one copy of each type of chromosome.

Describe the key events during meiosis that result in a 50% reduction in the amount of genetic material per cell.

Bacteria do not need to sort their chromosomes because they only have one type of chromosome.

Eukaryotic cells must sort their chromosomes during mitosis so each daughter cell receives the correct number of chromosomes. Why don't bacteria need to sort their chromosomes?

The products of meiosis have only one copy of each type of chromosome. For example, one human gamete may contain the paternally derived copy of chromosome 11, whereas a different gamete may contain the maternally derived copy of chromosome 11. These two homologs may carry different alleles of the same genes and therefore are not identical. In contrast, mitosis produces genetically identical daughter cells that have both copies of all the pairs of homologous chromosomes.

Explain why the products of meiosis may not be genetically identical, whereas the products of mitosis are.

A. mitosis, meiosis I B. meiosis I C. mitosis, meiosis I, meiosis II D. mitosis, meiosis II

For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: A. Separation of conjoined chromatids within a pair of sister chromatids B. Pairing of homologous chromosomes C. Alignment of chromatids along the metaphase plate D. Attachment of sister chromatids to both poles

2^3 = 8 random arrangements

If a diploid cell contains six chromosomes (i.e., three per set), how many possible random arrangements of homologs could occur during metaphase of meiosis I?

To produce identical quadruplets, fertilization begins with one sperm and one egg cell. This fertilized egg then could divide twice by mitosis to produce four genetically identical cells. These four cells could then separate from each other to begin the lives of four distinct individuals. Another possibility is that mitosis could produce two cells that separate from each other. These two cells could then divide by mitosis to produce two pairs of cells, which could also separate to produce four individual cells.

Nine-banded armadillos almost always give birth to four offspring that are genetically identical quadruplets. Explain how you think this happens

No

The period between meiosis I and meiosis II is called interphase II. Does DNA replication take place during interphase II?

Homolog refers to the members of a chromosome pair. Homologs are usually the same size and carry the same types and order of genes. They may differ in that the genes they carry may be different alleles.

What is a homolog? With regard to genes and alleles, how are homologs similar to and different from each other?

Sister chromatids are identical copies derived from the replication of a parental chromosome. They remain attached to each other at the centromere. They are genetically identical, barring rare mutations and crossing over with homologous chromosomes.

What is a sister chromatid? Are sister chromatids genetically similar or identical? Explain.

During interphase, the chromosomes are greatly extended. In this conformation, they might get tangled up with each other and not sort properly during meiosis and mitosis. The condensation process probably occurs so that the chromosomes easily align along the equatorial plate during metaphase without getting tangled up.

Why is it necessary for the chromosomes to condense during mitosis and meiosis? What do you think might happen if the chromosomes were not condensed?