Chapter 9+10 Concept Checks

How many chromosomes are drawn in each part of Figure 9.5?

1 ; 1 ; 2

A chicken has 78 chromosomes in its somatic cells. How many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken's gametes? How many chromosomes will be in each somatic cell of the chicken's offspring?

39 ; 39 ; 78

Compare the life cycles of animals and plants, mentioning their similarities and differences.

Animals and plants both reproduce sexually, alternating meiosis with fertilization. Both have haploid gametes that unite to form diploid zygote, which then goes on to divide mitotically, forming diploid multicellular organism. In animals, haploid cells become gametes and don't undergo mitosis, while in plants, the haploid cells resulting from meiosis undergo mitosis to form haploid gametes. (in plants such as trees, the gametophyte. This organism then goes on in size and not obvious to the casual observer)

Compare and contrast a benign tumor and a malignant tumor.

Both types of tumors consist of abnormal cells, but their characteristics are different: a benign tumor stays at the original site and can usually be surgically removed; the cells have some genetic and cellular changes from normal, non-tumor cells. Cancer cells from a malignant tumor have more significant genetic and cellular changes, can spread from the original site by metastasis, and may impair the functions of one or more organs

Compare the roles of tublin and actin during eukaryotic cell division with the roles of tublin-like and actin-like proteins during binary fission.

During eukaryotic cell division, tublin is involved in spindle formation and chromosome movement, while actin functions during cytokinesis. In bacterial binary fission, its the opposite: tublin-like molecules are thought to act in daughter cell separation, and act-like molecules are thought to move the daughter bacterial chromosomes to opposite ends of the cell

In figure 10.4, how many DNA molecules (double helices) are present (see Figure 9.5)? What is the haploid number of this cell? Is a set of chromosomes haploid or diploid?

Each of the 6 chromosomes is duplicated, so each contain two DNA helices. Therefore, there are 12 DNA molecules in the cell. the haploid number, n, is 3. One set is always haploid.

Compare cytokinesis in animal cells and plants cells.

Following mitosis, cytokinesis results in two genetically identical daughter cells in both plant cells and animal cells. However, the mechanism of dividing the cytoplasm is different in animals and plants. In an animal cell, cytokinesis by cleavage, which divides the part cell in two with a contractile ring of actin filaments. In a plant cell, a cell plate forms in the middle of the cell and grows until its membrane fuses with the plasma membrane of the parent cell. A new cell wall grows inside the cell plate/

During which stage of the cell cycle does a chromosome consist of 2 identical chromatids?

From the end of S phase in interphase through the end of metaphase in mitosis.

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?

If crossing over did not occur, the two homologs would not be associated in any way; each sister chromatid would be either all maternal or paternal, and would only be attached to its sister, not to a non-sister chromatid. This might result in incorrect arrangement of homologs during metaphase I and ultimately in formation of gametes with an abnormal number of chromosomes.

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

If the segments of the maternal and paternal chromatids that undergo crossing over are genetically identical and thus have the same two alleles for every gene, then the recombinant chromosomes will be genetically equivalent to the parental chromosomes. Crossing over contributes to genetic variation only when it involves the rearrangement of different alleles

What phase are most of your body cells in?

Most body cells are in non-dividing state called G0

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

Mutations in a gene can lead to the different alleles of that gene.

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

Parents pass genes to their offspring; by dictating the production of messenger RNAs (mRNAs), the genes program cells to make specific enzymes and other proteins, whose cumulative action produces an individual's inherited traits.

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, should she crossbreed it with another plant or clone it? Why?

She could clone it. Crossbreeding it with another plant would generate offspring that have additional variation, which she no longer desires now that she has obtained her ideal orchid.

how many chromosomes are shown in the drawing in Figure 9.8? Are they duplicated? How many chromatids are shown?

Six chromosomes; they are duplicated; 12 chromatids

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

Such organisms reproduce by mitosis, which generates offspring whose genomes are exact copies of the parent's genome (in absence of mutations)

What would happen if you performed the experiment in Figure 9.17 with cancer cells?

The cells might divide even in the absence of PDGF. In addition, they would not stop when the surface of the culture vessel was covered; they would continue to divide, piling on top of one another

Compare the chromosomes in a cell at metaphase of mitosis with those in a cell at metaphase of meiosis II.

The chromosomes are similar in that each is composed of two sister chromatids, and the individual chromosomes are positioned similarly at the metaphase plate. The chromosomes differ in that in a mitotically dividing cell, sister chromatids of each chromosomes are genetically identical. Also, the chromosomes in metaphase of mitosis can be diploid set or haploid set. But in meiotically dividing cell, sister chromatids are genetically distinct because of the crossing over in meiosis I, but the chromosomes in metaphase of meiosis II always consists of a haploid set.

Each sperm of a pea plant contains seven chromosomes. What are the haploid and diploid numbers for peas?

The haploid number (n) is 7; the diploid number (2n) is 14.

In Figure 9.14, why do the nuclei resulting from experiment 2 contain different amounts of DNA?

The nucleus on the right was originally in the G1 phase; therefore, it had not yet duplicated its chromosomes. The nucleus on the left was in the M phase, so it had already duplicated its chromosomes

In the karyotype shown in Figure 10.3, how many pairs of chromosomes are present? How many sets?

There are 23 pairs of chromosomes and two 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?

This organism has the life cycle shown in Figure 10.6c. Therefore, it must be fungus or protist, perhaps on alga.