Study Guide Answers Unit 5

1. interphase
2. Interphase is the time when a cell is not dividing. Most of cell activity occurs during interphase - growth, various metabolic activities, chromosome duplication, organelle duplication, etc.
3. G1 = growth in size, increased enzyme activity.
   S = DNA is replicated.
   G2 = Further growth, an increase in protein synthesis in preparation for mitosis.
4. S phase answers both questions.
5. interphase

Objective 2

1. The nuclear membrane disappears; distinct chromosomes become visible - they are now duplicated, and the nucleolus disappears.
2. The mitotic spindle is fully formed, the duplicated chromosomes are attached to the spindle at their centromeres and the spindle is responsible for the chromosomes lining up along the cell equator. Chromosomes lined up along the cell equator is the typical view at mid-metaphase.
3. The centromeres split and sister chromatids move to opposite poles.
4. Telophase is essentially the opposite of prophase. Chromosomes (no longer duplicated) are at opposite ends of the cell. The nuclear membrane gets established around each chromosome set, the nucleoli reappear, the chromosomes begin to decondense, and cytokinesis occurs.
5. Animal cell division is accomplished by a furrow that divides the cell into two cells; in plant cells a cell plate separates the two new cells.
6. Mitosis produces two new cells that are exactly identical to the parent cell.
7. The spindle moves chromosomes in precise directions during mitosis. In metaphase the spindle lines up the duplicated chromosomes in single file along the cell equator. Then in anaphase, as the centromeres split, the spindle is responsible for the migration of sister chromatids to opposite poles.
   

Objective 3

1. Binary fission is the production of two daughter cells from one parent cell in prokaryotic cells. Because prokaryotes have only one chromosome, the process is much simpler – namely the chromosome attached to the cell membrane duplicates. As the cell enlarges the duplicated chromosomes become further and further apart. A cell plate then partitions the cell into two identical daughter cells and eventually the two cells separate.
2. Prokaryotes.
3. Yes.
   

Objectives 4 and 5 (You are not responsible for these objectives.)

1. benign; malignant
2. metastasis
3. carcinogenic agents
4. cigarette smoke and high energy radiation such as UV light and X-rays
   

The answers to objectives 6 – 22 are found in the Study Guide starting on page Unit 5-24.

Objective 23

1. Pleiotropy occurs when a single gene influences more than one characteristic. An example of pleiotropy is sickle-cell disease which is due to one gene and has many different effects.
2. Polygenic inheritance is a phenotype that results from the expression of many different genes. Any characteristic, such as height in humans, which varies along a continuum is likely due to polygenic inheritance.

Objective 24

1. decrease
2. The diversity of the family’s gene pool would be decreased, and thus the risk for producing children with a common genetic disorder would increase.
3. Undesirable traits would increase in frequency.
4. Hybrid vigor refers to the decreased likelihood of the expression of a harmful phenotype in organisms of a species that have a very diverse gene pool. The chance of an offspring being homozygous for an undesirable trait due to a recessive allele is decreased.