Ch.13 Sample Questions- Mieosis
1. A horticulturalist breeds orchids, trying to obtain a plant with a unique
combination of desirable traits. Atrer many years, she finally succeeds. To
produce more plants like this one, should she cross-breed it with another
plant or clone it? Why?
2. How does the alternation of meiosis and fertilization in the life cycles of
sexually reproducing organisms maintain the normal chromosome count for
each species?
3. Each sperm of a pea plant contains seven chromosomes. What are the
haploid and diploid numbers for this species?
4. How are the chromosomes in a cell at metaphase of mitosis similar to and
different from the chromosomes in a cell at metaphase of meiosis II?
5. What is the original source of variation among the different alleles of a gene?
6. Under what circumstances would crossing over during meiosis not
contribute to genetic variation among daughter cells?
7. 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.
8. The continuity of life is based on heritable information in the form of DNA.
Explain how chromosome behavior during sexual reproduction in animals
ensures perpetuation of parental traits in offspring and, at the same time,
genetic variation among offspring.
Ch.13 Sample Questions- Meisosis- Answers
1. She should clone it. Cross-breeding it with another plant would generate
offspring that have additional variation, which she no longer desires, now that
she has obtained her ideal orchid.
2. In meiosis, the chromosome count is reduced from diploid to haploid; the union
of two haploid gametes in fertilization restores the diploid chromosome count
3. The haploid number (n) is 7, the diploid number (2n) is 14
4. 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 ce..,
sister chromatids of each chromosomes are genetically identical, but in a
meiotically dividing cell, sister chromatids are genetically distinct because of
crossing over in meiosis I. Moreover, the chromosomes in metaphase of mitosis
can be a diploid set or a haploid set, but the chromosomes in metaphase of
meiosis II always consist of a haploid set.
5. Mutations in a gene lead to the different versions (alleles) of that gene.
6. 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.
7. Asexual reproduction creates a lot of offspring that are clones, the unfavorable
environment may not support large numbers of offspring, in addition, these
clones may not be well adapted to the unfavorable environment. However,
sexual reproduction creates variations, and if all the offspring were genetically
different, there may be varieties that are better suited to the unfavorable
environment, which could surivive and reproduce.
8. Offspring inherit 50% of their genes from each parent. Each gene is the
offspring is composed of 2 alleles, one from each parent. The offspring may
take on the characteristic of one or the other, or a combination of both parents.