Question

7. What are chiasmata in a nucleus going through meiosis?

a. they are sites where non-sister chromatids can exchange genetic material during meiosis.

b. they are sites where sister chromatids can exchange genetic material during meiosis.

c. they ensure that homologous chromosomes remain homologous after meiosis.

d. they increase genetic variation among the products of mitosis.

e. they prevent sister chromatids from separating.

8. A chromatid is:

a. one of the pairs of homologous chromosomes.

b. a homologous chromosome.

c. a newly replicated bacterial chromosome.

d. one half of a newly replicated eukaryotic chromosome.

e. a pair of newly synthesized chromosomes.

9. How does a nucleus in the G2 differ from a nucleus in G1?

a. the G2 nucleus has double the amount of DNA as a G1 nucleus.

b. DNA synthesis occurs only in the G1 phase.

c. inactive cells are arrested only in the G2 phase.

d. during G2, the cell prepares for S phase.

e. all of the above.

10. The major drawback of asexual reproduction, as compared to sexual reproduction, is that it

a. takes a great deal of time.

b. generates variation.

c. requires cytokinesis.

d. produces less variation among offspring.

e. None of the above; there are no major drawbacks associated with asexual reproduction.

11. The diagnosis of Down syndrome is made by examining the individual’s

a. spores.

b. karyotype.

c. chromatin.

d. nucleosomes.

e. kinetochores.

12. The fact that most monosomies and trisomies are lethal to human embryos illustrates the

a. importance of the orderly distribution of genetic material during meiosis.

b. exchange of genetic information during crossing over.

c. advantage of sexual reproduction to the survival of a population.

d. fact that each chromosome contains a single molecule of DNA.

e. formation of haploid gametes as a result of meiosis.

Answer 1

7. A

Crossing over is the process of exchange of genetic material between non sister chromatids of homologous chromosomes. It occurs during prophase 1 of meiosis 1. It occurs with the help of formation of chiasmata. Chiasmata is a cross like structure seen during prophase representing chromosomes undergoing crossing over.

8. D

See structures below to get a clarity on chromatid, chromosomes, homologous structure, chromatin -

9. A

G1 is gap 1 phase in which the cell prepares itself to divide. It has x number of chromosomes and chromatids and c amount of DNA.

S is synthesis phase in which DNA is duplicated. The number of chromosomes is c but chromatids are 2c. The amount of DNA is 2c.

In G2 phase, the cell prepares itself to divide. The number of chromosomes is c, chromatids is 2c. Tje amount of DNA is 2c.

10. D

Asexual reproduction	Sexual reproduction
No formation and fusion of gametes	Occurs by formation and fusion of gametes
No genetic variations	Leads to genetic variations
Takes less time	Takes more time
Produces a large number of progenies at one time	Produces one to very few progenies at one time

11. B

Karyotype is a pictorial representation of chromosomes of a cell of an individuals. It is prepared by taking picture of metphasic chromosomes. The chromosomes are arranged in decreasing order of their size, sex chromosomes come at the end.

Karyotype is used to study the following -

Sex of the individual

Translocation

Monosomy

Trisomy (down syndrome)

Banding pattern of chromosomes

Number of chromosomes in an organism

Shape and size of chromosomes etc.

12. E

Monosomy and trisomy results in one copy less and one copy extra of chromosome respectively. It results in drastic change in gene dosage amd therefore, alters the phenotype to a great extent.

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