Test: Meiosis (NCERT)


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QUESTION: 1

To build up food reserves in the cytoplasm, chromosomes become unfolded to start transcription of mRNA and rRNA, during which phase of meiosis I? 

Solution:

In diplotene stage of meiosis I, the chromosomes may unfold to nearly form and start transcription of mRNA and rRNA to build up food reserves in the cytoplasm. This process is most pronounced in the primary oocytes of amphibians, reptiles and birds. In some species, the chromosomes enlarge greatly, assuming lampbrush form.

QUESTION: 2

During meiosis -I, chromosome number?

Solution:

Meiosis is the type of cell division by which gamete cells (eggs and sperm) are produced. Meiosis involves two successive nuclear divisions and one cytoplasmic division that produce four haploid cells. The first division (meiosis 1) is the reductional division during which number of chromosomes is reduced to half. The second division (meiosis II) separates the chromatids. It is called equational division as chromosome number remains the same as produced after meiosis-l.

QUESTION: 3

At which of the following stages, the chromosomes appear single, thin and thread like?

Solution:

Leptotene also known as leptonema is the first stage of prophase I during which individual chromosomes begin to condense into long strands within the nucleus which are loossely interwoven. However, the two sister chromatids are still so tightly bound that they are indistinguishable from one another. They possess a string of swollen areas called chromomeres.

QUESTION: 4

Best material to study meiosis is

Solution:

Meiosis takes place in reproductive organs. It results in formation of gametes with half the normal chromosome number. Young anthers are the best material to study meiosis.

QUESTION: 5

Crossing over in diploid organism is responsible for

Solution:

Crossing over is a process of exchange of genetic material between non-sister chromatids of two homologous chromosomes and and leads to recombination of genes. It is an enzyme mediated process.

QUESTION: 6

Lampbrush chromosomes are seen in which typical stage?

Solution:

The lampbrush chromosomes occuring in prophase of meiosis II are highly elongated special kind of synapsed mid-prophase or diplotene chromosome bivalents which have already undergone crossing over. Lampbrush chromosomes occur in pairs. Each chromosome of a pair has a double main axis due to presence of two elongated chromatids. Both the adjacent chromatids bear rows of large number of chromomeres. Two adjacent chromomeres are separated by interchromomeric stretches. Many of the chromomeres give out lateral projections or loops. The lateral loops provide a test tube or lampbrush-like appearance to the chromosome pair. Lateral loops take part in rapid transcription of DNA to mRNA meant for synthesis of yolk and other substances required for growth and development of Meiocyte.

QUESTION: 7

Identify the given figures showing meiotic phases and select the correct option.

Solution:

All the stages are of the meiosis 1 because here we can see the bivalent or tetrad stages. Metaphase is the stage where chromosome comes on the equator and bivalent arrange themselves on the equatorial plate. Then anaphase 1 involves the separation of a homologous chromosome which start moving up to opposite poles and each tetrad is divided into two daughter cells. So anaphase involves the production of chromosome number and is also known as disjunction. Telophase 1 shows the formation of two daughter nuclei but the chromosome number is half then the chromosome number of mother cell and nuclear membrane reappears.

QUESTION: 8

An anther has 1200 pollen grain. How many PMCs must have been there to produce them?

Solution:

Meiosis of one Pollen Mother Cell (PMC) produces 4 haploid pollen grains. Thus, for producing 1200 pollen grains 1200/4=300 PMCs are required.

QUESTION: 9

If 2n = 4, then identify the figures A, B and C, as per the following codes and select the correct option.

 Anaphase of meiosis I = (i)
 Anaphase of mitosis = (ii)
 Anaphase of meiosis II = (iii)

Solution:

During anaphase of mitosis, each chromosome arranged at metaphase plate is split and two daughter chromatids are formed. Centromeres split and chromatids move to opposite poles. During anphase I of meiosis I, the homologous chormosomes separate, while sister chromatids remain associated at their centromeres. Anaphase II of meiosis II begins with simultanoeus splitting of the centromere of each chromosome allowing them to move towards oppostie poles of the cell.

QUESTION: 10

What does (i) and (ii) represent in the given flowchart?

Solution:

Meiosis I consists of separation of the homologous chromosomes, each made up of two sister chormatids into two cells. Entire haploid content of chomosomes is contained in each of the resulting daughter cells. The first meiotic division therefore reduces the ploidy of the original cell by a factor of 2. Meiosis II consists of decoupling of each chormosome sister strands (chromatids) and segregating the individual chromatids into haploid daughter cells. The two cells resulting from meiosis I divide during meiosis II, creating 4 haploid daughter cells.

QUESTION: 11

During meiosis - I in humans, one of the daughter cells receives

Solution:

During pachytene sub-stage of meiosis I, crossing over i.e. exhcnage of genetic material takes place between homologous, which results in recombinations. The two homologous chromosomes are contributed by different parents. One of them is partnerl chromosome and the other one is maternal chormosome.

QUESTION: 12

The members of a homologous pair of chromosomes

Solution:

Homologous chormosomes are chormosomes having same structural features. In dipilod nuclei, pairs of homologous chromosomes can be identified at the start of meiosis. One member of each pair comes from the female parent and other from the male parent. Homologous chromosomes have the same pattern of genes along the chromosome but the nature of the genes may differ.

QUESTION: 13

The figure given below shows a cell undergoing meiosis.


Which of the options below shows the next stage in the process?

Solution:

The given figure is showing diplotene stage of prophase I of meiosis I. Next stage would be metaphase I.

QUESTION: 14

 Consider the given cellat metaphase-I stage undergoing normal meisois.

Which of the following gametes will not be formed from this cell?

Solution:
QUESTION: 15

Four different steps that occur during meiosis are given in the following list.
(i) Complete separation of chromatids
(ii) Pairing of homologous chromosomes 
(iii) Lining up of paired chromosomes on equator
(iv) Crossing over between chromatids
Select the correct sequential arrangement of the steps.

Solution:

Pairing of homologous chromosomes occurs in zygotene and crossing over occurs in pachytene stage of prophase I of meiosis I. Paired chromosomes line up on equator in metaphase I. Then there is complete separation of chromatids in anaphase I of meiosis I.

QUESTION: 16

Meiosis consists of 

Solution:

Meiosis is a double division that occurs in the reproductive cell in which nucleus divide but chromosome replicate only once to form four haploid cells, each cell having half the number of chromosomes present in a parent cell. It causes a reduction in the number of chromosomes. It is also known as reduction division. Meiosis in a cell occurs only once to form gametes.

QUESTION: 17

While in mitosis, the daughter cells resemble each other and also the parent cell; in meiosis they differ not only from parent cell in having half the number of chromosomes, but also differ among themselves qualitatively in genetic constitution due to

Solution:
QUESTION: 18

Disjunction refers to

Solution:

The homologous chromosomes break their connections and separate out during anaphase I of meiosis I. This process of separation is named as disjunction.

QUESTION: 19

At what phase of meiosis there are two cells, each with separated sister chromatids that have been moved to opposite spindle poles?

Solution:

Anaphase II, where the centromeres are cleaved, allows the kinetochores to pull the sister chromatids apart. The sister chromatids by convention are now called sister chromosomes and they are pulled towards opposte poles.

QUESTION: 20

If gametes are produced after reduction division, they are termed as

Solution:

Reduction divison is known as meiosis, gametes foremed from this divison are known as meiogametes.

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