genetics 2 - meiosis

Question 1

What is a homologous chromosome?

Answer 1

Two chromosomes carrying the same genes but not the same alleles. One is originated from the sperm, and the other is originated from the ovum.

Question 2

What is a chiasma?

Answer 2

The point of contact between two chromatids exchanging genetic information

Question 3

What is meiosis?

Answer 3

A special cell division that occurs in the germ cells for reproductive purposes

Question 4

What are the two processes of meiosis?

Answer 4

Genetic reduction and genetic recombination

Question 5

Where does meiosis occur?

Answer 5

The ovaries/testes

Question 6

What does meiosis create?

Answer 6

Genetically different haploid gametes.

Question 7

What is fertilization?

Answer 7

The fusion of haploid male and female gametes which forms a diploid zygote

Question 8

What is a zygote?

Answer 8

A group of cells that are going to become the child

Question 9

What happens in interphase?

Answer 9

G1, S, and G2 phases occur before meiosis. DNA replication takes place, parent cells contain duplicated chromosomes, and the sister chromatids are held together at the centromere.

Question 10

What happens in prophase I?

Answer 10

Synapsis, the homologous chromosomes cross-over to exchange genes, the chromatin condense. The cell has two centrosomes which move to the poles and form mitotic spindles.

Question 11

What happens in Metaphase I?

Answer 11

The spindle fibres attach to the centromere of each chromosome, and the homologous pairs of chromosomes line up at the equatorial plate. The chromosomes of maternal and paternal origins are at opposite poles.

Question 12

What does the chromosomes lining up have to do with gametes?

Answer 12

Depending on how the pairs of homologous chromosomes line up, you can have a different number of combinations of the genetically distinct gametes (2^n, n=number of haploid chromosomes). Since humans have 23 haploid chromosomes, we can make up to 2^23 combinations=8,366,608

Question 13

What happens in anaphase I?

Answer 13

The homologous chromosomes separate to opposite poles of the cell and are pulled apart by the shortening of the spindle fibres. Here, it goes from diploid to haploid (92 chromatids –> 46 chromatids, 46 chromosomes –> 23 chromosomes)

Question 14

What happens in telophase I?

Answer 14

The homologous chromosomes uncoil and the spindle fibres disappear. The nuclear envelope and nucleolus reappear, and cytokinesis follows.

Question 15

When does DNA duplication take place?

Answer 15

During the S phase of interphase.

Question 16

When does synapsis occur? Prophase I

Answer 16

Prophase I

Question 17

When do chromatids condense?

Answer 17

Prophase I and II

Question 18

When do homologous chromosomes cross-over to exchange genetic information?

Answer 18

Prophase I

Question 19

When do the two centrosomes move to the poles and form mitotic spindles?

Answer 19

Prophase I and II

Question 20

When do spindle fibres attach to the centromere of each chromosome?

Answer 20

Metaphase I

Question 21

When do the pairs of homologous chromosomes line up at the equatorial plate?

Answer 21

Metaphase I

Question 22

When do the chromosomes of maternal and paternal origins go to different poles?

Answer 22

Metaphase I

Question 23

When do the homologous chromosomes separate to opposite poles of the cell?

Answer 23

Anaphase I

Question 24

When are the homologous chromosomes pulled apart by the shortening of spindle fibres?

Answer 24

Anaphase I

Question 25

When do the chromosomes and chromatids go from diploid to haploid?

Answer 25

Anaphase I

Question 26

When does the nuclear envelope and nucleolus reappear?

Answer 26

Telophase I

Question 27

When do the homologous chromosomes uncoil?

Answer 27

Telophase I

Question 28

When do the spindle fibres disappear?

Answer 28

Telophase I

Question 29

What happens to the chromosomes and chromatids after anaphase I?

Answer 29

92 chromatids --> 46 chromatids 46 chromosomes --> 23 chromosomes Diploid --> Haploid

Question 30

Difference between meiosis I and II?

Answer 30

During meiosis I homologous chromosomes separate, and in meiosis II, sister chromatids separate

Question 31

During meiosis, genetic variation in the gametes is achieved by

Answer 31

Crossing over and independent assortment

Question 32

What happens in prophase II?

Answer 32

The chromatin coils to condense into chromosomes, the centrosomes appear at opposite ends of the cell and form spindle fibres, and the nuclear membrane and nucleolus disappear

Question 33

Difference between prophase I and II?

Answer 33

Prophase I includes the separation of homologous chromosomes, while prophase II involves the separation of sister chromatids. In prophase I, homologous chromosomes cross-over, while they don't in prophase II.

Question 34

What causes genetic variation?

Answer 34

Crossing-over and independent assortment of homologous chromosomes and chromatids.