6.3 Meiosis

Question 1

What is a diploid cell?

Answer 1

Cell with 2 chromosomes of each type

Question 2

How does sexual reproduction take place?

Answer 2

2 gametes, one from each parent, fuse to make a fertilised egg
This zygote is the origin of all the cells that the organism develops
Gametes should only contain half the number of chromosomes in a cell

Question 3

How are gametes formed?

Answer 3

By meiosis

Question 4

Why is meiosis known as reduction division?

Answer 4

Each gamete contains half the chromosome number of the parent cell - it is haploid

Question 5

Homologous chromosomes

Answer 5

Matching pair of chromosomes, one inherited from each parent

Question 6

Alleles

Answer 6

Different versions for the same gene

Different alleles of a gene will all have the same locus (position on a particular chromosome)

Question 7

2 stages of meiosis

Answer 7

Meiosis 1

Meiosis 2

Question 8

Meiosis 1

Answer 8

First division is reduction division

Pairs of homologous chromosomes are separated into 2 cells

Question 9

Meiosis 2

Answer 9

Second division is similar to mitosis
Pairs of chromatids present in each daughter cell are separated, forming 2 more cells
4 haploid cells daughter cells are produced in total

Question 10

Prophase 1

Answer 10

Chromosomes condense, nuclear envelope disintegrates
Nucleolus disappears and spindle formation begins

Homologous chromosomes pair up, forming bivalents
While moving through the cytoplasm, chromatids become entangled - causing crossing over

Question 11

Metaphase 1

Answer 11

Similar to metaphase in mitosis
Homologous pairs of chromosomes assemble along metaphase plate instead of individual chromosomes
Orientation of homologous chromosomes is random
This is called independent assortment - can have many different combinations of alleles facing the poles

Question 12

What stage in meiosis causes genetic variation?

Answer 12

Metaphase 1

Question 13

Anaphase 1

Answer 13

Homologous chromosomes are pulled to opposite poles and chromatids stay joined to each other
Sections on sister chromatids become entangled and cross over, break off and rejoin, causing exchange in DNA
Forms recombinant chromatids, so there are different allele combinations causing genetic variation

Question 14

Chiasmata

Answer 14

Points where chromatids break and rejoin

Question 15

Telophase 1

Answer 15

Chromosomes assemble at each pole
Nuclear membrane reforms
Chromosomes uncoil
Cell undergoes cytokinesis

Question 16

Prophase 2

Answer 16

Chromosomes, which still have 2 chromatids condense and become visible
Nuclear envelope breaks down and spindle formation begins

Question 17

Metaphase 2

Answer 17

Individual chromosomes assemble on the metaphase plate

Due to crossing over, chromatids are no longer identical, so there is independent assortment and more genetic variation

Question 18

Anaphase 2

Answer 18

Chromatids of individual chromosomes are pulled to opposite poles after division of centromeres
Same as anaphase in mitosis

Question 19

Telophase 2

Answer 19

Chromatids assemble at poles
Chromosomes uncoil to form chromatin again
Nuclear envelope reforms and nucleolus becomes visible
Cytokinesis occurs, forming 4 daughter cells in total (haploid due to reduction division)