2.12

Question 1

Gametes are made by

Answer 1

meiosis

Question 2

Meiosis is a

Answer 2

2-stage division in which a diploid cell divides to produce 4 haploid gametes

Question 3

ORDER OF MEIOSIS:

Answer 3

INTERPHASE
PROPHASE I 
METAPHASE I
ANAPHASE I
TELOPHASE I 
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II

Question 4

Interphase:

Answer 4

immediately before meiosis

DNA replicates so that the cell now contains 4 rather than 2 copies of each chromosome

Question 5

Prophase I (4 stages):

Answer 5

• Chromosomes shorten and fatten and come together in their homologous pairs to form a BIVALENT
• Chromatids wrap around one another and attach at points called CHIASMATA
• Chromosomes break at these points and swap similar sections of chromatids with one another in a process called CROSSING OVER
• Nucleolus disappears and the nuclear envelope disintegrates

Question 6

Metaphase I (2 stages):

Answer 6

• Centromeres attach to the spindle
• Bivalents arrange themselves randomly on the equator of the cell with each of a pair of homologous chromosomes facing opposite poles

Question 7

Anaphase I:

Answer 7

-One of each pair of homologous chromosomes is pulled by spindle fibres to opposite poles

Question 8

Telophase I:

Answer 8

-A nuclear envelope re-forms around the chromosomes at each pole (in most animal cells)
(in most plant cells there is no telophase I, cell directly goes into metaphaseII)

Question 9

Prophase II (4 stages):

Answer 9

• Where the nuclear envelope has re-formed it breaks down again
• Nucleolus disappears
• Chromosomes shorten and thicken
• Spindle re-forms

Question 10

Metaphase II:

Answer 10

-Chromosomes arrange themselves on the equator of each cell

Question 11

Anaphase II (2 stages):

Answer 11

• Centromeres divide

- Chromatids are pulled to opposite poles by the spindle fibres

Question 12

Telophase II (3 stages):

Answer 12

• The tetrad of 4 cells is formed
• Each cell has the haploid number of chromosomes
• Crossing over during prophase I has produced genetic variety

Question 13

Bivalents are:

Answer 13

The pair of homologous chromosomes that pair and form chiasmata in the first division of meiosis

Question 14

Chiasmata are:

Answer 14

The places at which the chromatids of homologous chromosomes wrap around each other and exchange pieces

Question 15

The first division of meiosis involves the homologous chromosomes pairing together to form a

Answer 15

bivalent

Question 16

Chromatids of homologous chromosomes wrap around each other at places called

Answer 16

chiasmata

Question 17

At chiasmata, chromatids break and equivalent pieces of chromatids are exchanged. This process is called

Answer 17

crossing over

Question 18

The second division of meiosis is like mitosis. In this stage the chromatids

Answer 18

separate from each other

Question 19

Meiosis brings about variation in 3 ways:

Answer 19

• Crossing over during prophase I produces new combinations of alleles
• Independent assortment of homologous chromosomes - in M1 pairs of homologous chromosomes line up on the spindle randomly, each pair separates independently of any other pair, assortment occurs in anaphase 1
• Independent assortment of chromatids in anaphase 2 again occurs randomly, so each pair of chromatids separates independently of any other pair

Question 20

Another source of variation occurs at

Answer 20

fertilisation

Question 21

(Fertilisation) each gamete produced by an individual is genetically different from any other. There are usually many different male gametes, and it is purely random which one of these will fertilise the oocyte. As a result, the genetic make-up of every new individual is

Answer 21

unique