9.2- MEIOSIS AND GENETIC VARIATION

Question 1

In what ways can cell division occur? (2)

Answer 1

mitosis

meiosis

Question 2

What does mitosis produce?

Answer 2

two daughter cells with same number of chromosomes as parent cell as each other

Question 3

What does meiosis usually produce?

Answer 3

four daughter cells, each with half the number of chromosomes as parent cell

Question 4

What do two gametes do in sexual reproduction?

Answer 4

two gametes fuse to give rise to new offspring

Question 5

What is the diploid number of chromosomes in humans?

Answer 5

46

Question 6

Why must the number of chromosomes be halved at some stage in the cycle?

Answer 6

to maintain constant number of chromosomes in adults of species

Question 7

What does the halving of the number of chromosomes occur due to?

Answer 7

meiosis

Question 8

In most animals when does meiosis occur?

Answer 8

in formation of gametes

Question 9

In some plants i.e. ferns, how are gametes produced?

Answer 9

by mitosis

Question 10

In the fern (type of plant) life cycle, when does meiosis occur?

Answer 10

in formation of spores

Question 11

What does every diploid cell of organism have?

Answer 11

two complete sets of chromosomes: one set provided by each parent

Question 12

What happens to homologous pairs during meiosis?

Answer 12

homologous pairs of chromosomes separate, so only one chromosome from each pair enters daughter cell

Question 13

What is the haploid number of chromosomes in humans?

Answer 13

23

Question 14

What happens when two haploid gametes fuse at fertilisation?

Answer 14

diploid number of chromosomes restored

Question 15

How many nuclear divisions does meiosis involve?

Answer 15

two nuclear divisions

Question 16

What happens in the first division (meiosis 1)?

Answer 16

homologous chromosomes pair up + their chromatids wrap around each other
equivalent portions of these chromatids may be exchanged in crossing over

Question 17

What happens by the end of the first division (meiosis 1)?

Answer 17

homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells

Question 18

What happens in the second meiotic division (meiosis 2)?

Answer 18

chromatids move apart

Question 19

What happens by the end of the second meiotic division (meiosis 2)?

Answer 19

four cells have usually been formed

in humans each of these cells contain 23 chromosomes

Question 20

What does meiosis produce among the offspring?

Answer 20

genetic variation

Question 21

What can the genetic variation among offspring from meiosis lead to?

Answer 21

adaptations that improve survival chances

Question 22

How does meiosis bring about genetic variation? (2)

Answer 22

independent segregation of homologous chromosomes

new combinations of maternal + paternal alleles by crossing over

Question 23

What is a gene?

Answer 23

length of DNA that codes for polypeptide

Question 24

What is the locus?

Answer 24

position of gene on chromosome or DNA molecule

Question 25

What is an allele?

Answer 25

one of the different forms of a particular gene

Question 26

What are homologous chromosomes?

Answer 26

pair of chromosomes, on maternal + one paternal that have same gene loci

Question 27

What does each chromosome do during meiosis 1?

Answer 27

each chromosomes lines up alongside its homologous partner

Question 28

In what way do each chromosome arrange themselves when they line up alongside its homologous partner during meiosis 1?

Answer 28

do so at random

Question 29

What happens to each of the homologous pair when they line during meiosis 1?

Answer 29

one of each pair will pass to each daughter cell

Question 30

How is where which pair of the homologous pair from meiosis 1 determined?

Answer 30

which one of pair goes into daughter cells, and with which one of any of other pairs, depends on how pairs lined up in parent cell

Question 31

Why is the combination of chromosomes of maternal + paternal origin that go into the daughter cell at meiosis 1 a matter of chance?

Answer 31

since pairs lined up at random

Question 32

What is the process of the chromosomes lining up in meiosis 1 and being separated called?

Answer 32

independent segregation

Question 33

What does each member of a homologous pair of chromosomes have?

Answer 33

has exactly the same genes + so determines characteristics

Question 34

What can be different about homologous chormosomes?

Answer 34

alleles of genes

Question 35

What does the independent assortment of the homologous chromosomes do?

Answer 35

produces new genetic combinations

Question 36

How do the haploid cells fuse at fertilisation?

Answer 36

randomly

Question 37

What do the haploid cells fuse to restore at fertilisation?

Answer 37

restore diploid state

Question 38

How is variety produced in offspring from gametes?

Answer 38

each gamete has different make-up + their random fusion produces variety

Question 39

How is even more variety produced when gametes fuse?

Answer 39

gametes come from different parents two different genetic make-ups combined + so even more variety results

Question 40

What happens after the chromosomes line up alongside its homologous partner in meiosis 1?

Answer 40

chromatids of each pair become twisted around one another

Question 41

What happens during the process of chromatids of each pair becoming twisted around each other?

Answer 41

tensions created + portions of chromatids break off

Question 42

What may happen to the broken portions when chromatids of each pair become twisted around one another and tensions created + portions of chromatids break off?

Answer 42

broken portions might then re-join with chromatids of its homologous partner

Question 43

Usually, what is it during crossing over?

Answer 43

usually it's equivalent portions of homologous chromosomes that are exchanged

Question 44

What happens as the chromatids twisted, tensions created + broken portions might rejoin with chromatids of its homologous partner?

Answer 44

new genetic combinations of maternal + paternal alleles produced

Question 45

What is the process of chromatids crossing over one another many times known as?

Answer 45

crossing over

Question 46

What is the process of broken-off portions of chromatids recombining with another chromatid known as?

Answer 46

recombination

Question 47

What does crossing over increase?

Answer 47

genetic variety

Question 48

Mathematical calculation to determine number of possible combinations of chromosomes for each daughter cell?

Answer 48

2^n n- number of pairs of homologous chromosomes

Question 49

Mathematical calculation to determine number of possible combinations of chromosomes in offspring produced as result of sexual reproduction?

Answer 49

(2^n)^2 n- number of pairs of homologous chromosomes

Question 50

What are the calculations to determine number of possible combinations based on?

Answer 50

chromosomes staying intact throughout meiosis

Question 51

In practice from the calculations for number of possible combinations, what do we know?

Answer 51

crossing over between chromatids during meiosis I exchanges sections of chromosomes between homologous pairs in process called recombination as recombination occurs each time gametes made, it will greatly increase number of possible chromosome combinations in gametes