cell division-meiosis

Question 1

meiosis starts with what kind if cell and ends with what kind of cell?

Answer 1

meiosis starts with a diploid cell and ends with four haploid gametes

Question 2

what are haploid cells?

Answer 2

cells with a single set of chromosomes

Question 3

are the cells produced in mitosis and meiosis genetically identical or different?

Answer 3

in mitosis the two diploid cells are identical, in meiosis the gametes are genetically different.

Question 4

what is a homologous chromosome?

Answer 4

a set of one maternal and paternal chromosome which pair up inside a cell during fertilisation. The genes are the same.

Question 5

how is inheritance determined?

Answer 5

in a homologous pair, the genes are the same but the alleles are different. The more dominate allele will determine the characteristic inherited.

Question 6

how are the gametes produced by meiosis genetically different (crossing-over)?

Answer 6

During prophase 1, the two chromosomes in a homologous pair come together and the chromatids of the two chromosomes cross over. The attached pair of chromosomes is called a bivalent and the points where the chromatids are joined are called the chiasmata. Parts of the chromatids break off and exchange so the maternal and paternal DNA have been exchanged- recombinate chromosomes. Exchanging of DNA means exchanging alleles which is major for genetic variation as there are new COMBINATIONS of alleles.

Question 7

meiosis involves two round of nuclear division: meiosis 1 and meiosis 2. What occurs in meiosis 1 and 2?

Answer 7

in meiosis 1, homologous chromosomes are separated from each other and in meiosis 2 sister chromatids are operated from each other.

Question 8

Before meiosis starts, interphase begins. What occurs during interphase?

Answer 8

-the cell copies the chromosomes and organelles

Question 9

Describe prophase 1 in meiosis (4 points)

Answer 9

• chromosomes condense and become visible
• homologous chromosomes link to form chiasmata and bivalents causing the exchanging of alleles
• nuclear membrane breaks down
• centrioles move to opposite poles leaving spindle fibres which start to assemble into the spindle apparatus.

Question 10

Describe metaphase 1 in meiosis (1 point)

Answer 10

-pairs of homologous chromosomes line up on the equator of the spindle apparatus

Question 11

Describe anaphase 1 in meiosis (2 points)

Answer 11

• spindle fibres shorten

- homologous chromosomes move to opposite poles causing the chiasmata to break

Question 12

where does meiosis occur?

Answer 12

occurs in diploid germ cells (reproductive cells) in the gonads (reproductive organs)

Question 13

describe telophase 1 in meiosis(4 points)

Answer 13

• chromosomes have reached the poles
• nuclear membrane reforms
• chromosomes uncoil back to their chromatin state
• cytokinesis occurs- the cells are now haploid

Question 14

Describe prophase 2 in meiosis (3 points)

Answer 14

• chromosomes condense and become visible again-sister chromatids joined at centromere
• nuclear membrane breaks down
• spindle fibres begin to develop as centrioles move to opposite poles

Question 15

Describe metaphase 2 in meiosis (1 point)

Answer 15

-chromosomes line up on the equator of the spindle apparatus

Question 16

Describe anaphase 2 in meiosis (2 points)

Answer 16

• centromere of each chromosome divides

- spindle fibres shorten and chromatids are pulled towards opposite poles

Question 17

Describe telophase 2 in meiosis

Answer 17

• chromotids reach opposite poles. They are now called chromosomes.
• nuclear membrane reforms and chromosomes uncoil back to chromatin state
• cytokinesis- two haploid cells formed

Question 18

meiosis is also known as?

Answer 18

reduction division

Question 19

what other ways in meiosis increases genetic variation (independent assortment)?

Answer 19

IN PROPHASE 1, when homologous chromosomes line up on the spindle, they are Independently assorted into their gametes which is random

Question 20

how many chromosomes do humans have?

Answer 20

46

Question 21

how do you calculate the number of genetically different gametes produced by independent assortment?

Answer 21

2 to the power of n, where n is the number of homologous pairs

Question 22

how else is genetic variation increased?

Answer 22

random fertilisation as alleles mix causing different expressions

Question 23

explain three ways in which meiosis gives rise to genetic variation (3 points)

Answer 23

• independent assortment during metaphase of chromosomes
• crossing over of alleles in a homologous chromosome pair during prophase and metaphase (chiasmata formation)
• random fertilisation

Question 24

what is a synapsis?

Answer 24

pairing of homologous chromosomes in early prophase

Question 25

why is DNA replication semi-conservative?

Answer 25

DNA replication is semi-conservative because each helix that is created contains one strand from the helix from which it was copied.

Question 26

what is discontinuous variation?

Answer 26

clear-cut alternatives of a given trait with no intermediate forms e.g blood group

Question 27

what is continuous variation?

Answer 27

a given trait that has many variations with only minor differences between them e.g height in humans

Question 28

explain the origin of continuous and discontinuous variation

Answer 28

continuous variation occurs when there is a variety of alleles but discontinuous variation occurs if the gene only has two alleles for the expression.