meiosis and variation

Question 1

Meiosis

Answer 1

cell division that reduces the chromosome number by half, producing genetically different cells

Question 2

homologous chromosomes

Answer 2

pair of chromosomes, one from each parent, with genes for the same traits

Question 3

bivalents

Answer 3

paired homologous chromosomes during prophase 1

Question 4

chiasmata

Answer 4

points where crossing over occurs

Question 5

haploid

Answer 5

• n
• single set of chromosomes

Question 6

diploid

Answer 6

2n
two sets of chromosomes

Question 7

what is the function of meiosis

Answer 7

produce gametes

Question 8

two rounds of division in meiosis

Answer 8

meiosis I
meiosis II

Question 9

purpose of meiosis 1

Answer 9

separate the homologous chromosomes, reducing the chromosome number by half

Question 10

what happens before meiosis 1

Answer 10

the 2 sets of chromosomes in the nucleus replicate during interphase

Question 11

prophase 1

Answer 11

• chromosomes condense as bivalents
• crossing over occurs at the chiasmata
• spindle fibres form, and nuclear membrane disintegrates

Question 12

metaphase 1

Answer 12

• homologous pairs align along the equator of the cell
• random orientation of homologous pairs introduces an independent assortment

Question 13

anaphase 1

Answer 13

• homologous chromosomes are pulled to opposite poles by spindle fibres
• sister chromatids remain attached at the centromeres

Question 14

telophase 1 and cytokinesis

Answer 14

• nuclear membranes reform around two haploid sets
• cell divides into 2 haploid cells

Question 15

meiosis II purpose

Answer 15

separates sister chromatids to produce four haploid cells

Question 16

prophase II

Answer 16

• chromosomes condense again
• spindle fibres form in each haploid cell

Question 17

metaphase II

Answer 17

• chromosomes align at the equator
• sister chromatids are oriented towards opposite poles

Question 18

anaphase II

Answer 18

sister chromatids are separated and pulled to opposite poles

Question 19

telophase II and cytokinesis

Answer 19

• nuclear membrane reforms around the chromosomes in each four cells
• cytoplasm divides
• produces 4 genetically unique haploid cells

Question 20

how can variation happen in meiosis

Answer 20

• crossing over in prophase I
• independent assortment in metaphase 1
• mutation

Question 21

cetromere

Answer 21

site of attachment of spindle fibers

Question 22

Explain how meiosis can lead to variation (5marks)

Answer 22

1. During prophase 1 of meiosis, homolohous chromosomes pair up and exchange genetic material at points called chiasmata. This is known as crossing over, resulting in new combination of alleles on the chromatids, increasing variation among offspring.

2.
In metaphase I, homologous chromosomes line up randomly along the equator of the cell. This random allignement means that different combinations of maternal and paternal chromosomes can be inherited, leading to g enetic variation in the gametes.

Question 23

what is the significance of meiosis

Answer 23

• offers a mechanism for some genetic stability.
• meiosis leads to genetic variation.

Question 24

meiosis vs. mitosis: similarities

Answer 24

• replication of the DNA in interphase
• replication of cell organelles
• similar stages of PMAT
• formation of a spindle

Question 25

differences of mitosis and meiosis

Answer 25

• mitosis consists of one division, and meiosis has 2
• mitosis involves the separation of sister chromatids, meiosis is the separation of homologous chromosomes+ separation of chromatids
• no crossing over occurs in mitosis
• no chiasmata is formed in mitosis
• daughter nuclei have same number of chromosomes as parent nucleus in mitosis, meiosis is half
• no genetic variation in daughter nuclei in mitosis