2.3: Meiosis

Question 1

Asexual reproduction

Answer 1

a single parent provides all genetic material producing offspring that is genetically identical (binary fission, mitosis etc)

Question 2

sexual reproduction

Answer 2

combines genetic material of two parents

Question 3

advantage of sexual reproduction

Answer 3

genetic diversity in offspring

Question 4

Meiosis

Answer 4

form of nuclear division that produces four haploid daughter cells from one diploid cell

Question 5

When is DNA replicated

Answer 5

prior to start of meiosis during S phase of interphase

Question 6

Reduction division

Answer 6

the process by which cells begin with two copies of each chromosome and end with only one

Question 7

prophase 1

Answer 7

1. chromosomes become visible due to supercoiling
2. replicated chromosomes from homologous pairs (tetrads/ bivalents)
3. non-sister chromatids cross over at points called chiasmata and exchange equivalent alleles
4. centrioles migrate to opposite poles and spindle fibers begin to form
5. nucleolus and nuclear membrane disintegrate

Question 8

Metaphase 1

Answer 8

1. homologous pairs move together along the metaphase plate and align in the equator
2. maternal and paternal homologues show random orientation towards the poles
3. spindle fibres attach to the centromeres of each chromosone and pull the along the equatorial metaphase plate

Question 9

Anaphase 1

Answer 9

spindle microtubules shorten and pull homologous chromosomes towards opposite poles, sister chromatids remain connected at teh centromere

Question 10

Telophase 1

Answer 10

first meiotic division ends, chromatids uncoil and the nuclear membrane reforms.

Question 11

Result of meiosis 1

Answer 11

two daughter cells with haploid nuclei (32 chromosomes, 46 chromatids)

Question 12

Prophase 2

Answer 12

1. chromosmes condense again
2. centrioles migrate to opposite poles and spindle fibers form
3. nucleolous and nuclear membrane disintegrate

Question 13

Metaphase 2

Answer 13

1. spindle fibers attach to the centromere and connect each centromere to both polls
2. spindle fibers pull chromatids to the equator

Question 14

anaphase 2

Answer 14

1. centromeres divide and chromatids are moved to opposite poles by spindle fibers
2. chromatids now called chromosomes

Question 15

Telophase 2

Answer 15

chromosomes reach opposite ends and uncoil, nuclear membrane begins to form

Question 16

result of meiosis 2

Answer 16

four haploid, genteically distint daughter cells (23 chromosomes, 23 chromatids)

Question 17

non-sister chromatids

Answer 17

posses same genes but different alleles

Question 18

crossing over

Answer 18

occurs when equivalent portions of the non-sister chromatids are exchanged between homologous chromosomes

Question 19

chiasmata

Answer 19

points at which alleles cross over

Question 20

result of crossing over

Answer 20

mew combinations of alleles that were not present in either original chromosome, contributing to genetic variation

Question 21

process of random orientation

Answer 21

1. during metaphase 1, chromosome pairs line up along metaphase plate
2. either the paternal or the maternal chromosome has equal chance of facing either pole
3. each gamete gets one copy of each chromosome and gets a random assortment of maternal or paternal versions

Question 22

number of possible chromosome combinations in gametes

Answer 22

calculated by 2^n where n is the haploid number of chromosomes

Question 23

sexual reproduction increases genteic diversity BY

Answer 23

1. crossing over of homologues in prophase 1
2. random tetrad orientation in metaphase 1
3. fusion of gametes of two undividuals

Question 24

non disjunction

Answer 24

when homologous pairs fail to separate during anaphase 1, leaving some gametes with an extra chromosme copy and some gametes without one

Question 25

correlatiin between age and trisomy

Answer 25

• positive correlation between age of mother especially and incidence of chromosomal abnormalities

Question 26

amniocentesis

Answer 26

1. method of fetal karyotyping performed between 14 and 20 weeks
2. ultrasound imagery to guide syringe or catheter, extracts fetal cells from amniotic fluid to be cultured and karyotyped
   3

Question 27

risks of amniocentesis

Answer 27

infection, fetal trauma, between 0.1% and 1% chance of miscarriage

Question 28

chronic villus sampling

Answer 28

fetal karyotyping method between 10 and 13 weeks, ultrasound imaging, fetal cells sampled by suction through vagina or abdomen, reached fetal cells in chorion

Question 29

risks of chronic villus sampling

Answer 29

bleeding, infection, 0.5%-2% chance of miscarriage

Question 30

Chorion

Answer 30

membrane surrounding fetus that develops into part of the placenta