3.3 MEIOSIS

Question 1

G1 PHASE

Answer 1

increase cytoplasm volume, organelle production and protein synthesis (normal growth)

Question 2

S PHASE

Answer 2

DNA replication

Question 3

G2 PHASE

Answer 3

Increase cytoplasm volume, double the amount of organelle and protein synthesis (prepare for cell division)

Question 4

PROPHASE I (6)

Answer 4

DNA supercoils and condenses. Chromosomes are visible under light microscope.

Nuclear membrane begins to break down and disintegrate.

The homologous chromosomes associate with each other to form
bivalenT.

Crossing over occurs: non-sister chromatids exchange genetic
information.

The crossing over point is called chiasma

Spindle fiber begins to form

Question 5

METAPHASE I

Answer 5

Bivalents line up at the equator

Random Orientation occurs

Spindle fibers (microtubules) from each of the centrosomes attach to the centromere of bivalents.

Question 6

RANDOM ORIENTATION

METAPHASE I

Answer 6

bivalents (homologous pairs) that come from the
mother or the father line up randomly on either side of the cell equator, independently of the other homologous pairs. Hence the daughter nuclei get a different mix of chromosomes.

Question 7

ANAPHASE I

Answer 7

Contraction of the spindle fibers pulls homologous chromosome pair apart.

Chiasmata breaks apart and separate.

One chromosome of each pair move to opposite poles of the cell.

Question 8

TELOPHASE I

Answer 8

Chromosome begins to uncoil and nuclear envelop reforms.

Chromosome number reduces from 2n (diploid) to n (haploid); however each
chromatid still has the replicated sister chromatid still attached (not homologous
pairs anymore).

Cytokinesis occurs and the cell splits into two separate cells.

Question 9

PROPHASE II

Answer 9

Chromosomes condense again and become visible.

Spindle fibers again form.

Nuclear membrane disintegrates again.

Question 10

METAPHASE II

Answer 10

Chromosomes line up along the equator.

Spindle fibre attaches to the centromere of the chromosome.

Question 11

ANAPHASE II

Answer 11

Spindle fibers pull apart the centromeres and sister chromatids are pulled towards the opposite poles.

Question 12

TELOPHASE II

Answer 12

Chromosomes arrive at opposite poles.

Nuclear envelope begins to develop around each of the four haploid cells.

Chromosomes begin to unwind to form chromatin.

Cytokinesis occurs and cells are split apart

Question 13

GENETIC VARIATION IS DUE TO

Answer 13

crossing over in prophase I

Question 14

CROSSING OVER

Answer 14

Prophase I of meiosis.

Crossing over creates new combinations of linked genes (genes on the same chromosome) from the mother and the father.

Question 15

CROSSING OVER OCCURS BETWEEN…

Answer 15

non-sister chromatids of a particular chromosome.

Question 16

CHIASMATA

Answer 16

Chiasmata are points where two homologous non-sister chromatids exchange genetic material during crossing over in meiosis

Question 17

CROSSING OVER PRODUCT

Answer 17

When the chromatids are separated into different gametes after anaphase II, the gametes produced will not contain the same combination of alleles as
the parental chromosomes

Question 18

CROSSING OVER CONSEQUENCE

Answer 18

This creates variation in the offspring regardless of random orientation.

Question 19

WHEN DOES RANDOM ORIENTATION OCCUR?

Answer 19

Occurs in metaphase I of meiosis.

Question 20

RANDOM ORIENTATION CONSEQUENCE

Answer 20

the genetic variation possibilities in the offspring is immeasurable.

Question 21

NUMBER OF COMBINATIONS DUE TO RANDOM ORIENTATION

Answer 21

the number of combinations that can occur in the gamete is 2 to the power of n (n=number of chromosome pairs).

Question 22

NUMBER OF COMBINATIONS DUE TO RANDOM ORIENTATION

Answer 22

the number of combinations that can occur in the gamete is 2 to the power of n (n=number of chromosome pairs).

Question 23

NON- DISJUNCTION

Answer 23

an error in meiosis, where the chromosome pairs fail to split during cell division.

Question 24

WHEN CAN NON- DISJUNCTION OCCUR

Answer 24

Non-disjunction can occur in anaphase I where the homologous pairs fail to split, or it can occur in anaphase II, where the sister chromatids fail to split.

Question 25

NON- DISJUNCTION CONSEQUENCE

Answer 25

Too many chromosomes in a gamete cell or too few chromosomes in the final gamete cell.

Question 26

NON- DISJUNCTION EXAMPLE

Answer 26

Down’s syndrome

Question 27

DOWN SYNDROME

Answer 27

occurs when chromosome 21 fails to separate,
and one of the gametes ends up with an extra chromosome 21.

Therefore, a child that receives that gamete with an extra chromosome 21 will have 47 chromosomes in every cell.

Question 28

DOWN SYNDROME AKA

Answer 28

Trisomy 21.

Question 29

DOWN SYNDROME SYMPTOMS

Answer 29

Impairment in cognitive ability and physical growth, hearing loss, oversized tongue, shorter limbs and social
difficulties.

Question 30

KARYOGRAM

Answer 30

A diagram or photograph of the chromosomes present in a nucleus arranged in homologous pairs of descending length.

Question 31

USE OF KARYOGRAM

Answer 31

to make diagnosis of non-disjunction genetic disorder, such as Down’s Syndrome

Question 32

AMNIOCENTESIS

Answer 32

a sample of the amniotic fluid surrounding the baby is removed using a syringe.

Question 33

KARYOGRAM AND AMNIOCENTESIS

Answer 33

The sample contains skin cell from the baby, so we can use that to make a karyogram, in order to check for genetic disorder.