3.3 MEIOSIS Flashcards Preview

Biology > 3.3 MEIOSIS > Flashcards

Flashcards in 3.3 MEIOSIS Deck (33)
Loading flashcards...
1
Q

G1 PHASE

A

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

2
Q

S PHASE

A

DNA replication

3
Q

G2 PHASE

A

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

4
Q

PROPHASE I (6)

A

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

5
Q

METAPHASE I

A

Bivalents line up at the equator

Random Orientation occurs

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

6
Q

RANDOM ORIENTATION

METAPHASE I

A

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.

7
Q

ANAPHASE I

A

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.

8
Q

TELOPHASE I

A

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.

9
Q

PROPHASE II

A

Chromosomes condense again and become visible.

Spindle fibers again form.

Nuclear membrane disintegrates again.

10
Q

METAPHASE II

A

Chromosomes line up along the equator.

Spindle fibre attaches to the centromere of the chromosome.

11
Q

ANAPHASE II

A

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

12
Q

TELOPHASE II

A

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

13
Q

GENETIC VARIATION IS DUE TO

A

crossing over in prophase I

14
Q

CROSSING OVER

A

Prophase I of meiosis.

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

15
Q

CROSSING OVER OCCURS BETWEEN…

A

non-sister chromatids of a particular chromosome.

16
Q

CHIASMATA

A

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

17
Q

CROSSING OVER PRODUCT

A

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

18
Q

CROSSING OVER CONSEQUENCE

A

This creates variation in the offspring regardless of random orientation.

19
Q

WHEN DOES RANDOM ORIENTATION OCCUR?

A

Occurs in metaphase I of meiosis.

20
Q

RANDOM ORIENTATION CONSEQUENCE

A

the genetic variation possibilities in the offspring is immeasurable.

21
Q

NUMBER OF COMBINATIONS DUE TO RANDOM ORIENTATION

A

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

22
Q

NUMBER OF COMBINATIONS DUE TO RANDOM ORIENTATION

A

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

23
Q

NON- DISJUNCTION

A

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

24
Q

WHEN CAN NON- DISJUNCTION OCCUR

A

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.

25
Q

NON- DISJUNCTION CONSEQUENCE

A

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

26
Q

NON- DISJUNCTION EXAMPLE

A

Down’s syndrome

27
Q

DOWN SYNDROME

A

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.

28
Q

DOWN SYNDROME AKA

A

Trisomy 21.

29
Q

DOWN SYNDROME SYMPTOMS

A

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

30
Q

KARYOGRAM

A

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

31
Q

USE OF KARYOGRAM

A

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

32
Q

AMNIOCENTESIS

A

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

33
Q

KARYOGRAM AND AMNIOCENTESIS

A

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