meiosis

Question 1

descr the prophase 1 (4)

Answer 1

1- Nuclear membrane and nucleolus start to disappear.

2- Centrosome splits and the two centrioles move apart forming spindle fibres.

3- Chromatin network condenses into individual chromosomes and pairs of
homologous chromosomes lie next to each other forming a bivalent.

4- crossing over occurs:

4.1) Inner chromatids from each homologous chromosomes overlap and touch
each other at a point called the chiasma (plural: chiasmata) in a process
called crossing over

4.2)- Chromatid segments break off and are exchanged, resulting in the exchange
of genetic material.

This process is called crossing over and it brings about variation.

Question 2

what are centrosomes

Answer 2

organelle near nucleus with 2 pairs of centrioles, when spilt, one pair of centrioles move to one pole, the other to another pole

as they move apart they form spindle fibres

Question 3

decribe crossing over (2)

Answer 3

crossing over occurs:

1) Inner chromatids from each homologous chromosomes overlap and touch
each other at a point called the chiasma (plural: chiasmata) in a process
called crossing over

2)- Chromatid segments break off and are exchanged, resulting in the exchange
of genetic material.

This process is called crossing over and it brings about variation.

Question 4

descr metaphase 1 (3)

Answer 4

1- Homologous chromosomes move to the middle of the cell (the equator) in double rows. The
two homologous chromosomes lie on opposite sides of the equator parallel to
each other

2- Which chromosome lies on which side of the equator is totally up to chance.
This is called random arrangement and brings about further variation.

3- Each chromosome in the pair becomes attached to a spindle thread by the
centromere.

Question 5

descr anaphase 1 (3)

Answer 5

1- One whole chromosome from each homologous pair is pulled to opposite poles by
contraction of the spindle fibres

2- This separates the homologous chromosomes – one to each pole. chromosomes halved in this step

3- cytokinesis (div of cytoplasm) begins

Question 6

descr telophase 1 (5)

Answer 6

1- A new nuclear membrane forms around the group
of chromosomes at each pole (chromosomes grp selves at poles )

2- Nucleolus returns.

3- spindle fibres disappear

4- Cytokinesis (division of cytoplasm) splits the
mother cell into two daughter cells.

5- Each daughter cell now has half (n) the number of chromosomes of mother cell (2n)

and each has a slightly different genetic make-up due to crossing over (2 x recombinant chromatids)

Question 7

descr prophase 2 (3)

Answer 7

1- no homologous pairs , each chromosome consists of 2 recombinant chromatids joined by centromere

2- nucleolus + nuclear membrane disappears

3- spindle forms consisting of centrioles at opp poles joined by spindle fibres

Question 8

descr metaphase 2 (2)

Answer 8

1- chromosomes
arrange themselves randomly along the equator in a single row .

2- Each chromosome becomes attached to a spindle fibre. Which chromatid faces which pole is
totally up to chance.

Question 9

descr anapahse 2 (3)

Answer 9

1- The centromere splits and the two sister chromatids sep + are pulled to opposite poles

2- these single chromatids (daughter chromosomes) form a v-shape as the centromere is pulled by the spindle fibre

3- cytokinesis begins to sep the cytoplasm

Question 10

descr telophase 2

Answer 10

1- chromatids (daughter chromosomes) grp at the pole = these called unreplicated chromosomes they are also recombinant chromatids, they have exchanged material (due to crossing over + random arrangement)

2- spindle fibres disappear

3- nuclear membrane forms around each grp of unreplicated chromosomes + a nucleus forms in each nucleus

4- cytoplasm divides n process cytokinesis

5- cytokinesis compl: 4 daughter cells - each with haploid chromosome no. + due to crossing over they are genetically diff

Question 11

the chromosome no. with a double set of chromosomes

Answer 11

diploid

Question 12

the chromosome no. with a single set of chromosomes

Answer 12

hapliod

Question 13

the complete dipliod set of chromosomes in one somatic cell of an organism, arranged in homologous pairs acc to their size, shape, and no.

it is the repre of the no., shape, and arrangements of a full set of chromosomes in the nucleus of a somatic cell

Answer 13

karyotype

Question 14

the 22 pairs of chromosomes in the human karyotype that are not associated with sex det

Answer 14

autosomes

Question 15

one pair of sex chromosomes in the human karyotype

Answer 15

gonosomes

Question 16

the time period during which a cell grows, repicates genetic material and divides

Answer 16

cell cycle

Question 17

the time period betw 2 cesecutive dividing phases during which cell growth and DNA repication occurs

Answer 17

interphase

Question 18

the process in the dividing phase during which the nucleus and chromosomes divide

Answer 18

karyokinesis “ karyo” means nucleus and “ kinesis” means synthesis for division

Question 19

the process in the dividing phase during which the cytoplasm divides

Answer 19

cytokinesis “ cyto” means cytoplasm and kinesis means synthesis for division

Question 20

the type of division that produces identical daughter cells

Answer 20

mitosis

Question 21

the type of division that occurs in the production of gametes and spores

Answer 21

meiosis

Question 22

chromatid segments (grps of genes) of homologous chromosomes break off and are exchanged

Answer 22

crossing over

Question 23

the points at which the chromatids cross over and breakages occur

Answer 23

chiasmata

Question 24

phase of meiosis during which the chromosome no. halves

Answer 24

anaphase 1

Question 25

phase of meiosis during which four hapliod daughter cells are formed

Answer 25

telophase 2

Question 26

the diff betw oranisms of a species due to diff gene combinations

Answer 26

genetic variations

Question 27

chromosme abnormalities caused by chnages in the chromosome no. when meiosis does not proceed normally

Answer 27

chromosome mutation

Question 28

a condition that sometimes occurs when there are extra or missing chromosomes in a cell

Answer 28

aneuploidy

Question 29

a chromosome abnormality known as Trisomy 21 where an indiv has 47 chromosomes in each somatic cell

Answer 29

down syndrome

Question 30

a condition where more than 2 sets of chromosomes occur in a cell

Answer 30

polyploidy

Question 31

why is “crossing over imp”

Answer 31

1- Crossing over brings about an exchange of genetic material during the process of
gamete formation which results in the formation of new genetic combinations.

2- This results in formation of gametes that will give rise to individuals that are
genetically different from their parents and siblings.

Question 32

what is the purpose of meiosis/ reduction division

Answer 32

1- formation of gametes (sec cells) in the sex organs of animals (gametogenis)

Question 33

what is the process of gamete formation known as

Answer 33

gametogenesis

Question 34

what is the process called when sperms form in the testes

Answer 34

spermatogenesis

Question 35

what is the process called when ova/ eggs are formed in the varied

Answer 35

oogensis

Question 36

name 3 importance of meiosis

Answer 36

1- hapliod gametes/spores production

2- halving chromosome no. in meisosis (reduction div) overcomes the doubling effect of fertilisation + maintains a constant chromosome no. in each gen

3- genetic variation: 1- crossing over, 2- random arrangement of chromosomes on the equator

Question 37

what are the 2 types of gametogenesis

Answer 37

1- spermatogenesis (sperm in testes)
2- oogenesis (ova formed in ovaries )

Question 38

what are the 3 sources of variation in gametes and spores

Answer 38

1- crossing over: of chromatids, the exchange of genetic material during prophase 1 , reshuffling/ recombination of diff genetic material

2- random arrangement of chromosomes: on the equator in metaphase 1 and 2 , maternal + paternal chromosomes lie randomly on equator bef sep to form part of new combination

3- random fertilisation= possibility of which sperm fuses with which egg in fertilisation

Question 39

name 5 diff betw meiosis 1 and meiosis 2

Answer 39

1- meiosis 1: Chromosomes arrange at the equator of
the cell in homologous pairs
meiosis 2: Chromosomes line up at the equator of
the cell individually

2- meiosis 1: Whole chromosomes move to opposite
poles of the cel
meiosis 2: Chromatids move to opposite poles of
the cell

3- meiosis 1: Two cells are formed at the end of this
division
meiosis 2: Four cells are formed at the end of this
division

4- meiosis 1: The chromosome number is halved
during meiosis I (diploid → haploid)
meiosis 2: The chromosome number remains the
same (haploid) during meiosis II

5- meiosis 1: Crossing over takes place
meiosis 2: Crossing over does not take place

Question 40

name 8 differences between mitosis and meiosis

Answer 40

1- mitosis: occurs in body cells (somatic cells)
meiosis: occurs in sex organs

2- mitosis: Two daughter cells are formed
meiosis: Four daughter cells are formed

3- mitosis: Daughter cells are genetically identical to
one another and to the parent cell
meiosis: Daughter cells are genetically different
from each other and from the parent cell

4-mitosis: 1 division
meiosis: 2 divisions

5- mitosis: no crossing over
meiosis: crossing over occurs

6- mitosis: centrosomes divide during anaphase
meiosis: centrosomes divide only anaphase 2 not anaphase 1

7- mitosis: chromosome number remains the same
meiosis: chromosome number is halved

8- mitosis: no bivalent formed ( no pairings of homologous chromosomes
meiosis: bivalent formed ( homologous chromosomes arrange themselves in pairs, bivalent forms during prophase 1 when the are in contact with each other