meiosis

Question 1

haploid (n)

Answer 1

• one complete set of chromosomes in a cell (n=23)

Question 2

diploid(2n)

Answer 2

• two complete sets of chromosomes in a cell (2n=46)

Question 3

sex cells (gametes)

Answer 3

specialized cells called gametes (sperm cells and egg cells).
they have a haploid number of chromosomes and are produced through meiosis

Question 4

somatic cells(body cells)

Answer 4

any cells in an organism excluding male and female gametes .they are diploid and are produced through mitosis

Question 5

gonosomes

Answer 5

sex chromosomes(XX or XY)

Question 6

autosomes

Answer 6

the first 22 pairs of chromosomes which control the appearance ,structure and functionings of the body

Question 7

similarities between mitosis and meiosis

Answer 7

• phases are the same

Question 8

differences between meiosis and mitosis

Answer 8

meiosis
- occurs in sex organs
- 4 daughter cells formed
- crossing over occurs
- karyokinesis and cytokinesis occurs

mitosis
- occurs in body cells
- karyokinesis and cytokinesis occurs once
- 2 daughter cells formed
- crossing over does not occur

Question 9

definition of meiosis

Answer 9

type of cell division used to produce gametes or sex cells

Question 10

site of meiosis in plants and animals

Answer 10

animals
- occurs in the sex organs (ovaries and testes ) to produce gametes

plants
- mosses and spores produce spores used for reproduction
- in flowering plants it takes place in the anther and in the ovule

Question 11

events of interphase

Answer 11

• DNA replication takes place
• chromosomes which are single threads become double
• each chromosomes will now consist of two chromatids joined by a centromere
• DNA replication helps to double the genetic material so that it can be shared by the new cells arising from cell division

Question 12

what is down syndrome caused by

Answer 12

it is caused by a non disjunction of chromosomes which results in the presence of an extra chromosome number 21

Question 12

importance of meiosis

Answer 12

• production of haploid gametes
• the halving effect of meiosis overcomes the doubling effect of fertilization thus maintaining a constant chromosome number from one generation to the next
• mechanism to introduce genetic variation through crossing over and the random arrangement of chromosomes at the equator

Question 13

where does down syndrome occur in meiosis

Answer 13

in anaphase 1 and anaphase 2

Question 14

what leads to down syndrome

Answer 14

• if there is non disjunction of chromosome pair 21 in humans , it leads to the formation of an abnormal gamete with an extra copy of chromosome 21
• if there is fusion between a normal gamete (with 23 chromosomes) and an abnormal gamete (with an extra copy of chromosome 21 ) ,it leads to down syndrome

Question 15

prophase 1

Answer 15

• nuclear membrane and nucleolus disappears
• centrosome splits and the two centrioles move apart forming spindle fibers
• pairs of homologous chromosomes lie next to each other forming a bivalent
• crossing over occurs .chromatids from each homologous chromosome overlap and touch each other at the chiasma
• chromatid segments break off and are exchanged resulting in the exchange of genetic material

Question 16

metaphase 1

Answer 16

• homologous chromosomes move to the equator
• they lie on opposite sides of the equator parallel to each other
• this called random arrangement and brings about further variation
• each chromosome in the homologous pair becomes attached to a spindle fiber

Question 17

anaphase 1

Answer 17

• one chromosome from each pair is pulled to opposite poles by contraction of the spindle fibers
• this separates the homologous chromosomes ,one to each pole

Question 18

telophase 1

Answer 18

• a nuclear membrane and nucleolus forms
• cytokinesis (division of cytoplasm ) splits the mother cell into two daughter cells

Question 19

prophase 2

Answer 19

• nuclear membrane and nucleolus disappears
• centrosome splits into 2 centrioles and a spindle fiber forms

Question 20

metaphase 2

Answer 20

single chromosomes arrange themselves randomly along the equator
- each chromosome becomes attached to a spindle fiber

Question 21

anaphase 2

Answer 21

• centromere splits separating each chromosome into 2 daughter chromosome each pulled to opposite poles

Question 22

telophase 2

Answer 22

• a new nuclear membrane forms
• cytokinesis splits the cells into 2 new cells
• there will now be 4 daughter cells
• these cells will be haploid and genetically different