meiosis

Question 1

what is a centromere

Answer 1

the structure that holds two chromatids together

Question 2

what is a homologous pair

Answer 2

two corresponding chromosomes with the same structure that carry genes for the same hereditary traits

Question 3

what is a haploid

Answer 3

nucleus containing half set of chromosomes( usually in gametes which has undergone meiosis)

Question 4

what is a diploid

Answer 4

nucleus containing full set of chromosomes

Question 5

what is gametogenesis

Answer 5

the process in which cells undergo meiosis to form gametes

Question 6

what are chromosomes

Answer 6

chromosomes are long thread-like structures that form part of the chromatin network in the nuclei of the cells

Question 7

in which cell is the number of chromosomes in each cell the same.

Answer 7

Somatic cells

Question 8

what are chromosomes made up of

Answer 8

they are made up of two sets, one set from the mother and the other from the father they are therefore diploid cells

Question 9

how is homologous pairs formed

Answer 9

For each paternal chromosome, there is a matching maternal chromosome forming homologous pairs. the chromosomes pairing are the same size and shape and have the same genes in the same place however the alleles for each trait may not be the same

Question 10

what takes place in the interphase of the cell

Answer 10

the DNA of each chromosome replicates to form two identical threads of chromatids joined by a centromere.

Question 11

what is meiosis

Answer 11

( also known as reduction division) it is a special type of cell division that results in four daughter cells each with half the genetic material of the parent cell// the type of cell division responsible for having the genetic make-up of a cell to form a haploid cell( gamete).

Question 12

where does meiosis take place

Answer 12

in the reproductive organs of both plants and animals in order to produce gametes

Question 13

what happens to the chromosome number during meiosis

Answer 13

the number is reduced from two sets(2N) in the parent cell to one set (N) in each of the daughter cells

Question 14

how do you form a diploid zygote

Answer 14

during sexual reproduction a male and female haploid gamete fuse during fertilisation

Question 15

where does meiosis take place for plants specifically

Answer 15

for males, it is the microsporangia which are the pollen sacs in the male anthers.
And for females, it happens in the megasporangia, which are the ovules in the female ovaries

Question 16

where does meiosis take place for animals specifically

Answer 16

for males, the formation of sperm in the testis is known as spermatogenesis.
And for females, the formation of egg cells in the ovaries is called oogenesis.

Question 17

what is the process of meiosis

Answer 17

DNA of the parent cells is replicated during interphase which occurs before mitosis and meiosis.
In meiosis, replication is followed by two divisions :

meiosis1- reduction division which results in two cells being formed each with half the number of chromosomes( haploid).

meiosis2- copying division which involves the two haploid cells each dividing again by mitosis to form four haploid cells.

Question 18

what first happens in meiosis 1 prophase 1

Answer 18

1. a structure known as the spindle starts to form, the spindle has two poles on opposite ends of the cell and spindle fibres that connect the poles.
2. the chromosomes condense and become visible as individual chromosomes
3. homologous chromosomes arrange themselves along their lengths, aligned according to genes, in a process called synapsis.
4. crossing over occurs during prophase 1, segments of the chromosomes and genes are exchanged between the two chromosomes of a homologous pair.

Question 19

what happens during meiosis 1 metaphase 1.

Answer 19

1. the pairs of homologous chromosomes(bivalents) arrange themselves along the centre of the cell, known as the equator.
2. one chromosome of each pair faces each of the two poles. The chromosomes attach to the spindle threads

Question 20

what happens during meiosis 1 anaphase 1

Answer 20

1. the spindle threads pull the homologs apart
2. the chromosomes move towards separate poles of the spindle
3. one chromosome of each homologous pair is pulled to the opposite pole.

Question 21

what happens during meiosis 1 telophase 1

Answer 21

1. each half of the cell now has a haploid number of chromosomes
2. cytokinesis takes place which is the division of the cell into two parts
3. the nuclear membrane starts to form again in both of the new cells
4. there are now two daughter cells, each with a haploid number of chromosomes.

Question 22

what happens in meiosis 2

Answer 22

this is copying division which involves the two haploid cells dividing again by mitosis to form 4 haploid cells

Question 23

what is crossing over

Answer 23

it is the mutual exchange of pieces of the chromosomes so that whole groups of genes are swapped between maternal and paternal chromosomes, this occurs during prophase 1.

Question 24

what happens during crossing over

Answer 24

replicated homologous pairs of chromosomes come together during synapsis to form bivalents. they swap pieces of their inner chromatids by breaking and reforming the DNA while paired up. the point of crossing over where chromatids break is called chiasmata.
some genes from maternal chromatids change place with paternal chromatids, forming a recombinant chromatid. outer unchanged chromatids are called parentals.

Question 25

why is crossing over important

Answer 25

the exchange of genetic material produces chromatids with a unique combination of genes. this increases variation among daughter cells. this is why siblings do not look 100% the same except for identical twins.