Mitosis and Meiosis

Question 1

Explain the stages of mitosis

Answer 1

Prophase -The chromosomes condense getting shorten and fatter
Telophase- The chromes line up along the middle of the cell and become attached to the spindle by their centromere
Anaphase- The centimetre divides, separating each pair of sister chromatids
Telophase- The chromatids reach opposite poles on the spindles. They uncoil and become long and thin. A nuclear membrane forms round each group

Question 2

Explain the stages of meiosis

Answer 2

Interphase - The cell copies the chromosomes and organelles. However the chromosomes are not visible as distinct structures
MEIOSIS 1:
Prophase 1 - The chromosomes condense and become visible. The homologues chromosomes link together forming chiasmata. Crossing over will then take place and the nuclear membrane will break down, and centrioles move to opposite poles and spindles fibres will start to assemble into the the spindles apparatus
Metaphase 1 - The pairs of homologous chromosomes now line up on the equator of the spindles apparatus
Anaphase 1 - The spindles fibres shorten and the homologous chromosomes move towards opposite poles This happens because the chiasmata between homologous chromosomes break
Telophase 1- The chromosomes reach the poles of the cell, the nucleus membrane reforms and. chromosome uncoil bak to their chromatin state
Cytokinesis - The cell membrane forms, causing the cells to divide into two cells. Which are haploid
MEIOIS 2:
Prophase 2 - Chromomse condense and become visible again. Nucleus membrane breaks down and spindles fibres begin to develop
Metaphase 2 - The chromosomes line up on the equator of the spindles apparatus
Anaphase 2 - The centimetre of each chromosomes divide and the spindles fibres shorten. The chromatids are now pulled towards opposite poles of the cell
Telophase 2 - The nucleus membrane reforms and the chromosomes now uncoil back to their cremation state.
Cytokinesis -Cell membrane forms, causing the cell to divide into two cells. Which are haploid cells
Meiosis start with a diploid cell and produces four haploid cell. Each gamete made is genetically different

Question 3

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Question 4

What is crossing over

Answer 4

Exchange of the material between chromatids, produces different cobination of alleles

Question 5

What is the chiasma (Plural chiasmata)

Answer 5

It is the point where chromatids break

Question 6

Describe and explain the processes that occur during meiosis that increase genetic variation.

Answer 6

Homologous chromosomes pair up.
-Independent assortment/segregation occurs
-Maternal and paternal chromosomes are re-shuffled in any combination.
-Crossing over leads to exchange of parts of (non-sister) chromatids / alleles between homologous chromosomes; - (Both) create new combinations of alleles;

Question 7

Explain how the chromosome number is halved during meiosis.

Answer 7

-Homologous chromosomes pair up
-One of each pair goes to each (daughter) cell / to opposite poles;

Question 8

Linked genes are those that are

Answer 8

-On the same chromosome
-Close together

Question 9

What is linkage

Answer 9

This is when genes are inherited together, so will tend to be passed as a pair to the same gamete

Question 10

What ratio shows the genes are inherited together

Answer 10

A 3:1 ratio shows the genes are inherited together

Question 11

What does inherited independently mean

Answer 12

If two genes are on the same chromosome and are very close together, that means they always end up together and so are inherited together

Question 13

In Australia 8% of males are colour blind compared to 0.4% of females. Explain why colour blindness if more common in males than females

Answer 13

Colour blindness is caused by a recessive allele on the X Chromosome. Males are XY
Males only need to inherit one recessive allele to be colour blind. Females would need to inherit 2 recessive alleles which is less probable

Question 14

Describe and explain how, in mammals, events following the acrosome reaction prevent more than one sperm fertilising an egg.(4)

Answer 14

-Sperm cell membrane and egg cell fuse
-This causes the cortical granules to move towards the cell membrane
-The process of exocytosis occurs and releases its contents into the jelly layer
-Which causes it to harden zone pellucida
-A change in the charge across the egg cell membrane occurs

Question 15

Animals produce haploid gametes by meiosis.
Explain how meiosis gives rise to genetic variation in gametes.(2)

Answer 15

-Independent assortment gives rise to new combinations of maternal and paternal chromosomes
-Crossing over involves the swapping of sections of chromatids

Question 16

What does polygenic mean

Answer 16

a characteristic showing continuous variation (1)
* caused by multiple genes at different loci