Meisosis

Question 1

Purpose of Meiosis

Answer 1

In animals, meiosis forms gametes. Diploid (2n) cells become haploid gametes (n). The gametes nuclei can then fuse to form a diploid zygote (2n) of the next generation.

In plants, meiosis forms spores. Diploid (2n) cells become haploid spores (n) which grow into gametophytes (n) which produce gametes (n). Haploid gametes (n) can then fuse to form a diploid zygote (2n) of the next generation (Plant life cycles in covered in Grade 11)

Thus meiosis maintains the correct chromosome number to enable sexual reproduction to occur.

Sexual reproduction allows for gametes with different gene combinations which leads to genetic variation in populations.

Question 2

Genetic variation

Answer 2

Crossing over: crossing over during Prophase 1

Random arrangement of chromosones on the equator: the random arrangement (positioning) of chromosomes on the equator during metaphase of meiosis

Random fertilisation: the fact that random gametes will end up fertilising each other when individuals breed

Random mate selection for sexual reproduction

Question 3

Non-Disjunction

Answer 3

A non-disjunction is the failure of chromosomes to separate normally during meiosis

Question 4

Aneuploidy

Answer 4

If fertilisation subsequently occurs, this results in a new chromosome number for the individual, called aneuploidy.

Question 5

Polyploidy

Answer 5

When the number of chromosomes changes in an organism due to a total non-disjunction, the result is more than two sets of chromosomes in a cell. This is called polyploidy

Question 6

Down syndrome

Answer 6

Down’s Syndrome is caused by the non-disjunction of chromosomes which results in the presence of an extra chromosome number 21 (referred to as trisomy-21)

Question 7

Amniocentesis

Answer 7

process by which amniotic fluid is removed so that the karyotype of foetal cells in the amniotic fluid can be analysed