mitosis and meisosis

Question 1

meiosis

Answer 1

• special type of cell division used solely to produce gametes – oocytes and sperm.
• occurs in the gonads (ovaries and testis).
• is required to produce gametes that are haploid, to allow fertilisation and production of a diploid zygote, resulting in genetic variation within the gene pool.

Meiosis can be broken down into two major stages (Meiosis I and Meiosis II), each with their own prophase, metaphase, anaphase, and telophase stages.

Question 2

meiosis I

Answer 2

a reduction division

homologous chromosomes are separated, thus reducing the number from diploid to haploid.

Question 3

meiosis I - prophase I

Answer 3

• chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

Question 4

meiosis I- metaphase I

Answer 4

centromeres and allign them along the middle of cell

Question 5

meiosis I- anaphase I

Answer 5

spindle fibres contract and split the bivalent

Question 6

meiosis I- telophase I

Answer 6

chromosomes decondense, nucleus may reform and the cell undergoes cytokinesis to form two haploid cells

Question 7

meiosis II- prophase II

Answer 7

• chromosomes condense, nuclear membrane dissolves and centrosomes move to opposite poles

Question 8

meiosis II- metaphase II

Answer 8

spindle fibres from opposing centrosomes attach to chromosomes at the centromere and align them along the cell equator

Question 9

meiosis II- anaphase II

Answer 9

spindle fibres contract and separate the sister chromatids
chromatids are now called chromosomes, and are moved to opposite poles

Question 10

meiosis II- telophase II

Answer 10

chromosomes decondense, nuclear membrane reforms, cells divide to form four haploid daughter cells in total

Question 11

crossing over and random assortment in prophase

Answer 11

During prophase-I, crossing over occurs. This is vital for producing variation in the genetic pool.

The homologous pairs of chromosomes line up in register, matching the location) of the corresponding genes together.

As the chromosomes condense, crossing over sites are formed (between the maternal and paternal chromosomes) and random exchange of genetic material occurs between the homologous chromosomes.

Question 12

crossing over and random assortment in metaphase

Answer 12

During metaphase-I, the homologous chromosomes align as pairs in a random order (a mixture of maternal and paternal arrangement).

This ensures a subsequent reshuffling of the maternal and paternal chromosomes and prevents the segregation of all maternal chromosomes into one cell and paternal into another.