4: GENETICS - MEIOSIS

Question 1

What is the diploid no. of chromosomes?

Answer 1

2n

Question 2

What is the haploid no. of chromosomes?

Answer 2

n

Question 3

What is the diploid no. of chromosomes in humans?

Answer 3

46

Question 4

What is the haploid no. of chromosomes in humans?

Answer 4

23

Question 5

What is a gamete?

Answer 5

• sperm cells in males
• egg cells in females

Question 6

Do gametes have the diploid (2n)/haploid (n) no. of chromosomes?

Answer 6

haploid no. (n)

Question 7

What is the name of the process whereby a haploid cells are formed from a diploid cell?

Answer 7

meiosis

Question 8

How does fertilisation result in the production of a cell with the diploid no. of chromosomes?

Answer 8

a haploid sperm fuses with a haploid egg so the cell formed has the diploid no. of chromosomes

Question 9

What is the name of the cell produced from fertilisation?

Answer 9

zygote

Question 10

Describe the process of meiosis

Answer 10

• DNA unravels and replicates so there’s 2 copies of each chromosome
• DNA condenses to form double armed chromosomes each made up of 2 sister chromatids joined by a centromere
• MEIOSIS I - chromosomes arrange themselves into homologous pairs. homologous pairs are then separated by spindle fibres, halving the chromosome no. (crossing over and independent segregation also occur in meiosis I)
• MEIOSIS II - pairs of sister chromatids that make up each chromosome are separated (centromere is divided and the chromatids are pulled to opposite poles of the cell by spindle fibres)
• 4 genetically varied haploid cells are produced

Question 11

What 2 events in meiosis lead to genetic variation?

Answer 11

• crossing over
• independent segregation

Question 12

What is crossing over?

Answer 12

crossing over occurs between chromatids, whereby they form a chiasmata (twist around each other) and equal lengths of the chromatids including the same genes swap over

Question 13

How does crossing over lead to genetic variation?

Answer 13

different combination of alleles

Question 14

What is independent segregation?

Answer 14

• ‘Shuffling’ of maternal and paternal chromosomes ​
• during Meiosis I, homologous pairs are randomly assorted to the daughter cells so each of the 4 daughter cells have different combinations of maternal and paternal chromosomes

Question 15

What are the differences between the outcomes of meiosis and mitosis?

Answer 15

• mitosis produces cells with same no. of chromosomes as the parent cell whereas meiosis produces cells with half the no. of chromosomes as the parent cell
• daughter cells produced by mitosis are genetically identical to each other and the parent cell whereas daughter cells produced by meiosis are genetically different from each other and the parent cell
• mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells