Meiosis And Genetic Variation

Question 1

What are normal body cells diploid number?

Answer 1

2N of chromosomes- meaning each cell contains two of each chromosome and one from the mum and one from the dad

Question 2

What is a haploid number of chromosomes?

Answer 2

Gam’s number of chromosomes - n

Question 3

Explain the process of meiosis

Answer 3

1- dna unravels and replicates producing two copies of chromosomes called chromatids
2- dna condenses forming double armed chromosomes (sister chromosomes) that are joined in the middle of the centromere
3- meiosis 1- chromosomes arranged in homologous pairs
4- homologous pairs are separated halving chromosome number
5- meiosis 2- sister chromatids separated
6- 4 haploid cells that are genetically different are produced

Question 4

How do chromatids crossover in meiosis one?

Answer 4

Homologous pairs of chromosomes come together and pair up
- The chromatids twist around each other and bits of chromatids swap over
- The cremated still contain the same genes but now have a different combination of all

Question 5

How does crossing over lead to genetic variation?

Answer 5

• One chromosome from each homologous pair ends up in each cell
• Each cell has a different chromatid and therefore a different set of alleles which increases genetic variation

Question 6

How does independent segregation of chromosomes lead to genetic variation?

Answer 6

1- each homologous pair of chromosomes in your cells is made up of one chromosome from each mum and one chromosome from each dad
- When the homologous pairs are separated in meiosis one it’s completely random in which chromosome from each pair ends up in each daughter cell
- so the four of cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
- This is called independent segregation
- This shuffling of chromosomes leads to genetic variation in any potential offsprings

Question 7

Differences between mitosis and meiosis

Answer 7

Mitosis-
- Produce the cell cells with the same number of chromosomes as the parent
- dayghter Cells are genetically identical
- Producers, two daughter
cells

Meiosis-
- Producers cells with half the number of chromosomes as the parent cell
- Daughter cells are genetically different from one another and the parent cell
- produces four daughter cells 

Question 8

What causes down syndrome?

Answer 8

• A person having an extra copy of chromosome 21
• Nondisjunction means that chromosome 21 fails to separate properly during meiosis so the cell gets an extra copy of 21 and another gets none
• When the game meet with the extra copy fuses another gamete at fertilisation the resulting zygote will have three copies of chromosome 21