Diversity, Classification And Variation

Question 1

What are gametes?

Answer 1

They are the sex organs in humans

Question 2

How is a zygote formed?

Answer 2

When gametes join together during fertilisation

Question 3

What type of number of chromosomes do body cells have?

Answer 3

-have a diploid number (2n)

• contains two of each chromosomes

Question 4

What type of number of chromosomes do gametes have?

Answer 4

-haploid (n) number of chromosomes

-one copy of each chromosome

Question 5

How is genetic diversity increased during fertilisation?

Answer 5

-fertilisation is random

-random fertilisation produces zygotes with different combinations of chromosomes from both parents

• this is the mixing of genetic material= increases genetic diversity within a species

Question 6

What happens to the number of chromosomes in the gametes during meiosis?

Answer 6

The chromosome number halves

Question 7

What are the characteristics of homologous pair of chromosomes?

Answer 7

-chromosomes are the same size

• have the same genes

-may have different alleles

Question 8

Describe the process of meiosis?

Answer 8

1) before meiosis, DNA unravels and replicates, so there are two copies of each chromosomes= chromatids

2) DNA the condenses forming double armed chromosomes- each made from sister chromatids joined by the centromere in the middle

3) meiosis 1- first division- the chromosomes arrange themselves into homologous pairs

4) theses homologous pairs are then separated, halving the number of chromosomes

5) meiosis 2- second division- the pairs of sister chromatids that make up each chromosome are separated as the centromere is divided

6) four haploid cells (gametes) that are genetically different are produced

Question 9

How can meiosis lead to genetic variation?

Answer 9

-crossing over

-independent segregation

Question 10

Describe the process of crossing over?

Answer 10

-happens in meiosis 1

• homologous pair of chromosomes come together and pair up

-chromatids twist around each other and bits of chromatids swap over

-which means the daughter cells produced have chromatids that contain the same genes but now have a different combination of Alleles

Question 11

Describe how independent segregation leads to genetic variation?

Answer 11

• when the homologous pairs are separated in meiosis 1, it’s random which chromosome from each pair ends up in which daughter cell
• the daughter cells produces have completely different combinations of those maternal and paternal chromosomes

-the shuffling of chromosomes leads to genetic variation in any potential offspring

Question 12

Compare mitosis and meiosis?

Answer 12

Mitosis:

-forms cells with the same number of chromosomes are the parent

• daughter cells are genetically identical
• produces 2 daughter cells

Meiosis:

-forms cells with half the number of chromosomes are the parent cell

• daughter cells are genetically different
• forms 4 daughter cells

Question 13

Why are the outcomes of mitosis and meiosis different?

Answer 13

1. Mitosis only has one division whilst meiosis has two
2. There’s no pairing or separating of homologous chromosomes in mitosis= no crossing over or independent segregation

Which means mitosis = genetically identical daughter cells