Biology: DNA, Genes and Cell Division

Question 1

How many chromosomes are in the nucleus of human cells ?

Answer 1

46 chromosomes, 22 pairs and 2 sex chromosomes

Question 2

What are present in chromosomes?

Answer 2

each chromosomes contains thousands of genes made up of chains of DNA nucleotides
- nucleotides consist of sugar molecule (deoxyribose), a phosphate group and one of the four possible nitrogenous base pairs (adenine, cytosine, guanine and thymine)

Question 3

What is the each rung of DNA like?

Answer 3

each rung in the DNA double stranded helix ladder is an A to T or C to G

Question 4

What is a gamete?

Answer 4

diploid egg and sperm cells precursor cells divide by meiosis to produce male and female haploid gametes with nuclei that contain 23 chromosomes
These fuse during fertilisation to produce a new cell, the zygote which has a single diploid nucleus

Question 5

What happens during meiosis?

Answer 5

diploid cells divide twice- once to give 2 diploid cells (DNA duplicated) and then once more to give 4 different haploid cells, each with a single gene copy of each chromosome (creates genetic variability)

Question 6

What happens after fertilization ?

Answer 6

after fertilisation the diploid chromosome number is restored

Question 7

What cells are suitable to become gametes?

Answer 7

only haploid cells, produced by meiosis and containing half the number if chromosomes

Question 8

What are somatic cells?

Answer 8

these are non-sex cells that replicate by mitosis to produce 2 identical diploid daughter cells with same number of chromosomes as all other somatic cells including zygote from which they originate

Question 9

What is interphase?

Answer 9

cell growth and DNA replication

then mitosis in four phases occurs

Question 10

What are the 4 phases of mitosis?

Answer 10

prophase- chromosomes visible in nucleus and nuclear membrane dissolves
metaphase- line up along equator
anaphase- chromosomes moves apart
telophase- nuclear membrane form and the cell divides in 2