Question 2 of 2

Question 1

differences between mitosis and meiosis

Answer 1

Mitosis

• 2 identical daughter cells
• 46 chromosomes (diploid)
• Function; growth and repair
• Somatic daughter cells produced

Meiosis

• 4 different daughter cells
• 23 chromosomes (haploid)
• Function; production of gametes
• Gametes produces

Question 2

Variation

Answer 2

• Difference between individuals of the same species
• Allows for survival in their environment
• Variation occurs through;
- Random assortment of chromosomes
- Crossing over
- Non-disjunction
- Random fertilisation

Question 3

random assortment

Answer 3

® When cells divide by meiosis to form sex cells, chromosomes are copied
® Chromosomes are separated twice
® Direction that the chromosomes move is totally random
- Results in millions of different combinations

Question 4

crossing over

Answer 4

® Occurs when a small section of chromosomes swaps with a small section of a homologous pair
- Results in sex cells carrying different alleles of a gene

Question 5

Non-disjunction

Answer 5

® When a chromosomes pair do not separate properly during meioisis
- Down syndrome is caused by non-disjunction

Question 6

Random fertilisation

Answer 6

® Male releases millions of sperm, each slightly different
® 50% of sperm carry ‘X’’ chromosome and 50% carry ‘Y’ chromosome
® Thus, gender selection is random
- Gender depends on which sperm fertilises the egg

Question 7

Cancer

Answer 7

® Uncontrolled cell division occurring in mature organisms
® Causes abnormal tissue growths
® Neoplasm:
- Abnormal growth of tissue
- Three types; Benign, Malignant and Potentially malignant

Question 8

Gene mutation

Answer 8

Proto-oncogenes - normally function to stimulate cell growth
• When mutated, become oncogenes which cause uncontrolled cell division

Tumour suppressor genes - normally function to slow cell division, inhibiting division of unhealthy cells
- When mutated, uncontrolled cell division can occur

Inherited genes - variants in genes which can increase the risk of cancer
- E.g breast cancer is associated with mutations in BRCA1/BRCA2 genes

Question 9

factors that cause cancer

Answer 9

• Genetics -> proto-oncogenes etc
• Environment -> physical, chemical, biological
• Loss of immunity -> weakened immune system