B1 - Variation, Characteristics and Inherited Disorders

Question 1

Describe the link between genes, chromosomes and DNA. What do genes control?

Answer 1

Chromosomes are made of DNA. A particular part of a chromosome is a gene. Each gene is a length of DNA.

Genes control the development of a particular characteristic.

Question 2

What 3 main things cause genetic variation?

Answer 2

• Mutations
• Formation of gametes
• Fertilisation

Question 3

What environmental factors can cause mutations?

Answer 3

• chemicals ( tar) in tobacco smoke
• chemicals used for dying materials
• ultraviolet radiation in sunlight
• ionising radiation like X - rays and gamma rays

Question 4

What is an allele?

Answer 4

When a mutation changes a gene to a different version. It still codes for the same characteristic but will produce a different version of it.

Question 5

Why does gamete formation produce genetic variation?

Answer 5

• during the cell division , the chromosomes in each pair may swap places with each other, giving different combinations of alleles
• the way the two copies of chromosomes separate from each other during the second meiotic division is random

This means each gamete is genetically unique

Question 6

Why does fertilisation produce variation?

Answer 6

Fertilisation is random

• each egg produced by the mother is genetically different from the other eggs she makes
• the father makes many sperms and any one of them could join with an egg

Question 7

What is the difference between genotype and phenotype?

Answer 7

Genotype - the genes you inherit from your parents

Phenotype - the physical expression of the genes

Question 8

What is heterozygous and homozygous?

Answer 8

Heterozygous - two different versions of the gene coding for a characteristic
Homozygous - the same version of the gene coding for a characteristic

Question 9

What are inherited disorders caused by? Examples?

Answer 9

Caused by faulty genes.

E.g sickle cell anaemia, cystic fibrosis, red - green colour blindness