Inheritance

Question 1

Define codominance

Answer 1

Both alleles express themselves equally in the heterozygous condition, resulting in a phenotype that is intermediate between its pure-bred parents.

Question 2

Dominant allele

Answer 2

Always expresses itself when present. It can express itself in the homozygous and heterozygous condition

Question 3

Recessive allele

Answer 3

Only expresses itself in the homozygous condition. It is not expressed in the presence of a dominant allele

Question 4

Discontinuous vs Continuous Variation

Answer 4

1. DV: Involves a few clear-cut phenotypes that can be placed into fixed categories.
   CV: Involves a RANGE of phenotypes with intermediates that can be distributed across a continuum
2. DV: Controlled by 1 or a few genes
   CV: Controlled by many genes
3. DV: Phenotypes not affected by environmental factors
   CV: Affected by environmental factors.
4. DV: Genes do not show an additive effect
   CV: Genes show an additive effect

Question 5

Albinism Gene Mutation

Answer 5

• Recessive Gene mutation
• Results in lack of melanin, the pigment for skin, hair & eye colour
• Without melanin, they have poor eyesight and are more sensitive to sunlight.

Question 6

Sickle Cell Anaemia Gene Mutation

Answer 6

Cause:
- Recessive gene mutation
- Single base mutation, resulting in a different amino acid being coded for red blood cells.

Effect:
- Results in sickle shaped red blood cells
- Transport of oxygen is poor
- RBCs more fragile
- RBCs tend to agglutinate

Question 7

Down Syndrome Chromosome Mutation

Answer 7

Cause:
- During fertilisation, either sperm or egg has 2 copies of chromosomes 21
- Results in 3 copies of chromosome 21 in the individual’s body cells.

Effect:
- Unable to reproduce
- Intellectual capacity reduced

Question 8

Things that speed up mutation

Answer 8

• Radiation like UV rays and gamma rays
• Chemicals like tar and formaldehyde