17.1. Variation

Question 1

Variation

Answer 1

Differences in the Phenotype of individuals belonging to the same population

Question 2

Continuous (quantitative) Variation

Answer 2

Occurs when a feature can have any value between 2 extremes, such as height and mass in humans
- caused when the effects of many genes act together to influence a characteristic and the environment can have an effect
- different alleles at a single gene locus have small effects
on the phenotype
- different genes have the same, often additive, effect on the phenotype
- a large number of genes may have a combined effect on a particular phenotypic trait; these genes are known
as polygenes.

Question 3

Discontinuous (qualitative) Variation

Answer 3

Occurs when a feature only has a few distinct categories such as blood groups in humans
- caused by one or few genes that control the characteristic, with little or no influence from the environment
- different alleles at a single gene locus have large effects
on the phenotype
- different genes have quite different effects on the
phenotype.

Question 4

Environmental effects of phenotype

Answer 4

One individual might have less food, or less nutritious

food, than another with the same genetic contribution, so this influences the phenotype

Question 5

Variation in Hair Colour of Cats

Answer 5

• At least 8 genes at different loci determine hair colouring of cats. These are known as polygenes
• Depending on the combination of alleles that a cat has for each of these genes, it can have a wide range of colours
• The cat hair colour genes exert their effect by coding for the production of enzymes
• One such gene is found at the C locus
• Siamese cats have 2 copies of this recessive allele called Cs
• This gene codes for an enzyme that is sensitive to temperature
• The extremities are the coldest parts of the animal, so the dark colour is produced there.
• Lighter hair is at warmer parts of the body

Question 6

Variation in Human Height

Answer 6

• also affected by many different genes at different loci
• even if a person inherits alleles of these genes that give the potential to grow tall, they will not grow tall unless the diet supplies plenty of nutrients to allow this to happen
• poor nutrition, especially in childhood, reduces the maximum height attained

Question 7

Cancer

Answer 7

• risk of developing cancer is influenced by both genes and the environment
• for example, a woman with particular alleles of the genes BRCA1 and BRCA2 has a 50-80% higher chance of developing breast cancer at some stage of her life
• the environment, such as by smoking, can increase the risk of cancer, though

Question 8

Why genetic variation is important in selection

Answer 8

advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population

Question 9

T-test

Answer 9

Used to determine whether the variation shown in the population is significantly different from the variation in another population

Question 10

What can the T-test tell you?

Answer 10

If there is a statistically significant difference between 2 means, when:

• Continuous data has been collected
• The data is from a population that is normally distributed
• Standard deviations are approximately the same
• The two samples have fewer than 30 values each