Variation

Question 1

Why might organisms vary in their phenotype?

Answer 1

Different genotype
Epigenetic modifications
Different environments.

Question 2

Define heritable variation.

Answer 2

A variation in the genes in the gametes of an organism will be passed on to the offspring.

Question 3

How does sexual reproduction generate heritable variation?

Answer 3

Crossing over
Random distribution of chromosomes in metaphase 1
Random distribution of chromatids in metaphase 2
Mixing of parental gametes at fertilisation.

Question 4

Define non-heritable variation.

Answer 4

Environmental conditions cause them. Eg differences in diet may lead to variation in body shape and size within pop of animals but the genes aren’t changed so not passed on to offspring.

Question 5

Define discontinuous variation.

Answer 5

• characteristic being displayed not affected by environment
• small number of possibilities for characteristics eg 5/6 fingers
• characteristics are discrete (clear cut and easy to tell apart)
• monogenic characteristics
• not affected by environment

Question 6

Define continuous variation

Answer 6

• phenotype may be expressed but the environment plays a part
• many possible values eg baby size 2-5kg
• values show gradation from one extreme to another
• polygenic
• considerable influence of environment

Question 7

Explain how the discontinuous variation of human height is controlled by the environment.

Answer 7

They may contain the gene to be tall, but this depends on getting the right nutrition and exercise.

Question 8

Explain how plants may show discontinuous variation and are impacted by the environment.

Answer 8

Variation in height due to light intensity or direction of growth due to light direction. without light, auxin synthesis elongates stem cells and they can’t produce chlorophyll.

Question 9

How can continuous variation be displayed?

Answer 9

Normal distribution curve with mean median mode in same place.

Question 10

Compare continuous and discontinuous variation.

Answer 10

Heritable - both
Non - heritable - continuous
Monogenic / polygenic
No environmental influence / some environmental influence
Few values / many values
Fingers discontinuous/ height continuous
Plant height discontinuous / leaves continuous