Variation and inheritance

Question 1

Cause of variation:

Answer 1

• Mutations changing the genetic code
• They are random and constantly take place

Question 2

Variation:

Answer 2

• Environmental variation
• Genetic variation

Question 3

Chlorosis:

Answer 3

• Cells do not produce the normal amount of chlorophyll, so it can not make food by photosynthesis.
• Leaves have a pale or yellow colour

Question 4

Variation leading to chlorosis:

Answer 4

• Have normal genes coding for chlorophyll production
• Due to environmental factors.

Question 5

Examples of environmental factors leading to chlorosis:

Answer 5

• Lack of light
• Mineral deficiencies
• Virus infections

Question 6

How lack of light causes chlorosis:

Answer 6

• In absence of light, plants turn off their chlorophyll production to conserve resources.

Question 7

How mineral deficiencies cause chlorosis:

Answer 7

• Lack of iron or magnesium.
• Iron is needed as a cofactor by some enzymes that make chlorophyll
• Magnesium is found at heart of the chlorophyll molecule.
• If ever elements are lacking, plant can not make chlorophyll and leaves become yellow.

Question 8

How virus infections cause chlorosis:

Answer 8

• When viruses infect plants, they interfere with the metabolism of cells.
• Common symptom is yellowing of infected leaves as they can no longer support synthesis of chlorophyll.

Question 9

What changes animal body mass?

Answer 9

• Caused by genetic and environmental factors.

Question 10

Environmental impacts on animal body mass:

Answer 10

• Amount of / quality of food
• Quantity of exercise which the organism gets
• Presence of disease

Question 11

Genetic variation that causes obesity in mice?

Answer 11

• Genetic make-up of an organism.
• Mutation on chromosome 7 that produces leptin.
• Causes pattern of fat deposit in the body to be altered
• Gene acts in conjunction with other genes that regulate the energy balance of the body.

Question 12

Creating genetic variation:

Answer 12

• 2 alleles inherited (one from each parent)
• Alleles can be same or different

Question 13

Genotype:

Answer 13

• The combination of alleles an organism inherits for a characteristic

Question 14

Pheontype:

Answer 14

• The observable characteristics of an organism

Question 15

Modifications:

Answer 15

Changes to the phenotype by the environment, not inherited.

Question 16

Where do mutations need to occur for them to be passed onto offspring?

Answer 16

Gamete

Question 17

Is is always possible to determine an organism’s genotype from its phenotype?

Answer 17

No because some alleles are dominant.

Question 18

Dominant allele

Answer 18

The version of the gene that will always be expressed if present in an organism.

Question 19

Recessive allele

Answer 19

Will only be expressed if two copies of the allele are present in an organism.

Question 20

Homozygous

Answer 20

They have two identical alleles for a characteristic.

Question 21

Homozygous dominant

Answer 21

Contains two alleles for the dominant phenotype

Question 22

Homozygous recessive

Answer 22

Contain two alleles for the recessive phenotype

Question 23

Heterozygous

Answer 23

They have two different alleles for a characteristic. In this case the dominant phenotype will be expressed.

Question 24

Continuous variation:

Answer 24

A characteristic that can take any value within a range, with two extremes.

Question 25

Discontinuous variation

Answer 25

A characteristic that can only appear in specific (discrete) values

Question 26

Cause of continuous variation

Answer 26

Genetic and environmental

Question 27

Cause of discontinuous variation

Answer 27

Mostly genetic

Question 28

Genetic control of continuous variation

Answer 28

Polygenes - controlled by a number of genes

Question 29

Genetic control of discontinuous variation

Answer 29

One or two genes

Question 30

Examples of continuous variation:

Answer 30

- Leaf surface area - Animal mass - Skin colour

Question 31

Discontinuous variation examples:

Answer 31

- Blood groups - Albinism - Round and wrinkled pea shape

Question 32

Etiolation

Answer 32

Plants grown in dark have weak stems and small leaves as they have grown very fast towards light.