Topic 15 - Inheritance and Evolution

Question 1

Variation

Answer 1

Differences between individuals of the same species. Variation can be genetic, environmental, or a combination of both.

Question 2

How genetic variation is produced

Answer 2

Random fusion of gametes at fertilisation means each zygote will have a unique combination of alleles. This is because an egg cell can be fertilised by a single sperm out of millions of sperm cells.

Question 3

Female sex chromosomes

Answer 3

XX

Question 4

Male sex chromosomes

Answer 4

XY

As only a father can pass on a Y chromosome, he is responsible for determining the sex of the child

Question 5

Allele

Answer 5

A different version of the same gene

Question 6

Phenotype

Answer 6

Physical, observable characteristics of an organism (e.g. eye colour, hair colour)

Question 7

Genotype

Answer 7

The genetic makeup of an organism - the combination of alleles that control each characteristic (e.g. RR, Rr, rr)

Question 8

Homozygous

Answer 8

Having only one type of allele present (i.e. BB or bb)

Question 9

Heterozygous

Answer 9

Having two different types of allele present (i.e. Bb or bB)

Question 10

Dominant allele

Answer 10

A version of a gene that, if present, is always expressed

Question 11

Recessive allele

Answer 11

A version of a gene that is only expressed if two copies are present

Question 12

Monohybrid inheritance

Answer 12

Inheritance of a single characteristic/trait. These characteristics are controlled by a single gene.

Question 13

Pedigree rules

Answer 13

1. Dominant disorders can’t jump generations but recessive ones can. With recessive disorders, two non-sufferers can have a child who has the disease
2. It is impossible for two people with a recessive disorder to have children without the disorder as their genotypes will be ff x ff
3. It is possible for two people with a dominant disorder to have children without the disorder. This is because their genotypes can be Hh and Hh

Question 14

Polygenic

Answer 14

Characteristics that are controlled by more than one gene (e.g. eye colour is controlled by several genes, so the wide range of combinations make it difficult to show on a genetic diagram)

Question 15

Codominance

Answer 15

When both alleles within a genotype are expressed in the phenotype of an individual (e.g. alleles A and B are codominant, so the blood type will be AB)

Question 16

Mutation

Answer 16

A rare, random change in the sequence of bases in DNA

Question 17

How mutations can affect phenotype

Answer 17

• when mutations change the base sequence of DNA, the base sequence of the complementary mRNA transcript also changes
• modified mRNA transcript will be translated to code for different amino acids, changing the structure of the chain
• the function of protein is altered

Question 18

Effects of mutations

Answer 18

• most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
• a small number of mutations code for a significantly altered protein with a different shape, which may affect the protein’s function (e.g. collagen may lose its strength if shape changes)

Question 19

Causes of mutations

Answer 19

Frequency of mutations can be increased by:
- exposure to gamma rays, x-rays and UV rays (ionising radiation)
- exposure to chemicals (e.g. tar in tobacco)

Question 20

Evolution

Answer 20

the change in the characteristics of a species over time (millions of years), occurring through the process of natural selection

Question 21

Darwin’s Theory of Evolution

Answer 21

• individuals show a wide range of variation caused by differences in genes and mutations
• individuals with characteristics that are most suited to the environment are more able to survive and reproduce
• these characteristics are passed on at a higher rate than less suited characteristics, becoming more common in the population