Genetics - Variation

Question 1

What are the two types of variation?

Answer 1

Inherited and acquired

Question 2

For inherited variation, what are the two types?

Answer 2

Discrete/discontinuous (only a few variations for a feature)

Continuous (many variations for a given trait)

Question 3

What genetic substance determines our features?

Answer 3

The DNA in our genes

Question 4

What is DNA?

Answer 4

Genetic material made up of repeating nucleotides, arranged in a double helix that codes for our features

Question 5

What is a gene?

Answer 5

Small sections of DNA that are found on chromosomes that determine our features

Question 6

What is a chromosome?

Answer 6

A long chain of DNA that contains genes

Question 7

What is an allele?

Answer 7

Different versions of a gene

Question 8

Explain how DNA determines your phenotype

Answer 8

The base sequence on DNA determines the type of protein formed which gives you your phenotype

Question 9

Explain how different alleles for a gene give different phenotypes

Answer 9

Different alleles for a gene have different base sequences in their DNA. Therefore they produce different proteins and therefore produce different phenotypes

Question 10

What type of cell division creates variation?

Answer 10

Meiosis

Question 11

What is the purpose of meiosis?

Answer 11

A type of cell division that produces gametes (sex cells)

Question 12

Where does meiosis occur?

Answer 12

In sex organs such as testes and ovaries

Question 13

How does meiosis create variation?

Answer 13

Gametes are haploid (only have half the genetic information from each parent) which means they only have one chromosome from each homologous pair from each parent. When two gametes join during fertilisation they form a zygote which is diploid (chromosomes are now pairs again). The offspring is a combination of chromosomes and hence alleles from both parents and so is genetically unique

Question 14

What processes occur during meiosis to ensure that each gamete produced is genetically different?

Answer 14

Independent assortment

Crossing over/recombination

Question 15

Define independent assortment and explain how it creates variation

Answer 15

The random way different homologous chromosomes line up along the cell equator during meiosis. This means that each gamete receives a unique combination of chromosomes and hence alleles which increases variation.

Question 16

Define crossing over/recombination and explain how it creates variation

Answer 16

When parts of homologous chromosomes are swapped during meiosis. This creates new allele combinations in the gametes that would not normally be possible which increases variation.

Question 17

What other process creates variation but doesn’t necessarily occur during meiosis?

Answer 17

Mutations

Question 18

Define a mutation and explain what they create

Answer 18

Any change in the base sequence of DNA. Mutations create new alleles that were not present before

Question 19

What causes mutations?

Answer 19

Mutagens - radiation. certain chemicals

Question 20

Explain how a mutation might create variation

Answer 20

A mutation is any change in the base sequence of DNA. This creates new alleles and therefore new proteins. This then leads to new phenotypes

Question 21

When might a mutation be inherited?

Answer 21

If it is a gametic mutation it might be. These are mutations that occur in sex cells/gametes but the gamete would have to be involved in fertilisation

Question 22

When will a mutation not be inherited?

Answer 22

If it is a somatic mutation in won’t be inherited. These occur in body cells (not cells in sex organs involved in meiosis). The mutation may affect the organism who has the mutation though providing it causes a change in the protein formed.

Question 23

Why are mutations classified as the ‘ultimate source of variation’ but independent assortment and crossing over/recombination are not?

Answer 23

Mutations create new alleles and hence new proteins and phenotypes that were never present before. Independent assortment and crossing over/recombination simply rearranges existing alleles into new combinations.