3.4.2 Genetic Diversity

Question 1

How can a gene mutation result in a protein not being synthesised?

Answer 1

Mutation changes sequence of bases, A premature stop codon or frame shift is changed by the mutation. Transcription/translation does not occur

Question 2

What are gametes?

Answer 2

The male and female sex cells found in all organisms that reproduce sexually

Question 3

Why is it important that gametes only have one set of chromosomes ?

Answer 3

So that the diploid number of chromosomes can be restored after fertilisation

Question 4

Describe a haploid nucleus

Answer 4

One set of chromosomes, half the number of chromosomes found in a normal body cell. Contains one chromosome from each homologous pair, type of nucleus found in gametes

Question 5

Describe a diploid nucleus

Answer 5

Two sets of chromosomes

Question 6

Describe meiosis

Answer 6

Type of cell division that produces gametes, 4 haploid daughter cells are produced

Question 7

Define genetic variation

Answer 7

Differences that exist between individual’s genetic material

Question 8

How does meiosis produce cells that are genetically different ?

Answer 8

Through crossing over of chromatids and independent assortment of chromosomes

Question 9

Explain the crossing over process

Answer 9

During first division in meiosis, the homologous pairs of chromosomes come together and pair up. Two of the chromatids in each homologous pair twist around each other. the twisted bits break off their original chromatid and rejoin on the other chromatid, recombining their genetic material, exchanging sections of DNA.

Question 10

How does crossing over increase genetic variation ?

Answer 10

Each four new cells formed from meiosis contains chromatids with different combinations of alleles

Question 11

Describe independent assortment

Answer 11

The random distribution of different chromosomes in the gametes. When gametes are produced, different combinations of the maternal and paternal chromosomes go into each cell. Only one chromosome from each pair ends up in each gamete

Question 12

Explain the importance of meiosis in gametes production

Answer 12

To half the chromosome number producing a haploid nucleus, so at fertilisation the diploid number of chromosomes is restored. It allows genetic variation through independent assortment and crossing over.

Question 13

Why does asexual reproduction lead to low genetic diversity ?

Answer 13

Low genetic diversity means there are few different alleles in the gene pool. Asexual reproduction leads to all offspring being genetically identical. No meiosis.

Question 14

What is a mutation?

Answer 14

Change to the base sequence of DNA. Caused by errors during DNA replication

Question 15

What is a substitution mutation?

Answer 15

When one base is substituted with another

Question 16

What is a deletion mutation?

Answer 16

When one base is deleted

Question 17

What is an insertion mutation?

Answer 17

When an extra base is added

Question 18

What is an duplication mutation?

Answer 18

Duplication - one or more bases are repeated

Question 19

What is a point mutation?

Answer 19

Point mutation - a change in a single nucleotide

Question 20

What is a frame shift mutation?

Answer 20

Frame shift mutation - the reading frame changes and this results in a different protein structure

Question 21

What’s the difference between a DNA mutation and a chromosome mutation?

Answer 21

Mutation = change in the DNA. Chromosome mutation = changes in the structyre or number of whole chromosomes. E.g. an organism having an extra chromosome

Question 22

Define ‘allele frequency’

Answer 22

The frequency of a particular allele in a gene pool

Question 23

Distinguish between stabilising selection and directional selection

Answer 23

Directional selection causes changes in the allele frequency so the norm curve shifts in one direction. Stabilising selection favours the organisms closest to the mean and selects against those at the extremes so the norm curve becomes ‘squashed’

Question 24

Answer 24

Question 25

Answer 25