3.4.3 genetic diversity can arise as a result of mutation or during meiosis

Question 1

what can a gene mutation involve?

Answer 1

• change in the base sequence of chromosomes
• can arise spontaneously

Question 2

what are the types of gene mutation?

Answer 2

deletion and substitution

Question 3

why do some substitution mutations not result in a mutation?

Answer 3

• due to the degenerate nature of the genetic code
• some amino acids are coded for by more than one DNA triplet code
• not all substitutions result in a change in the primary structure

Question 4

what are mutagenic agents?

Answer 4

• external influences that induce mutations

Question 5

how do mutagenic agents increase the rates of mutations?

Answer 5

• certain chemicals can remove groups from nucleotide bases
• other chemicals can add groups to nucleotides

Question 6

what does meiosis produce?

Answer 6

daughter cells that are genetically different from each other

Question 7

outline interphase

Answer 7

• happens before meiosis
• chromosomes replicate to form 2 sister chromatids joined at a centromere

Question 8

outline prophase I

Answer 8

• chromosomes condense and become visible
• homologous pairs of chromosomes come together to form a bivalent
• adjacent chromatids exchange genes during crossing over

Question 9

outline metaphase I

Answer 9

• nuclear membrane broken down
• spindle fibres produced at centrioles
• bivalents move to the equator of the cell
• centromeres attach to spindle
• positioning of homologous pairs is random ( independent segregation)

Question 10

outline anaphase I

Answer 10

• homologous chromosomes are pulled apart
• by contraction of spindle fibres

Question 11

outline telophase I

Answer 11

• chromosomes group together at the poles of the cell
• the spindle disappears
• nuclear envelope reforms

Question 12

outline prophase II

Answer 12

• 2 haploid cells divide a 2nd time
• new spindle begins to form in each cell

Question 13

outline metaphase II

Answer 13

• chromosomes line up on the equator of the spindle
• chromatids may not be identical but instead recombinants

Question 14

outline anaphase II

Answer 14

• chromatids are pulled apart by protein spindles contracting
• centromeres divide and chromatids move to opposite poles of the cell

Question 15

outline telophase II

Answer 15

• spindle fibres breakdown
• nuclear envelope reforms around separated chromosomes

Question 16

outline the importance of meiosis

Answer 16

• reduces number of chromosomes in a cell before fertilisation
• fusion of gametes restores diploid number
• results in new combinations of alleles increasing genetic diversity

Question 17

how does random fertilisation increase genetic diversity?

Answer 17

random fertilisation produces a zygote with different combinations of chromosomes and so different combinations of alleles