Genetic Diversity due to Mutation and Meiosis

Question 1

what is a frame shift

Answer 1

change resulting in misreading of all nucleotides downstream, usually resulting in a truncated non-functional protein

Question 2

what type of mutations cause a frame shift and explain them

Answer 2

deletion - the removal of 1 or more bases resulting in a frame shift

addition - the adding of one or more bases resulting in a frame shift

duplication - where one or more bases is repeated causing a frame shift

Question 3

what type of mutations don’t cause a frame shift and explain them

Answer 3

inversion - a sequence of bases is reversed e.g. TAGCAGCT becomes TCGACGAT

translocation - a sequence of bases is moved from one location in the DNA molecule to another part of the genome

substitution - the replacement of one or more bases by one or more different bases

Question 4

why can a functioning protein still be formed after substitution

Answer 4

• the DNA code is degenerate meaning that an amino acid can be coded by more than 1 base triplet
• the mutation could have occured in an intron which doesn’t code for proteins
• the mutation doesn’t affect the shape of the tertiary in a way that affects the function of the protein

Question 5

difference between mitosis and meiosis (4)

Answer 5

• mitosis has one nuclear division, meiosis does two
• mitosis produces two daughter cells, meiosis produces four
• mitosis produces genetically identical cells, meiosis doesn’t
• mitosis produces cells with the same amount of chromosomes as the parent cell, meiosis produces cells with half

Question 6

what is crossover during meiosis

Answer 6

• the pair of homologous chromosomes lie side by side forming a bivalent
• the chromatids of the homologous chromosomes then intertwine
• the chromatids break and equivalent portions of the chromatids are exchanged

Question 7

how is variation (genetic diversity) achieved during meiosis

Answer 7

• independent segregation of homologous chromosomes
• genetic recombination (crossover) within homologous chromosomes

Question 8

how do you calculate the possible numbers of varied combinations of paternal and maternal chromosomes

Answer 8

2ⁿ

• n = number of homologous pairs

Question 9

what is independent segregation during meiosis

Answer 9

• during the first meiotic division, hom. chromosomes pair together and then separate so that one member from each pair enters the gamete

Question 10

what is a chiasma

Answer 10

site of crossing over

Question 11

what is genetic recombination

Answer 11

the exchange of alleles ,during cross over, producing new combinations of alleles known as recombinants

Question 12

what is nondisjunction

Answer 12

the failure of the chromosomes to separate during cell division , which produces daughter cells with abnormal numbers of chromosomes.