3.4.3 - Genetic diversity due to mutations or meiosis

Question 1

Define gene mutation

Answer 1

change in the base sequence of chromosomes - can arrise spontaneously during DNA replication and include base deletion and substitution

Question 2

How does base substitution result in a different amino acid sequence ?

Answer 2

• polypeptide produced will differ by one amino acid
• Two impacts:
• 1- if the amino acid is** changed** and is involved in forming bonds final protein may be a different shape and not function properly
• 2 - amino acid may not be changed as genetic code is **degenerate **- so polypeptide produced will not be effected

Question 3

How does base deletion result in a different amino acid sequence?

Answer 3

• entire amino acid sequence will be changed so polypeptide will not function correctly
• as every triplet has been shifted to the left by one base (so is read incorrectly)

Question 4

Define chromosome mutation - what are the two types

Answer 4

changes to the number or structure of chromosomes
1. polyploidy - changes in whole sets of chromosomes (eg three or more instead of two)
2. non-disjunction - homologous pairs don’t separate in meiosis so gamete has one more or one less chromosome - **number of individual chromosomes is changed **

Question 5

Define meiosis

Answer 5

produced four genetically different haploid daughter cells

Question 6

Describe the process of meiosis

Answer 6

1. First division (meiosis 1) - homologous chromosomes pair and chromatids wrap around - exchanged during** crossing over** -
2. Second division (meiosis 2) - chromatids move apart and four haploid cells are formed (each with 23 chromosomes)

Question 7

How is genetic variation achieved during meiosis?

Answer 7

1. independent segregation - homologous pairs line up at random during meiosis one which results in a random combination of chromosomes going into each daughter cell
   2.** crossing over** of maternal and paternal alleles
   - chromatids (of homologous chromosomes) twist around each other
   - tension - sections of chromatid break off and join to sections of the partner chromosome (RECOMBINATION)
   - results in new genetic combinations in the maternal and paternal alleles

Question 8

How can you calculate the number of possible combinations of chromosomes in a daughter cell

Answer 8

2^n (where n is the number of PAIRS of homologous chromosomes)

Question 9

How can you calculate the possible number of
different combinations of chromosomes
following** random fertilisation of two
gametes?**

How would crossing over and recombination impact this value?

Answer 9

( 2 ^n ) ^2
- random fertilisation of haploid gametes further increases genetic variation within a species

increase the number of possible chromosome combinations