Genetic diversity can arise as a result of mutation or during meiosis

Question 1

What is a genetic mutation?

Answer 1

a change in the base sequence of DNA that can rise spontaneously during DNA replication

Question 2

What is a mutagenic agent?

Answer 2

a factor that increases the rate of gene mutation e.g. UV light or alpha particles

Question 3

How can a mutation lead to the production of a non-functional enzyme?

Answer 3

• changes the sequence of base triplets in DNA so changes codons on mRNA
• changes the sequence of amino acids in the polypeptide
• so changes the position of hydrogen/ionic/disulfide bonds
• so changes the tertiary structure of a protein
• enzymes - active site changes shape so enzyme-substrate complex can’t form

Question 4

What are the possible effects of a substitution mutation?

Answer 4

• DNA base is replaced by a different base
• this changes one triplet so changes one mRNA codon
• so some amino acid in the polypeptide chain changes - tertiary structure may change position of H/ionic/disulfide bonds
• or amino acid doesn’t change due to the degenerate nature of the genetic code where OR if mutation is in an intron so is removed by splicing

Question 5

What are the possible effects of a deletion mutation?

Answer 5

• one nucleotide is removed from the DNA sequence
• changes the sequence of DNA triplets from point of mutation
• changes sequence of mRNA codons after point of mutation
• changes sequence of amino acids in primary structure of polypeptide
• changes position of H/ionic/disulfide bonds so changes tertiary structure

Question 6

What are some features of homologous chromosomes?

Answer 6

• same length
• same genes at same loci
• may have different alleles

Question 7

What is the difference between diploid & haploid cells?

Answer 7

• diploid has 2 complete set of chromosomes - 2n
• haploid has a single set of unpaired chromosomes - n

Question 8

How does a cell divide by meiosis?

Answer 8

• DNA replicated during interphase to produce 2 copies of each chromosome
• meiosis 1 separates homologous chromosomes into pairs - involves crossing over & independent segregation
• meiosis 2 separates chromatids
• produces 4 genetically varied haploid daughter cells

Question 9

Why is the number of chromosomes halved during meiosis?

Answer 9

homologous chromosomes are separated during meiosis 1

Question 10

How does crossing over create genetic variation?

Answer 10

• homologous pairs of chromosomes form a bivalent
• chiasmata form
• alleles of equal lengths of the chromatids are exchanged between chromosomes
• this creates new combinations of alleles on chromosomes

Question 11

How does independent segregation create genetic variation?

Answer 11

• homologous pairs randomly align at the equator
• this creates different combinations of maternal & paternal chromosomes