4.3 Genetic diversity

Question 1

What is a gene mutation?

Answer 1

• A change to the base sequence of DNA
• Can arise spontaneously during DNA replication

Question 2

What is a mutagenic agent?

Answer 2

A factor that increases rate of gene mutation (eg. UV radiation)

Question 3

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

Answer 3

• Changes base triplets in DNA so changes sequence of codons in mRNA
• Changes sequence of amino acids
• Changes position of hydrogen/ionic bonds
• Changes tertiary structure

Question 4

Substitution

Answer 4

a base is replaced with another base in DNA

Question 5

Deletion

Answer 5

one or more bases are added to the DNA base sequence

Question 6

What is meant by a frameshift?

Answer 6

• Occurs when mutations change the number of bases by a number not divisible by 3
• Shifts the way the genetic code is read, altering all triplets downstream

Question 7

What are homologous chromosomes?

Answer 7

Pairs of chromosomes that have the same genes at the same loci but different alleles

Question 8

What is the difference between haploid and diploid cells?

Answer 8

• Haploid have a single set of chromosomes (n)
• Diploid have 2 complete set of chromosomes (2n)

Question 9

What happens during meiosis?

Answer 9

• During interphase, DNA replicates
• During meiosis I, homologous chromosomes separate
• During meiosis II, sister chromatids separate
• Resulting in 4 genetically different haploid daughter cells

Question 10

What happens during crossing over?

Answer 10

• Homologous pairs of chromosomes associate
• Chiasmata form between chromatids
• Alleles / equal lengths of chromatids are exchanged between chromosomes
• Creating new combinations of alleles

Question 11

What happens during independent segregation?

Answer 11

• Homologous pairs of chromosomes randomly align at equator
• So it it random which chromosome from each pair goes into each daughter cell
• Creating different combinations of maternal and paternal chromosomes

Question 12

Why is meiosis important?

Answer 12

• Two divisions makes haploid gametes
• So diploid number is restored at fertilisation so chromosome number is maintained between generations
• Independent segregation and crossing over creates genetic variation

Question 13

How do mutations in number of chromosomes arise?

Answer 13

• Spontaneously by chromosome non-disjunction during meiosis
• Homologous chromosomes or sister chromatids don’t separate properly
• So some gametes have an extra copy of a chromosome and others have none