Genetic Diversity And Adaptation

Question 1

Describe what is a gene mutation

Answer 1

• change to the quantity of bases or base sequence in the DNA
• results in a change of amino acid sequence of the polypeptide. Altering tertiary structure and function
• can arise spontaneously during DNA replication

Question 2

What are the two forms of gene mutation

Answer 2

Base substitution and base deletion

Question 3

Describe base substitution

Answer 3

• nucleotide is replaced changing the codon
• genetic code degenerate so may result in same amino acid
• could alter amino acid, changing tertiary structure/ R group interactions
• results in a stop codon

Question 4

Describe base deletion

Answer 4

• nucleotide removed
• alters reading frame
• all codons/amino acids altered from that point

Question 5

Describe introns and exons in eukaryotes

Answer 5

• introns non-coding sequences of DNA
• are transcribed then spliced from pre-mRNA in the nucleoplasm
• mature mRNA left to be translated (only contain exons)

Question 6

Describe how base substitution alters protein function

Answer 6

• alters single base, altering codon
• may encode for a different amino acid/r group
• affecting r group interactions altering polypeptide folding/tertiary structure
• polypeptide dysfunctional

Question 7

Describe a silent mutation

Answer 7

• base substitution results in a codon that encodes for the same amino acid
• polypeptide is not affected

Question 8

What are mutagenic agents

Answer 8

What alters the base sequence of dna

Question 9

Name some mutagenic agents

Answer 9

• Ionic radiation (UV light, X rays)
• Asbestos
• Carcinogens (chemicals e.g. tobacco)

Question 10

Describe a diploid cell

Answer 10

2n chromosomes. Homologous pairs of each type. Products of fertilisation.

Question 11

Describe a haploid cell

Answer 11

n chromosomes. One of each type. Are gametes or ‘sex cells’.

Question 12

What is ‘n’

Answer 12

Number of types of chromosomes an organism has

Question 13

Describe the human life cycle

Answer 13

• both diploid parents produce haploid gametes through meiosis
• 2 haploid gametes fuse together to form a diploid zygote
• zygote grows by mitosis

Question 14

What are alleles

Answer 14

Alternate versions of the same gene
- process a different nucleotide base sequence which may alter polypeptide the gene encodes for

Question 15

What are homologous chromosomes

Answer 15

• 2 chromosomes that posses the same genes at the same gene loci
• may not posses the same alleles. Are located in diploid cells (2n)
• made up of one paternally derived male gamete and one maternally derived female gamete

Question 16

Describe division one of meiosis

Answer 16

• homologous chromosomes pair up in synapsis
• ‘crossing over’ rearranges alleles on homologous chromosomes
  -‘independent segregation’ of homologous chromosomes to produce 2 haploid cells

Question 17

Describe division 2 of meiosis

Answer 17

• cells align single chromosomes in metaphase 2
• chromatids are separated
• produces 4 genetically non-identical haploid cells

Question 18

5 differences between mitosis and meiosis

Answer 18

1 division / 2 divisions
Produces 2 daughter cells (2n dioloid) / produces 4 daughter cells (n haploid)
Genetically identical / genetically non-identical
Growth + repair / sexual reproduction
Only chromatids separates / 2nd division separates chromatids

Question 19

Describe non disjunction

Answer 19

Failure to separate a pair of homologous chromosomes in meiosis 1. Gametes will either have an extra chromosome or one missing

Question 20

Define genetic diversity

Answer 20

Total number of different alleles in a population

Question 21

Define a population

Answer 21

A group of individuals of the same species that live in the same place and can interbreed to produce fertile offspring

Question 22

Name 5 sources of genetic variation

Answer 22

• random mutation
• crossing over
• independent segregation
• random fertilisation
• random breeding

Question 23

Describe natural selection

Answer 23

• reproductive successes of individuals affect allele frequency in populations
• random mutations of genes result in new alleles
• may result in a selective advantage over others
• individuals better adapted and more likely to survive and breed successfully when faced with particular selective pressures
• advantageous alleles passed onto the next generation
• over many generations these will increase in frequency within a population
• less advantageous allies decrease in frequency

Question 24

Describe directional selection in bacteria

Answer 24

• antibiotics act as a selective pressure
• spontaneous, random gene mutation
• new protein produced
• increased resistance to an antibiotic
• resistant bacteria survive and reproduce by binary fission
• susceptible bacteria die
• frequency of resistant bacteria increases
• population ‘normal distribution’ curve shifts in direction of population becoming more resistant