9: Genetic diversity

Question 1

Gene mutations

Answer 1

Change in the base sequence of dna. gene mutations occur randomly during dna replication
- random mutations are more likely to occur if exposed to mutagenic agents which interfere with dna replication (radiation and chemicals)

Question 2

What does a gene mutation do to the base sequence

Answer 2

• deletion
• substition
  deletion would case a frame shift as removal of one base changes all subsequent codons which is more harmful as an amino acid may be incorrectly coded for,
  substitution may have no impact as the new codon may still code for the same amino acid as the genetic code is generate.

Question 3

Chromosome mutation

Answer 3

• occurs in non disjunction. this is where the chromosomes do not split equally during anaphase
• this can occur in two forms; either changes in the whole sets of chromosomes (polypoidy) or changes in individual chromosomes (aneuploidy)

Question 4

Polypoidy

Answer 4

• changes in the whole sets of chromosomes
• organisms have three or more copies of chromosomes rather than 2
• meisosis all pulled to one side by spindle fibres

Question 5

Aneuploidy

Answer 5

• Changes in the number of individual chromosomes
• homologous pairs of chromosomes fail to seperate in meiosis
• non disjunction. results in gamete having one more or one fewer chromosome
• downsyndrome

Question 6

Meiosis

Answer 6

• produces four genetically different haploid gametes by two nuclear divisions. makes sperm and egg cells
• diploid parent cell 2n dividing to become a haploid cell

first division; homologous pairs separate. one chromosome from each pair going into one of the two daughter cells

second division: chromatids seperate, producing 4 haploid daughter cells

interphase, then PMAT x2

Question 7

Difference between mitosis and meiosis

Answer 7

• mitosis produces two genetically identical daughter cells, with the same number of chromosomes as parent cell
• meiosis produces four daughter cells, with half the amount of chromosomes as parent cell

Question 8

Two mechanisms in meiosis which introduce variation

Answer 8

• independent segragation of homologous chromosomes
• crossing over of homologous chromosomes

Question 9

Crossing over

Answer 9

• occurs between homologous pairs of chromosomes in prophase 1
• homologous pairs twist round each other
• broken off pieces of chromatids combine with another chromatid
• recombination

Question 10

Independant segragation

Answer 10

• homologous pairs of chromosomes line up opposite each other at the equator of cell
• its random which side of the equator the maternal and paternal chromosomes of each homolgous pair lie
• pairs are seperated so each of homologous pair ends up in the daughter cell
• this creates large number of possible combinations of chromosomes in the daughter cells produced
  2n

Question 11

Genetic diversity

Answer 11

number of different alleles of genes in a population
- enables natural selection which leads to evolution

Question 12

Evolution

Answer 12

change in allele frequency over many generations in a population

Question 13

Process of natural selection

Answer 13

• new alleles for a gene are created by random mutations
• if new alleles increasing chances of surviving, more likely to survive and reproduce
• reproduction passes on advantageous allele
• over many generations, new allele increases in frequency in population (more common in gene pool)

Question 14

Types of selection

Answer 14

• directional (one of the extremes has the selective advantage, occurs when change in environment). the model trait changes
• stabilising (the modal trait has the selective advantag. occurs when no change in environment. model trait stays the same. standard deviation decreases