Genetics

Question 1

What is Evolution?

Answer 1

• Changes in allele frequency occur through:
• Non-random processes - natural selection & sexual selection
• Random process - genetic drift

Question 2

Sexual selection

Answer 2

involves the selection of alleles that increase the individual’s chances of mating and producing offspring. Sexual selection may lead to sexual dimorphism.

Question 3

Genetic drift

Answer 3

occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next

Question 4

Fitness

Answer 4

measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species

Question 5

Co-evolution

Answer 5

is the process by which two or more species evolve in response to selection pressures imposed by each other.

• Mutualism
• Commensalism
• Parasitism

Question 6

Mutualism

Answer 6

Both organisms in the interaction are interdependent on each other for resources or other services. As both organisms gain from the relationship, the interaction is (+/+)

Question 7

Commensalism

Answer 7

Only one of the organisms benefits (+/0)

Question 8

Parasitism

Answer 8

The parasite benefits in terms of energy or nutrients and the host is harmed as the result of the loss of these resources (+/-)

Question 9

Sexual reproduction - Costs and Benefits

Answer 9

• Costs:- males unable to produce offspring; only half of each parent’s genome passed onto offspring, disrupting successful parental genomes
• Benefits outweigh costs due to an increase in genetic variation in the population

Question 10

Asexual reproduction

Answer 10

Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats

Are not able to adapt easily to changes in their environment, but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur.

Question 11

Parthenogenes

Answer 11

Is is more common in cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity

Question 12

Meiosis

Answer 12

Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte. In diploid cells, chromosomes appear as homologous pairs

Question 13

What are Homologous chromosomes

Answer 13

• the same size
• same centromere position
• the same sequence of genes at the same loci

Question 14

Explain Meiosis I

Answer 14

• The chromosomes condense and the homologous chromosomes pair up
• Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged
• Linked genes are those on the same chromosome. -
• Crossing over can result in new combinations of the alleles of these genes
  Crossing over of DNA is random and produces genetically different recombinant chromosomes. Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
• Each pair of homologous chromosomes is positioned independently of the other pairs. This is known as independent assortment
• The chromosomes of each homologous pair are separated and move towards opposite poles.
• Cytokinesis occurs and two daughter cells form

Question 15

Explain Meiosis II

Answer 15

Cells undergoes a further division during which the sister chromatids of each chromosome are separated. A total of four haploid cells are produced.