Module 6: Genetics and evolution

Question 1

Types of gene mutation

Answer 1

Substitution = a nucleotide base is replaced with another
Insertion = an extra nucleotide base is inserted into the sequence causing ‘frameshift’ where all the subsequent bases are shifted down 1 place relative to the twin DNA strand
Deletion = the absence of a nucleotide, causing ‘frameshift’ where all the subsequent bases are shifted back 1 place relative to the twin DNA strand

Question 2

Effects of mutations on proteins

Answer 2

Harmful
May result in change in final protein shape where protein and active site is deformed and therefore cannot fulfil function
Beneficial
May result in change in final protein shape where the protein performs its function better than it would have without the mutation
Neutral
As most amino acids have two or more codons, mutation can be neutral

Question 3

What are homeobox genes

Answer 3

Genes that turn on/off development of specific body parts and is found within many genes
They are grouped together as homeotic genes in a ‘hox cluster’ more complex organisms have more hox clusters Homeobox genes expressed in specific patterns in certain stages of development activated and expressed from anterior to posterior which is very similar across species and highly conserved- Indication that they first arose in early common ancestor

Question 4

Sequence of events in Apoptosis

Answer 4

1. Enzymes break down the cytoskeleton which causes bulges in the plasma membrane (blebs)
2. cell breaks down into vesicles called apoptotic bodies
3. Phagocytosis of apoptotic fragments by phagocytes

Question 5

Linkage

Answer 5

When two or more genes are located on the same chromosome

Question 6

Codominance

Answer 6

when both alleles present in the genotype contribute to the phenotype.

Question 7

Epistasis

Answer 7

interaction of non-linked genes which affects the expression of the other.

Question 8

Difference between continuous and dis-continuous variation

Answer 8

Continuous variation
Phenotypes fall in a range
Smooth gradient between phenotypes, which are often distributed in a bell curve
Eg tail length in mice; birth weight; height; skin colour; heart
Discontinuous variation
Phenotypes are in distinct categories
E.g. blood types or sex

Question 9

Evolution of a species

Answer 9

Genetic drift- Occurs when population is small to begin with meaning it has a small gene pool
The isolated population can ‘drift’ and become very different to the parent population
Genetic bottleneck- When a population shrinks and then increases again E.g. when disease spreads through a population and few survive
The new population has reduced genetic diversity as their genes derive from a few individuals
Founder effect- If a new population is established from very few ‘founding’ individuals, there will be little genetic diversity and a small gene pool

Question 10

Isolating mechanisms

Answer 10

Geographical isolation
2 groups separated geographically Eg. ocean/mountains/rivers
2 groups do not meet and cannot interbreed
Reproductive isolation
Biological/behavioural changes arise from mutation
Mutation only affects some individuals in the species population e.g. mutation causes individuals to become active at night rather than in the day
Changes foraging behaviour
These individuals only meet/breed with individuals also active at night

Question 11

Artificial selection

Answer 11

farmers and breeders select individuals from a population with desirable traits - e.g. cereal with resistance to drought, or cows with high milk yields.
Ethics
Reduces genetic variation
susceptible to diseases