Unit 3.4.8 - Genetic Variation

Question 1

What is a gene?

Answer 1

A sequence of bases on a DNA molecule that codes a protein which results in a characteristic.

Question 2

What are alleles?

Answer 2

Different version of the same gene, one from each parent.

Question 3

Where is the allele of each gene found?

Answer 3

On a fixed position called a locus on each chromosome pair.

Question 4

What is a genotype?

Answer 4

The genetic constitution of an organism, the allele combination.

Question 5

What is a phenotype?

Answer 5

The expression of the genotype and it’s interaction with the environment.

Question 6

What is a dominant allele?

Answer 6

An allele whose characteristic appears in the phenotype when there is only one copy.

Question 7

What is a recessive allele?

Answer 7

A characteristic that only appears in the phenotype if there are two copies present.

Question 8

What are co dominant alleles?

Answer 8

When neither one of the alleles is recessive or dominant so the heterozygous has a intermediate phenotype, both alleles are represented.

Question 9

What is homozygous?

Answer 9

When an organism carries two copies of the same allele.

Question 10

What is Heterozygous?

Answer 10

When an organism carries two different alleles.

Question 11

What do genetic diagrams show?

Answer 11

The possible genotypes of offspring, so they can be used to predict the genotypes and phenotypes of offspring.

Question 12

What do mono hybrid crosses and punnet squares show?

Answer 12

The likelihood of alleles being inherited by offspring from particular parents.

Question 13

What does it mean if characteristics are sex linked?

Answer 13

The alleles that code them are located on the sex chromosome.

Question 14

Give 2 examples of sex linked characteristics.

Answer 14

1. Colourblindness

2. Haeomophilia

Question 15

Give an example of a characteristic that is caused by co-dominant alleles.

Answer 15

Blood type.

Question 16

What do genetic pedigree diagrams show?

Answer 16

How an inherited trait runs in a group of related individuals.

Question 17

From a pedigree diagram how can you see that a disease is recessive?

Answer 17

Unaffected parents will have affected children.

Question 18

From a pedigree diagram how can you see that an allele is carried on a sex chromosome?

Answer 18

Affected dad has unaffected daughter

Question 19

What is a species?

Answer 19

A group of similar organisms that can reproduce to give fertile offspring.

Question 20

What is a population?

Answer 20

A group of organisms in the same species living in a particular area.

Question 21

What is the gene pool?

Answer 21

The complete range of alleles present in a population.

Question 22

What is an allele frequency?

Answer 22

How often an allele appears in a population.

Question 23

What is the Hardy Weinberg principle?

Answer 23

A mathematical model that predicts the frequency of alleles in a population that won’t change from one generation to the next.

Question 24

What are 6 conditions for the Hardy Weinberg principle to apply?

Answer 24

1, Large population

2. No migration
3. No mutations
4. No natural selection
5. Random mating

Question 25

What can the Hardy Weinberg equations be used to predict?

Answer 25

Frequency of particular alleles and genotype within the populations and whether the Hardy Weingberg principle applies.

Question 26

What equation shows the allele frequencies?

Answer 26

p + q = 1

Question 27

What does p stand for?

Answer 27

Frequency of the dominant allele.

Question 28

What does q stand fod?

Answer 28

Frequency of the recessive allele.

Question 29

What equation shows the genotype frequencies?

Answer 29

p² + 2pq + q² = 1

Question 30

p²

Answer 30

Frequency of homozygous dominant genotype.

Question 31

What does 2pq stand for?

Answer 31

Frequency of heterozygous genotype

Question 32

q²

Answer 32

Frequency of homozygous recessive genotype.

Question 33

What does the Hardy Weinberg principle predict?

Answer 33

The frequency of alleles within a population wont change from one generation to the next so if you see the allele frequency has changed then the principle doesn’t apply and there must be factors affecting the allele frequency.

Question 34

What is differential reproductive success?

Answer 34

When individuals have an allele that increases their chances of survival they are more likely to survive reproduce and pass on their genes than individuals with different alleles

Question 35

What is natural selection?

Answer 35

When individuals have an allele that increases their chances of survival they are more likely to survive reproduce and pass on their genes than individuals with different alleles, this means a greater proportion of the next generation will inherit the beneficial all and so the frequency of the beneficial allele increases

Question 36

What are the three types of selection?

Answer 36

Stabilising selection, directional selection, disruptive selection

Question 37

How does stabilising selection act?

Answer 37

Acts to keep the phenotype the same

Question 38

When stabilising selection occur?

Answer 38

When the environment isn’t changing

Question 39

What happens during stabilising selection?

Answer 39

Selection pressures act on the individuals that are at the extremes of the range because they are less well adapted. Individuals with a phenotype closest to the optimum are the best adapted and so are more likely to survive and reproduce

Question 40

What does stabilising do to the range of possible phenotypes?

Answer 40

Reduces the range

Question 41

How does directional selection act?

Answer 41

Acts to alter the phenotype when the environment is changing

Question 42

What happens during directional selection?

Answer 42

The environment might change and so the original optimum phenotype may no longer be the optimum.
Selection pressures acts on those phenotypes furthest away from the new optimum.
Over several generations the distribution shifts and a new optimum is established

Question 43

How does disruptive selection act?

Answer 43

Acts in the favour of the two extremes of the range of phenotypes and eventually the middle of the range disappears

Question 44

When does disruptive selection occur?

Answer 44

When the population is exposed to two different environments

Question 45

What are the two main causing of isolation?

Answer 45

Migration and geographical isolation

Question 46

How can migration lead to the formation of a new gene pool?

Answer 46

Over-crowding means some of the population might move to another environment forming another new gene pool

Question 47

How can geographical isolation lead to the formation of a new gene pool?

Answer 47

A physical barrier like a flood, earthquake or volcanic eruption can separate populations forming a new gene pool

Question 48

How does isolation cause speciation in 6 steps?

Answer 48

1. Populations that are isolated so there will be two gene pools which will experience different environments
2. Mutations cause variation
3. Different mutations will be more beneficial and so selection (directional) begins to work differently on the two populations
4. The populations will start to become different from each other
5. Over time reproductive isolation occurs, this happens when the organisms are unable to court each other or mate with each other or produce fertile offspring
6. And so will have become separate species