Inheritence

Question 1

Def of autosomal allele

Answer 1

All chromosomes except the X & Y

Question 2

Dihybrid cross

Answer 2

Inheritance of two genes at the same time

Question 3

Height and petal colour are controlled by separate genes on different chromosomes
Height gene: tall (T) and short (t)
Petal Colour: red (R) and white (r)
1) draw the possible gamete’s produced by heterozygous plant
2) show the results of crossing over 2 heterozygous plants
3) list the 4 possible phenotypes and the ratio they are found in of the offspring

Answer 3

1) possible gametes
TR Tr tR tr

2) draw a dihybrid cross with the 4 gamates on the top and the bottom.
(See notes for more info)

3) possible phenotypes
Tall & Red - TTRR , TTRr, TtRR, TtRr
Small & White - ttRr, ttRR
Tall & White - TTrr, Ttrr
Small & Red - ttrr

Ratio of phenotypes is 9:3:3:1

Question 4

Coat texture and colour are controlled by separate genes on different chromosomes
Texture : rough (R) and smooth (r)
Colour: black (B) and white (b)
1) show the results of crossing over a rough, black male (RrBb) and smooth,black female (rrBb)
2) list the 4 possible phenotypes and the ratio they are found in of the offspring

Answer 4

Males gamates= RB, Rb, rB, rb
Female gametes = rB, rb
1) Use dihybrid cross (see notes for more info)

2) rough, black - RrBB, RrBb
Rough, white - Rrbb
Smooth, black - rrBB, rrBb
Smooth white - rrbb

Ratio = 3:1:3:1

Question 5

Def of epistasis

Answer 5

Alleles of one gene are needed for expression of a second gene
(The relationship between genes where the allele of one gene affects the expression of different gene)

Question 6

Def of genotype

Answer 6

All the alleles that an organism carries on its chromosome

Question 7

Def of Phenotypes

Answer 7

Observable characteristics of an organism which result of the genotype as well as environmental factors

Question 8

Def of dominant allele

Answer 8

Only 1 allele is required for the characteristic to be expressed in the phenotype.

Question 9

Def of recessive

Answer 9

The characteristic is only expressed if there is no dominant allele present in order for the phenotype to be expressed

Question 10

Def of Codominant

Answer 10

Both alleles are expressed equally and contribute to the phenotype, with there being a blend of the 2 characteristics or both seen together

Question 11

Def of allele

Answer 11

An alternative form of a gene

Question 12

Def of locus

Answer 12

The specific position of the gene on the chromosome

Question 13

Def of monohybrid inheritance

Answer 13

When a phenotype or trait is controlled y a single gene

Question 14

Draw a monohybrid cross
E.g if the colour of peas
Is green (G) and yellow (g)
And parents are green homozygous
And yellow homozygous

Answer 14

See notes for cross
A ratio of 3:1 green: yellow

Question 15

Def of sex linkage alleles

Answer 15

The expression of an allele depends on the gender of the individual as the gene is located on a sex chromosome

Question 16

Def of autosomal linkage

Answer 16

Two or more genes are on the same autosomal chromosome.

autosomal - a gene that is not on the sex chromosomes

Question 17

Def of epistasis

Answer 17

When one gene locus affects the other gene locus

(One gene loci can either mask or suppress the expression off another gene locus)

Question 18

Recessive epistasis occurs when ….

Answer 18

The presence of a recessive allele prevents the expression of another allele at a second locus.

Recessive epistasis gives the ration 9:3:4

Question 19

Dominant epistasis occurs when …

Answer 19

A dominant allele at one locus completely masks the alleles at a second locus.

Dominant epistasis gives a ratio of 12:3:1

Question 20

How would you use X2 test to compare observed phenotypes and expected?

Question 21

Def of allele frequency

Answer 21

The number of times an allele appears within a population’s gene pool

Question 22

Def of gene pool

Answer 22

All the different variations of genes in individuals that make up a population

Question 23

Def of population

Answer 23

A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Question 24

What are the hardy-Weinberg laws

Answer 24

p +q =1

p^2 + 2pq + q^2 = 1

Where p = frequency of dominant allele
q = frequency of recessive allele
pq= frequency of heterozygous

Question 25

What is hardy-Weinberg principle

Answer 25

A mathematical model, which predicts that allele frequencies will not change from generation to generation

Question 26

What conditions must be met for Hardy-Weinberg principle to be true

Answer 26

1) population is large
2) mating is random
3) no mutations occur
4) no immigration or emigration of the population
5) all genotypes are equally fertile so that no natural selection takes place

Question 27

in genetic crosses, suggest why observed phenotypes are not the same as expected ratios
4 marks

Answer 27

1. Small sample size
2. Linked genes
3. Random fertilisation of gametes
4. Selectional advantages

Question 28

what is meant by term phenotype

Answer 28

The observable characteristics due to an individual’s genotype and environmental interactions

Question 29

What is genetic diversity

Answer 29

The measure of the variation of alleles within a population

Question 30

Def of gene pool and allele frequency

Answer 30

Gene pool = Total number of alleles in a given population
Allele frequency = number of alleles for a particular trait in a population

Question 31

outline evidence that suggests all modern humans are descended from a relatively small number of people

Answer 31

There is much less genetic variation within the human population than would be expected for a population of 8 billion

Question 32

*explain why this event is referred to as a genetic bottleneck

Answer 32

Genetic bottleneck means a large proportion of a population dies out leaving a small population with less genetic diversity (less variation/ fewer alleles)

Question 33

what is the founder effect

Answer 33

When a population is descended from a very small starting population following genetic bottleneck or migration to a new location

-this results in low genetic diversity

Question 34

Why is genetic diversity important in a population

Answer 34

Variation means there will always be some organism within population with ideal combination of alleles to survive and reproduce
- allows species to adapt to any environmental change
- ensure survival of species

Question 35

Def of speciation

Answer 35

The process by which new species arise after a population because separated and cannot interbreed

Question 36

Stages a population must go through to become a new species

Answer 36

1) reproductive isolation
a single population becomes divided and prevented from interbreeding
2) natural selection
different selection pressures act on each population causing new varieties each with slightly different alleles and phenotypes
3) genetic drift
over time each variety acquires different random mutations & chromosomes rearrangement = genetically distinct
4) speciation
each variety eventually becomes different species when they can no longer interbreed
5) change in allele frequency
Frequency of alleles changes, increasing if selected for and decreasing if selected against

Question 37

What are the 2 types of speciation

Answer 37

Allopathic speciation
- process of new species arising because of physical/geographic barrier separating them

Sympatric
- process of new species arsing when 2 populations within same area become reproductively isolated

Question 38

Def isolating mechanism

Answer 38

A factor that prevent varieties/ sub-populations from interbreeding

Question 39

Def of genetic drift

Answer 39

Variation in allele frequency of small populations due to chance/ random mutations and different selection pressures