Inheritance

Question 1

Phenotype

Answer 1

Expression of genetic constitution / genotype / allele(s);

AND its interaction with the environment;

Question 2

Dominant allele

Answer 2

Is always expressed / shown
in the phenotype;

Question 3

Recessive allele

Answer 3

Requires both alleles to be present - homozygous recessive genotype - to be expressed / show in the phenotype.

Question 4

Genotype

Answer 4

The genetic constitution of an organism.

In other words, all the alleles it contains

e.g. Heterozygous OR homozygous recessive

Question 5

Define a gene

Answer 5

A sequence of DNA bases that codes for a protein

Question 6

(AO1)

Define an allele

Answer 6

Different versions of the same gene

These are typically created by random mutations

Question 7

There may be many _____________ of a single gene.

Answer 7

alleles

Question 8

In a diploid organism, the alleles at a specific __________ may be either homozygous or heterozygous.

Answer 8

locus

Question 9

Define locus

Answer 9

a
The location/position of a particular gene on a chromosome

Question 10

If there the two copies of a gene are the same allele in a genotype, this is known as __________________

Answer 10

homozygous

Question 11

If there the two copies of a gene are different alleles in a genotype, this is known as __________________

Answer 11

heterozygous

Question 12

What is the expected phenotypic ratio if your cross heterozygous parents (i.e. they carry the recessive allele) in a monohybrid cross?

Answer 12

3 : 1

Where 1 represents the phenotype from the homozygous recessive genotype

Question 13

A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.

Explain the evidence that the allele for white fur is recessive.

Answer 13

Parents are heterozygous;

Accept carriers / carries white allele

Kittens receive white allele from parents / black cat;

Question 14

A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.

Predict the likely ratio of colours of kittens born to a cross between this black male and a white female.

Answer 14

1:1

A Bb (Black) x bb (White) cross will produce Bb and bb offspring

Question 15

In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g.

Explain how you would determine if the genotype of a grey is homozygous or heterozygous for body colour (2 marks).

Answer 15

1. Cross with a homozygous recessive black fly (with the gg genotype)
2. If some offspring are black, then must be heterozygous/Gg

OR if all offspring are grey, then must be homozygous/GG

Question 16

What is the expected phenotypic ratio if your cross heterozygous parents for a codominant phenotype.

Answer 16

1 : 2 : 1

Question 17

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

Answer 17

Small sample size;
Fusion / fertilisation of gametes is random;
Linked genes;
Epistasis;
Lethal genotypes;

Question 18

Gametes produced by AaBb genotype.

The genes are on different chromosomes.

Answer 18

AB , Ab , aB , ab

Question 19

Expected phenotypic ratio of offspring if both parents are heterozygous in a dihybrid cross.

i.e. AaBb x AaBb

Answer 19

9 : 3 : 3 : 1

Question 20

Mutation is one cause of genetic variation in organisms.

Give two other causes of genetic variation.

Answer 20

1. Crossing over;
2. Independent segregation
   (of homologous chromosomes);
3. Random fusion of gametes

OR random fertilisation;

Question 21

What process during meiosis 1 creates different combinations of alleles in the gametes?

Answer 21

Independent segregation

Question 22

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (6 marks).

Answer 22

(Crossing over)
1. Homologous chromosomes pair up / bivalents form;

2. Crossing over / chiasmata form;
3. Produces new combination of alleles;
   (Independent segregation)
4. Homologous chromosomes separate;
5. At random;
6. Produces varying combinations of chromosomes / genes / alleles;
7. Sister chromatids separated at meiosis II;

Question 23

Which process during meiosis 1 produces recombinant gametes?

a

Answer 23

crossing over

Question 24

How could you prove a dominant allele is NOT sex-linked?

Explain why.

CLUE = mums & sons

Answer 24

If the allele is sex-linked, homozygous recessive mothers will always have sons that show the recessive phenotype.

If, however, the sons show a dominant phenotype, there is no way he could have inherited this on the X chromosome from his mother.

The dominant allele must be on another chromosome.

Question 25

When to use the chi squared test?

Answer 25

To test if there is a significant difference between the observed AND expected numbers in an investigation with categorical data

Question 26

Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results?

Give the reason for your choice of statistical test.

Answer 26

Chi squared test;
Categorical data.

Question 27

When using the chi squared test, how do you calculate the degrees of freedom?

Answer 27

n - 1

Where ‘n’ represents the number of categories / groups / phenotypes

Question 28

There are 4 possible phenotypes with expected and observed results, calculate the degrees of freedom?

Answer 28

3

As degrees of freedom = n - 1

(where n represents the number of categories / phenotypes)