Inheritance

Question 1

Key terms

Question 2

Define the term genotype.

Answer 2

The genetic constitution of an organism.

Question 3

Define the term phenotype.

Answer 3

Expression is due to the genotype and the environment.

Question 4

Define the term homozygous.

Answer 4

The alleles are both the same.

Question 5

Define the term heterozygous.

Answer 5

The alleles are different.

Question 6

Define the term recessive allele.

Answer 6

Only expressed if there are two copies present.

Question 7

Define the term dominant allele.

Answer 7

The allele is always expressed.

Question 8

Define the term codominant.

Answer 8

Both the alleles are expressed at the same time if there is one copy of each.

Question 9

Define the term multiple alleles.

Answer 9

The genes have more than two alleles.

Question 10

Define the term sex-linkange.

Answer 10

A gene whose locus is on the sex chromosomes.

Question 11

Monohybrid inheritance

Question 12

What is monohybrid inheritance?

Answer 12

The inheritance of a characteristic which is coded for by a single gene.

Question 13

Cystic fibrosis is caused by a recessive allele. If two carriers reproduce, what is the probability that their offspring will have cystic fibrosis? What is the probability their offspring will be a female with cystic fibrosis?

Answer 13

1. 25%
2. 12.5%

Question 14

Cows can be white, red or roan in colour. Red and white are both dominant. If two roan cows reproduce, what is the probability that they will have red offspring?

Answer 14

25%

Question 15

Parents with blood group A and blood group B reproduce. Ia and Ib are both dominant. What is the probability that their offspring will have blood group A?

Answer 15

25%

Question 16

Colour blindness is caused by a recessive allele found only on the X chromosome. If a non-colour-blind male reproduces with a female carrier of the allele, what is the probability that their offspring will be colour-blind?

Answer 16

25%

Question 17

Dihybrid crosses

Question 18

What is a dyhibrid cross?

Answer 18

The inheritance of two characteristics, that are controlled by different genes, at the same time

Question 19

What will be the ratio of phenotypes in a dihybrid cross of both the parents are heterozygous?

Answer 19

9:3:3:1

Question 20

Pea plants can be either yellow or green and they can either have a round or crinkled shape. The colour yellow and the round shape are both dominant. What will be the phenotypic ratio of the organs crossed that are heterozygous for both genes? Draw a diagram to expand this.

Answer 20

9:3:3:1

Question 21

Define the term epistasis.

Answer 21

Interaction of non-linked genes where one masks the expression of the other.

Question 22

Gene 1 controls whether pigment will be expressed in dogs. Allele E codes for pigment production, and Allele e codes for no pigment production, meaning the dogs will always be yellow. Gene 2 controls which pigment will be expressed. Allele B codes for black fur, and Allele b codes for brown fur. If two gods, which are heterozygous for both genes are crossed, what will be the phenotypic ratio?

Answer 22

9:4:3

Question 23

Sex-linkage

Question 24

What is a sex-linked gene?

Answer 24

A gene with a locus on the X chromosome.

Question 25

Explain why males are more likely to express a recessive X-linked allele.

Answer 25

1. Males only have one allele; this means it is always expressed. 2. Females have two alleles; this means they must have a homozygous recessive genotype for the recessive allele to be expressed.

Question 26

Autosomal linkage

Question 27

What is autosomal linkage?

Answer 27

1. The two genes are located on the same autosome. 2. These alleles are inherited together. 3. Crossing over can create new combinations of alleles, so the closer together the genes are, the less likely it is that they will be split by crossing over.

Question 28

In the cross between two peas that both have the genotype RrYy the possible phenotypes produced could be yellow and round peas, green and round peas, yellow and crinkled peas and green and crinkled peas. Explain why usually on yellow and round peas or green and wrinked peas are produced?

Answer 28

1. The RY and ry genes are linked. 2. This means RrYy parents mostly produce RY and ry gametes. This means the RRYY and rryy genotypes are more common in the offspring. 3. The gametes Ry and rY are formed due to crossing over, which is rare. 4. This means the RRyy and rrYY genotypes are less common.

Question 29

What test can be used to see if the difference between the expected results and observed results involving phenotype ratios is significant?

Answer 29

The chi-squared test.

Question 30

What is the formula for chi-squared?

Question 31

Why might the expected phenotypic ratios be different to the observed ratios?

Answer 31

1. Autosomal linkage, Sex-linkage, Epistasis, Random mutations. 2. There may be a lethal mutation that causes the organisms to die. 3. The sample size is too small to be representative of the whole population.

Question 32

What would be the null hypothesis is the chi-squared test? What are degrees of freedom in the chi-squared test?

Answer 32

1. That there is no significant difference between the expected ratios and observed ratios. 2. The number of phenotypes - 1

Question 33

What does it mean if the answer to the test is less than the critical value at a probabilty of 0.05?

Answer 33

p = 0.05 Degrees of freedom = number of phenotypes -1. If the value of chi-squared is less than the critical value then the difference is not significant.

Question 34

What does it mean if the answer to the test is greater than the critical value at a probabilty of 0.05?

Answer 34

p = 0.05 Degrees of freedom = number of phenotypes -1. If the value of chi-squared is greater than the critical value then the difference is significant.

Question 35

Why is the chi-squared test suitable for working with differences in phenotypes?

Answer 35

It uses categorical data.