13.6 Inheritance

Question 1

P + q =

Answer 1

1

Question 2

What does Hardy Weinberg equation predict? [3]

Answer 2

• The frequency of alleles (of a particular gene);
• Will stay constant from one generation to the next/over generations;
• Providing (2 from the following) no mutation/no selection/population large/population genetically isolated/mating at random/no migration;

Question 3

What is the Hardy-Weinberg phenotype equation?

Answer 3

Question 4

What should the allele frequencies add up to?

Answer 4

1

P + q = 1

Question 5

In the HW principle, what represents the following:

1: Dominant allele frequency
2: recessive allele frequency
3: proportion of heterozygote phenotypes (within population)
4: proportion of homozygous recessive phenotypes (within population)

Answer 5

1: P
2: q
3: 2Pq
4: q squared

Question 6

Suggest why the sum of allele frequencies could be greater than 1.

Answer 6

More than one gene affects the expression of the phenotype.

(Alleles of more than one gene)

Question 7

What is meant by a genome?

Answer 7

• (All) the DNA in a cell/organism;
• (all) the genes/alleles/genetic material/code in a cell/organism/ person
• the total number of DNA bases in a cell/organism

Question 8

State three causes of genetic variation [3]

Answer 8

• Mutation
• Crossing over
• Independent segregation (of homologous chromosomes)
• Random fusion of gametes / fertilisation / mating
• Produces new combinations of alleles.

Question 9

Explain how a single base substitution causes a change in the structure of a polypeptide [3]

Answer 9

• Change in (sequence of) amino acid(s) / primary structure;
• Change in position of hydrogen/ionic/disulfide bonds;
• Alters tertiary structure;
• No longer complementary / unable to bind to target molecule.

Question 10

What is meant by the term Genotype?

Answer 10

• The genetic constitution of an organism.
  *Or
• All the alleles an organism has

Question 11

What is meant by the term phenotype [2]

Answer 11

• Expression of genetic constitution / genotype / allele(s);
• interaction with environment;

Question 12

What is meant by the term dominant allele?

Answer 12

Always expressed within the phenotype.
(even when heterozygous)

Question 13

What is meant by a recessive allele?

Answer 13

• Only expressed when homozygous / not expressed in the heterozygote / not expressed if dominant present;

Question 14

State the rules for dominant alleles. [3]

Answer 14

• Affected offspring MUST have at least one affected parent.
• Unaffected parents ONLY have unaffected offspring.
• If both parents are affected and have an unaffected offspring, both parents must be Heterozygous

Question 15

State the rules for recessive alleles. [1]

Answer 15

• Unaffected parents can have an affected offspring (if they are Heterozygous)

Question 16

Define codominance

Answer 16

• Both alleles (equally) expressed within the phenotype;

Question 17

How do multiple alleles of a gene arise?

Answer 17

• mutations;
• which are different / at different positions within the gene;

Question 18

Define epistasis

Answer 18

• The expression of one gene alters/affects the expression of another gene within the phenotype.

Question 19

Define (Autosomal) gene linkage

Answer 19

Genes are on the same homologous pair of chromosomes (not the sex chomosomes)

Question 20

Independent segregation is:

Random or Rare?

Answer 20

RANDOM

All possible allele combinations are produced in equal numbers

Question 21

Crossing over is:

Random or Rare?

Answer 21

RARE

Only occurs between homologous chromosomes

If genes are linked…. new recombinant allele gametes are produced in very low numbers.

Question 22

An organism has the following genotype, the genes are linked.

AaBb

Assuming no crossing over takes place (as this is a rare process), what are the gamete genotypes produced.

Answer 22

AB & ab in equal numbers.

*Crossing over could produce fewer Ab & aB gametes.

Question 23

What are the Expected offspring phenotype ratios from heterozygous parents:

1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage

Answer 23

1. 3:1
2. 9:3:3:1
3. 9:4:3 or 15:1 or 9:7
4. 3:1 (if no crosiing over) (no other pattern other than 4 phenotypes and recombination of alleles being the fewest)

Question 24

Define Sex linkage

Answer 24

• The expression of an allele dependant on the gender of the individual as the gene is located on the sex chromosomes. (X chromosome)

Question 25

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why. [2]

Answer 25

* (Recessive) allele is always expressed in males / males have one (recessive) allele; * Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;

Question 26

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 26

* Small sample size; * Fusion/fertilisation of gametes is random; * Linked Genes / Sex-linkage / crossing over; * Epistasis; * Lethal genotypes/allele combinations;

Question 27

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 fly is homozygous or heterozygous for body colour. [2]

Answer 27

1. Cross with homozygous recessive (fly) OR Cross with a black (fly) OR Cross with gg (fly); Accept cross with heterozygous (fly) 2. Black offspring/flies then is heterozygous/Gg OR Black and grey offspring/flies then is heterozygous/Gg OR No black offspring/flies then is homozygous/GG OR All grey offspring/flies then is homozygous/GG;

Question 28

In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r. Male fruit flies are more likely than female fruit flies to have white eyes. Explain why. [2]

Answer 28

1. Males have one / only need 1 allele; 2. Females need two recessive alleles **OR** Females must be homozygous recessive **OR** Females could have dominant and recessive alleles **OR** Females could be heterozygous/carriers;

Question 29

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 29

1. Small sample size; 2. Fusion/fertilisation of gametes is random; Ignore breeding is random 3. Linked Genes; Accept crossing over / sex linkage 4. Epistasis; 5. Lethal genotypes;

Question 30

1: Suggest **two** reasons why observed ratios are often not the same as expected ratios. **AND** 2: A student wished to test her results with the ones she had expected. Which statistical test should she use?

Answer 30

Fertilisation is random OR Fusion of gametes is random; 2. Small / not large population / sample; 3. Selection advantage / disadvantage / lethal alleles; 2: **χ2 / chi squared;**

Question 31

There were 850 fruit flies in one population. In this population, 510 fruit flies had the genotype NN, 255 had the genotype NV and 85 had the genotype V V. Calculate the actual frequency of the allele V. Do **not** use the Hardy-Weinberg equation in your calculation.

Answer 31

(85 X 2) + 255 = 425 425 / 1700 0.25

Question 32

In fruit flies, the genes for body colour and wing length are linked. Explain what this means.

Answer 32

(Genes / loci) on same chromosome.

Question 33

Define 'homozygous'

Answer 33

2 of the same alleles (of a gene) AA or aa BB or bb

Question 34

Define 'heterozygous'

Answer 34

two different alleles (of the same gene) Aa or Bb

Question 35

Define the following genotypes: 1. AA 2. aa 3. AaBb

Answer 35

1. Homozygous dominant (gene A) 2. Homozygous recessive (gene A) 3. Heterozygous for gene A & B

Question 36

List the gamete genotypes (allele combinations) for the following parental genotypes: Aa

Answer 36

A AND a

Question 37

List the gamete genotypes (allele combinations) for the following parental genotypes: AA

Answer 37

All / 100% of gametes will be A (only)

Question 38

List the gamete genotypes (allele combinations) for the following parental genotypes: AABb

Answer 38

AB & Ab only

Question 39

List the gamete genotypes (allele combinations) for the following parental genotypes: AaBb

Answer 39

AB Ab aB ab

Question 40

When would you use the Chi squared test?

Answer 40

* Categoric data * To determine if there is a significant difference between observed and expected ratios.

Question 41

What causes variation in **phenotypes** within a population?

Answer 41

Genetic and environmental factors.