Genetics_Long1

Give TWO reasons why cotton wool was used. (2)

To allow air to pass in and out/oxygen and carbon dioxide/gaseous exchange.

To prevent the fruit flies from escaping.

State ONE way in which the reliability of the results could be improved. (1)

Repeat the investigation.

Use a bigger sample/more flasks.

Use other organisms.

(Any 1)

Using the symbols R and r to represent the alleles for eye colour, state all the possible genotypes of the red-eyed fruit fly of the F2 offspring. (2)

RR ; Rr

As above, state all the possible genotypes of the white-eyed fruit fly of the F2 offspring. (1)

From the data, calculate the phenotypic ratio of the mice with black fur and the mice with brown fur in the F2 generation. (2)

24 : 8 (accept different correct working) = 3 : 1

Suggest why it is better to use the four sets of offspring to calculate the ratio rather than using only one set. (2)

To increase the reliability of the results. OR Reduces chances of errors.

Draw bar graphs on the same system of axes to represent the phenotypic results of the F2 generation offspring of each breeding pair shown in the table above. (9)

Answer

Give the ratio of the different phenotypes shown in the above table. (2)

1: 2: 1

Use the information in the table above to draw a pie-chart showing the proportions of the different genotypes. (7)

Answer

Explain why the cows and bulls with genotype RW have roan fur and not only red or only white fur. (3)

Both alleles for fur colour are equally dominant and therefore both are expressed in the phenotype. OR

Neither of the alleles for red or white colour are dominant over each other and therefore no one colour alone is expressed/masked in the phenotype/ both colours are expressed separately in different areas of the same animal.

By means of a diagram, show the genotypes that would be expected in the F1 generation. (10)

Answer

One of the white F1 offspring was crossed with its black parent. By means of a diagram, show the expected F2 genotypic results of this new cross. (12)

Answer

Show the genotypic results of this cross diagrammatically up to and including the F2 generation. (13)

Answer

What percentage of the F2 generation is homozygous for mottled leaves? (2)

25%

What type of dominance is being displayed? (1)

Incomplete Dominance

Using R for red flowers and W for white flowers, show the genotype of the F1 generation. (7)

Answer

If the F1 generation is crossed, show all the genotypes and phenotypes of the F2 generation. (7)

Answer

Draw schematic diagrams to show the genotypes of phenotypes of the F1 generation, and the genotypic and phenotypic ratios of the F2 generation. (15)

Answer

Set 1

Set 2

Set 3

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Question 1

Set 1

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A pure-breeding grey fly was crossed with a pure-breeding brown fly. All the offspring were brown. The F1 generation was then interbred.

Question 2

A farmer observes that black coat is dominant over white coat in the pigs that he owns. The farmer has a black, male pig whose genotype is unknown. Explain the easiest way for the farmer to determine the genotype of this male pig. Show all working and set out your answer clearly. (20)

Question 3

A red flowering plant was crossed with a white flowering plant and the F1 generation had all pink flowers.

Question 4

A plant homozygous for green leaves (G) is crossed with a plant homozygous for mottled leaves (g). The F1 generation is green leafed.

Question 5

In guinea-pigs, the gene for black coat is dominant to the gene for white-coat. Two heterozygous black guinea-pigs are crossed.

Question 6

In an experiment to show co-dominance, cows with white fur (W) were crossed with bulls with red fur (R). All the offspring of the F1-generation have roan fur (RW). A roan fur consists of patches of white and patches of red fur. Roan cows and roan bulls were crossed and the results are shown in the table below.

Question 7

The table below shows the results obtained by first crossing a pure-bred black furred mouse with a brown furred mouse. The gene for black fur is dominant over the gene for brown fur. The F1 generation was used as parents (consisting of 4 breeding pairs) of the F2 generation.

Question 8

An investigation was conducted by grade 12 learners on fruit flies to determine the genotypic and phenotypic ratios of the F2 generation. They placed 12 homozygous red-eyed females in a flask with 12 homozygous white-eyed males. The flask contained a ripe fruit and the opening of the flask was covered with cotton wool. After three weeks the F1 offspring were crossed and the results (F2) are shown in the table below.

Draw schematic diagrams to show the genotypes of phenotypes of the F1 generation, and the genotypic and phenotypic ratios of the F2 generation. (15)

Answer

- Monohybrid Crosses -

Set 5

Questions source: DBE (Authorisation 11798)

- Greg Gopaul -