6.2: Patterns of inheritance

Question 1

The frogs in show discontinuous variation in colour. Suggest:
one other phenotypic characteristic in which the frogs show a discontinuous pattern of variation.
one phenotypic characteristic in which they show a continuous pattern of variation. f215 june 14 q1ai

Answer 1

discontinuous:
gender / male and female / eye colour;
continuous:
size / length / mass / surface area

Question 2

State the extent to which the environment is likely to affect phenotypic characteristics. (2mks) f215 june 14 q1aii

Answer 2

1 no / little, environmental effect for discontinuous variation [disc. var. is only, genetic/ due to alleles present]
2 some / large, environmental effect for, cont. var.
3 gender may be affected by, temperature/ atrazine exposure [(e.g. ‘ environment has a greatER effect on continuous variation’) = 2 marks; e.g ‘ no environment effect for discontinuous variation but it does affect continuous variation’ = 2 marks]

Question 3

Three adult frogs (A,B andC)that were used to create them.
• frog A, a brown-coloured female frog, laid eggs, which then had their nuclei removed.
• frog B, an albino (white-coloured) female, laid eggs that were fertilised by sperm from C.
• frog C, an albino male, produced sperm that fertilised the eggs of B.
One of the fertilised eggs from B was allowed to divide. Nuclei were extracted from the resulting
cells and placed into the eggs from frog A. These eggs developed into the frogs labelled
D in Fig. 1.1.
Suggest why albino frogs were used to produce the nuclei for transfer. (2mks)
[f215-01 jun14 q1aiii]

Answer 3

1 offspring visibly different from, A / egg donor;
2 to show that the offspring produced were clones;
3 to show/ identify, (genetic) parents (of clone)/ B and C;
[To show that the offspring were clones as they are
not the same as A.’ = 2 marks]

Question 4

Mitochondrial DNA from the frogs was sequenced.
State, giving a reason, which of the frogs A, B and C would have a mitochondrial DNA sequence identical to D. f215 june 14 q1bii

Answer 4

ref to frog A; cytoplasm / mitochondria, came from A

or mitochondria / (mitochondrial) DNA, in cytoplasm of A

Question 5

Give two reasons why it was not appropriate to use the Hardy-Weinberg principle to estimate the frequencies of alleles in this group of rabbits in the pet shop. f215 june 14 q6bii

Answer 5

in the pet shop:
1 population is , small / not (sufficiently) large ;
2 not all members of the population are breeding ;
3 idea that mating is not random ;
4 idea that migration / emigration / immigration ,
is occurring ;
5 idea that the non-brown rabbits could be colours
other than white
[IGNORE ref to (natural) selection / mutation (as these do not apply to the ‘artificial’ population in the pet shop) IGNORE ‘albinos are infertile’]