genetics sample exams questions and answers

Question 1

What is a section of DNA that codes for a protein called?

Answer 1

Gene

Question 2

Explain why Mendel’s work was not recognised when he first published.[2 marks]

Answer 2

Two from:

• when he presented his work to other scientists he did not communicate it well so they did not really understand it
• it was published in a scientific journal that was not well known so not many people read it
• he could not explain the science behind why characteristics were inherited

Question 3

Describe the difference between genotypes and phenotypes? Give an example of each in your answer. [4 marks]

Answer 3

• genotypes are letters used to determine characteristics
• BB, Bb, bb for eye colour (accept other suitable examples)
• phenotypes are physical descriptions using words that describe genotypes
• so BB and Bb are brown eyes and bb is blue eyes (accept other suitable examples)

Question 4

State what gamma rays, X-rays and ultraviolet rays are? [1 mark]

Answer 4

Types of ionising radiation

Question 5

Explain what was interesting about the results of Mendel’s famous second cross between red pea plants from the initial first cross of red and white pea plants? Include the percentages of the colours in your answer. [4 marks]

Answer 5

• 25% of the plants were white
• 75% were red
• this proved red is dominant over white
• it also proves that heterozygous red plants have the allele for white within them [1 mark] even though it is not expressed [1 mark].

Question 6

Explain how inheritance of biological sex occurs in humans. [4 marks]

Answer 6

• all ova are X
• half of sperm are X [1 mark] and half are Y [1 mark]
• a baby with genotype XX is female
• a baby with genotype XY is male

Question 7

One quarter of Mendel’s peas in his famous second cross were white and three quarters were red. What is this as a ratio? [1 mark]

Answer 7

1:3

Question 8

Of the world’s population, 47% are blood group O. Calculate the proportion of the world that has a different blood group? [1 mark]

Answer 8

0.53

Question 9

Describe the process of selective breeding. Give examples in your answer. Analyse your results in terms of percentages. [6 marks]

Answer 9

• decide which characteristics are important enough to select
• choose parents that show these characteristics from a mixed population - they are bred together
• choose the best offspring with the desired characteristics to produce the next generation
• repeat the process continuously over many generations, until all offspring show the desired characteristics
• examples of animals: pigs, sheep, cows, dogs or other suitable examples
• examples of plants: broccoli, Brussel sprouts, cabbage, cauliflower

Question 10

Describe the role of mutations in evolution. [4 marks]

Answer 10

Answer (four from):

• a mutation is a change to a gene or chromosome
• it can have an advantage, disadvantage or no effect
• advantageous mutations make individual organisms better adapted
• they are therefore more likely to survive (survival of the fittest)
• they are more likely to reproduce
• their offspring are more likely to have this advantage

Question 11

Compare and contrast sexual and asexual reproduction. [4 marks]

Answer 11

Answer (four from):

• sexual reproduction involves two parents [1 mark] and produces genetically different offspring [1 mark]
• asexual reproduction involves one parent [1 mark] and produces genetically identical offspring [1 mark]
• asexual reproduction is called cloning and produces clones
• plants (and other named species) can reproduce sexually and asexually
• taking plant cuttings is an artificial form of asexual reproduction
• tissue culture in plants is an artificial form asexual reproduction
• embryo transfer in animals is an artificial form asexual reproduction
• cloning in animals is an artificial form asexual reproduction
• asexual reproduction is generally faster [1 mark] but produces offspring with less variation [1 mark]
• sexual reproduction is generally slower [1 mark] but produces offspring with more variation [1 mark]

Question 12

Describe how mutations in DNA are caused and explain their possible effects. [5 marks]

Answer 12

Answer (five from):

• mutations are changes in the DNA sequence of an organism
• they can be insertion, deletion, substitution or inversion of base pairs (up to four marks if explained)
• this can be advantageous [1 mark], disadvantageous [1 mark], or have no effect [1 mark]
• mutations are caused at random, or by ionising radiation and mutagenic chemicals (carcinogens)
• rapid cell growth of mutated cells can form cancerous tumours
• benign tumours grow slowly [1 mark], are easily removed [1 mark] and do not invade other parts of the body [1 mark]
• malignant tumours grow rapidly [1 mark], are more difficult to remove [1 mark] and do invade other parts of the body [1 mark]