GeneticsEdexcel GCSE Biology: Topic test

20 questions, 54 marks

Edexcel GCSE Biology

Genetics topic test

Total 54 marks

Name

Class

Date

1
A zoo keeps a single female Komodo dragon in an enclosure with no males present. Unexpectedly, she lays a clutch of eggs that hatch successfully into healthy young Komodo dragons, all of which are genetically very similar to their mother and to each other.
(a)
What type of reproduction is most likely to have produced this clutch of eggs?
[1 mark]
AAsexual reproduction
BSexual reproduction
CVegetative propagation of plant tissue
DBinary fission
(b)
What is one disadvantage, shown by this event, of asexual reproduction compared with sexual reproduction?
[1 mark]
AIt requires more energy than sexual reproduction
BOffspring show very little genetic variation from their mother or each other, making the population more vulnerable if the environment changes
CIt always produces fewer offspring than sexual reproduction
DIt cannot occur in reptiles under normal circumstances
(c)
Explain why the offspring produced this way show so little genetic variation from their mother.
[2 marks]
Total for question 1: 4 marks
2
A student extracts DNA from a banana using simple laboratory equipment: mashing the fruit, adding a salt-detergent solution to break open cells, filtering the mixture, and finally adding ice-cold ethanol, which causes visible white strands of DNA to precipitate out of solution.
(a)
What is the main role of the detergent added during the DNA extraction?
[1 mark]
AIt provides energy for the DNA to move
BIt colours the DNA so it can be seen
CIt breaks down the cell membranes (and nuclear membrane), releasing the DNA into solution
DIt amplifies (copies) the DNA many times
(b)
Which statement correctly describes the structure of the DNA that precipitates out of the solution?
[1 mark]
AA single strand of nucleotides folded into a sphere
BA single circular loop of DNA, as found in a bacterial cell
CA single strand of amino acids
DTwo strands of nucleotides coiled together to form a double helix, linked by complementary base pairs
(c)
Explain why adding ice-cold ethanol to the filtered mixture makes the DNA visible as white strands.
[2 marks]
Total for question 2: 4 marks
3
Two parents, neither of whom has albinism, have a child born with albinism, a condition caused by a recessive allele (a) that prevents the production of the pigment melanin. The dominant allele (A) allows normal melanin production.
(a)
Explain what the genotypes of the two parents must be, and explain why neither parent shows albinism themselves.
[3 marks]
(b)
Using the parents' genotypes, calculate the probability that a second child born to this couple will have albinism. Show your working.
[4 marks]
Total for question 3: 7 marks
4
A female dog and a male dog produce a litter of six puppies. Even though all six puppies have the same two parents, they show a range of different coat colours and patterns from one another, and none is genetically identical to either parent. Two of the puppies, born with identical coat colour genes, are then raised in very different environments: one lives mostly outdoors and develops a thicker, darker coat, while the other lives mostly indoors and keeps a thinner, lighter coat.
(a)
Explain, in terms of meiosis, why the puppies in this litter are not genetically identical to each other or to either parent.
[6 marks]
(b)
Explain why the two puppies with identical coat colour genes can still look different from each other, and explain why this kind of difference would not be passed on to the puppies' own offspring in the same way that genetic variation would be.
[6 marks]
Total for question 4: 12 marks
5
A biology textbook states that in humans, meiosis in the testes produces four sperm cells from each parent (diploid) cell that undergoes division. Each of the four sperm cells produced from the same parent cell carries a different combination of alleles.
(a)
How many daughter cells does meiosis produce from one parent cell?
[1 mark]
ATwo
BFour
CEight
DOne
(b)
What is the chromosome number of each of the four sperm cells compared with the original parent cell?
[1 mark]
AHalf the number (haploid)
BThe same number (diploid)
CDouble the number
DA random, unpredictable number
(c)
Explain why the four sperm cells produced from the same parent cell are genetically different from one another, even though they all came from the same original cell.
[2 marks]
Total for question 5: 4 marks
6
A couple are expecting a baby and want to understand how the baby's biological sex will be determined. A genetic counsellor explains that, in humans, egg cells always carry an X chromosome, but sperm cells can carry either an X chromosome or a Y chromosome, in roughly equal proportions.
(a)
Which combination of sex chromosomes in the fertilised egg (zygote) would result in a male baby?
[1 mark]
AXX
BYY
CXO
DXY
(b)
Since egg cells always carry an X chromosome, which parent's gamete determines the biological sex of the baby?
[1 mark]
ABoth parents equally and unpredictably
BNeither - sex is determined randomly after fertilisation
CThe father's sperm cell
DThe mother's egg cell
(c)
Explain why approximately equal numbers of male and female babies are born in a large population, referring to the sperm cells produced by meiosis.
[2 marks]
Total for question 6: 4 marks
7
A mutation occurs in the coding DNA of a gene that codes for a particular enzyme. The mutation changes just one base in the DNA sequence, which changes the amino acid sequence of the protein produced. As a result, the enzyme's active site is a slightly different shape from normal, and the enzyme now works far more slowly than the normal version.
(a)
Explain the sequence of effects, from the change in a DNA base to the change in the enzyme's shape.
[3 marks]
(b)
Explain why this change in the enzyme's active site shape causes it to work more slowly, and explain why some mutations, unlike this one, have no effect at all on an organism's phenotype.
[4 marks]
Total for question 7: 7 marks
8
The Human Genome Project mapped the entire sequence of human DNA and showed that, although any two unrelated people share about 99.9% of their DNA sequence, there are still millions of small differences between individuals across the population, thought to have arisen through mutation and through the shuffling of alleles that happens during sexual reproduction.
(a)
Explain how meiosis, combined with sexual reproduction, contributes to the genetic differences between unrelated individuals described by the Human Genome Project, in addition to the role of mutations.
[6 marks]
(b)
Discuss one potential medical application of the detailed knowledge of human genes and genetic variants produced by the Human Genome Project, and evaluate one potential concern this raises.
[6 marks]
Total for question 8: 12 marks

End of questions