O-LevelBiologyGenetics & Variation5090/22 · May/June 2020 · Q610 Marks
The diagram shows a magnified image of the chromosomes from one skin cell of a person. [Figure 6 (Magnified image of chromosomes from a skin cell, arranged in homologous pairs from 1 to 22, followed by X and Y sex chromosomes. Chromosome 21 appears to have three copies instead of two.)]
- (a)State two conclusions that can be made about this person using only information in the diagram and explain each conclusion.[5]
- (b)Name the type of gamete produced by a human male. Outline the process for producing this type of gamete.[5]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [1] male;
- [1] X + Y / non-matching sex chromosomes ;
- [1] Down's syndrome ;
- [1] 47 + not 46 (chromosomes);
- [1] three / extra + (chromosome) 21 ;
- [1] type of gamete: sperm;
- [1] process: testes;
- [1] meiosis / reduction division ;
- [1] chromosome number halved ;
- [1] haploid;
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