2019HSCShort answer

Q25 (b)

4 marks

Question

A human karyotype that shows evidence of chromosomal mutation is shown.

Explain how cell division and fertilisation could lead to the production of this karyotype.

Uncropped source page 17 for question 25.b; requires human review and cropping — Reviewed visual · source page 17

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Solution

Criteria	Marks
Explains how meiosis can lead to the karyotype<br>Explains how fertilisation can lead to the karyotype	4
Relates a problem during separation of chromosomes during meiosis to a lack of one chromosome in the offspring<br>Relates how fertilization can lead to a lack of one chromosome in the offspring	3
Links a problem during cell division to the absence of a chromosome	2
Provides some relevant information	1

Sample answer:

If homologous chromosomes in Meiosis I (or sister chromatids in Meiosis II) do not separate correctly, one gamete will end up with 2 copies of the same chromosome and another gamete will end up without a copy of this chromosome. After fertilisation, the gamete with no copy of sex chromosome has joined with a normal gamete to produce an individual with only one sex chromosome.

Supplied marking guidance · human reviewed

Compare this with your working, not only your final sentence.

Syllabus alignment

Module 5 · HeredityModule 6 · Genetic Change

Cell ReplicationModel mitosis, meiosis and DNA replication using nucleotide pairing and bonding.
MutationCompare causes, processes and effects of point and chromosomal mutations.
Genetic VariationPredict offspring variation by modelling meiosis, crossing over, fertilisation and mutation.

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