Wrap-Up Questions

1. Explain why autosomal aneuploidies result in far more severe phenotypic consequences than sex chromosome aneuploidies.

2. Haploinsufficient genes are rare on the X-chromosome of humans and other mammals.  But there are many haploinsufficient genes on the Drosophila X-chromosome[1]. Explain why, given the differences in dosage compensation in each species.  (Hint: remember that haploinsufficient genes require the action of both copies of the gene to produce the phenotypic effect.)

3. In birds, males are the homogametic sex and females are the heterogametic sex. Draw a modified Punnett Square that tracks the inheritance of a Z-linked recessive trait from the cross ZaW x ZAZA.

Science and Society

4. The term Differences of Sex Development (DSD) is used to describe conditions in which a person’s sex phenotype is different from what is most common for their genotype.  This reflects a recent transition in vocabulary: in the past, DSDs were more frequently described as Disorders of Sex Development. In your opinion, what does the change in terminology indicate about changing views of society?

  1. de Clare, M., Pir, P. & Oliver, S. G. Haploinsufficiency and the sex chromosomes from yeasts to humans. BMC Biology 9, 15 (2011).


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