The Story of the Twins Who Weren't

Bio4241 - Final exam questions, 2015

BONUS QUESTION

The Story of the Twins Who Weren't

In a 1970s science fiction novel, the genetics thought problem illustrated above is presented as a possibility given advanced biotechnology. Starting with a single Primary Oocyte from one parent and a single Primary Spermatocyte from another unrelated parent, both products of a single First Meiosis are recovered, so that the two Secondary Oocytes and Spermatocytes cells contain complementary sets of chromosomes from the two parents. Second Meiosis produces a mature egg or sperm from each cell; note that one sperm bears an X and the other a Y chromosome. One Egg is fertilized withthe Y Sperm, and the other Egg' with the X Sperm'. The zygotes are raised to maturity.

Questions

1. Are the two persons 'related'? In what sense? Are they cousins? Are they brother and sister? Are they twins? Explain

2. Would you expect them to look alike? Explain.

3. What fraction of their microsatellite fingerprint alleles would they be expected to share? Explain.

4. Suppose the two persons wish to marry and have children [in the novel, this is the central question]. Is a child born to this couple substantially more or less likely to have an autosomal recessive genetic disease, than a more typical couple? Explain your reasoning.

[For further thought (not part of the bonus question): what about autosomal dominant, X-linked dominant and recessive, Y-linked, and mtDNA-linked genetic diseases? How would meiotic crossing-over affect the answer?