Question

Most women produce one egg per month. Use your knowledge of the menstrual cycle and oogenesis to explain how Dan’s mother produced an egg carrying the u allele.

She is heterozygous carrier Uu

Answer 1

The mother is heterozygous for the U gene. Her genotype is Uu. The mother produces gamete by the process of meiosis. The homologous chromosomes are separated during the anaphase 1 of meiosis. In this way, the U chromosome is separated to one pole and the another u chromosome is separated towards other pole. This leads to produce secondary oocyte and one polar body. The secondary oocyte has u chromosome whereas the first polar body has U chromosome.

Now when this secondary oocyte is activated by the sperm, then the second meiosis division in secondary oocyte is completed. This leads to produce u in the egg nucleus and in the secondary polar body. The secondary polar body is degenerated. The egg nucleus is fused with male gamete and produces Dan. That's why Dan has u allele in her genotype.