In the wasp Bracon hebetor, a form of parthenogenesis (the development of unfertilized eggs into progeny) resulting in haploid organisms is not uncommon. All haploids are males. When offspring arise from fertilization, females almost invariably result. P. W. Whiting has shown that an X-linked gene with nine multiple alleles (Xₐ, Xb, etc.) controls sex determination. Any homozygous or hemizygous condition results in males, and any heterozygous condition results in females. If an Xₐ/Xb female mates with an Xₐ male and lays 50 percent fertilized and 50 percent unfertilized eggs, what proportion of male and female offspring will result?

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Hi everyone. Let's take a look at this practice problem Together we have supposed that in an insect unfertilized eggs develop into males via parthenogenesis. On the contrary fertilized eggs in the homosexuals condition result in males. Whereas fertilized AIDS in the hetero ziggy's condition Result in females assume that an ex wife female mates with an ex male and produces 60% unfertilized eggs and 40% fertilized eggs identify the ratio of male to female offspring in such a case. Okay we just took in a whole bunch of information so let's remind ourselves what it is exactly. The practice problem is asking we need to identify the ratio of male to female offspring when an Xy male excuse me ex wife female mates with an ex male. And we can see that all of our answer choices are a ratio And we are told that Of eggs are unfertilized and 40% are fertilized when a female mates with a male. So in this instance we have 60% are unfertilized And 40% are fertilized. Now from the very beginning of the problem we were told that unfertilized eggs develop into males. So we know that this 60% of unfertilized eggs are automatically male. And we are also told that fertilized eggs can either be homo or hetero sickness and that determines whether they're male or female. And so in this fertilized eggs you get 50% R. X. X. And 50% are Xy. When the offspring are fertilized and headers. I guess you get female star xy will be female and our homes. I guess fertilized eggs will be male. But recall that this 50% is of the 40% total eggs. So that means actually that this is 20% male of the total eggs because 50% of 40 is 20 and 50% of 40 is also 20. So 20% of the fertilized eggs are male and 20% of the fertilized eggs are female. Now we need to add up our totals of unfertilized plus fertilized eggs. So our males Will have 60% unfertilized plus 20% fertilized and are female Is just 20% fertilized eggs. So that gives us an 80% over Which is a 4-1 ratio. And if we take a look at our answer choices. D. is our correct answer. 4-1. Alright everyone. I hope that by breaking this down, reminding ourselves what it is we're trying to answer and then looking at the practice problem for clues and working out a key that going through this step by step made a little bit more feasible. It was a lot of information but we got through it together. I hope you found this helpful and I'll see you soon for the next practice problem

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Key Concepts

Parthenogenesis

Sex Determination and X-linked Genes

Genetic Cross and Offspring Ratios