The maternal-effect mutation bicoid (bcd) is recessive. In the absence of the bicoid protein product, embryogenesis is not completed. Consider a cross between a female heterozygous for the bicoid alleles (bcd+ /bcd—) and a male homozygous for the mutation (bcd—/bcd—).

a. How is it possible for a male homozygous for the mutation to exist?
b. Predict the outcome (normal vs. failed embryogenesis) in the F1 and F2 generations of the cross described.

Explanation:

1.   bcd⁻/bcd⁻ ×   bcd⁺/bcd⁻

                         ↓

bcd⁺/bcd⁻,  bcd⁺/bcd⁻,  bcd⁻/bcd⁻,  bcd⁻/bcd⁻

∴ Male homozygous is possible.

2. Normal embryogenesis = bcd⁺/bcd⁺

Failed embryogenesis = bcd⁻/ bcd⁻

bcd⁺/bcd⁺  ×  bcd⁻/ bcd⁻

                  ↓

All progeny will be bcd⁺/bcd⁻ in the F1 generation.

∴ All of them will undergo normal embryogenesis.

3. In F2 generation,

bcd⁺/bcd⁻ × bcd⁺/bcd⁻

                  ↓

bcd⁺/bcd⁺ , bcd⁺/bcd⁻, bcd⁺/bcd⁻, bcd⁻/ bcd⁻

∴ 25% of them is normal and will undergo normal embryogenesis, 50% of them will undergo normal embryogenesis as bcd protein is present and 25% of them will not undergo embryogenesis as bcd protein is absent.

∴ 75% will undergo normal embryogenesis and 25% will not undergo embryogenesis.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.