The F1 generation of a cross between a red cock and white hen were all red because the gene for the

Analyze the question: A red cock is crossed with a white hen. All the F1 offspring are red. We need to explain why.

Concept: In Mendelian genetics, when two pure-breeding parents with contrasting traits are crossed, the F1 generation shows only one of the traits. The trait that shows up in the F1 is called the dominant trait. The trait that is hidden is the recessive trait. The hidden trait is not lost. It reappears in the F2 generation.

Solution:

Let R = gene for red (dominant) and r = gene for white (recessive).

• Parents: RR (red cock) × rr (white hen)
• Gametes: R and r
• F1: all Rr, which are all red

Because every F1 bird has both genes (Rr) but looks red, the red gene is masking the white gene. This means the red colour is dominant over white.

Checking the options:

• A. Wrong. The white gene did segregate during gamete formation. It is just masked in the F1.
• B. Correct. Red is dominant, so it is expressed in the heterozygous F1.
• C. Wrong. If white were dominant, the F1 would be white.
• D. Wrong. If red were recessive, the F1 would show white, not red.

Answer: B

Tip: In a monohybrid cross, the colour or trait that appears in all the F1 is the dominant one. If you see "all F1 showed trait X," think "X is dominant." Then, in F2, expect a 3:1 ratio of dominant to recessive.