Question

In Holstein cattle, the allele for black hair colour (B) is dominant over the allele for red hair colour (b), and the allele for hornless (P), or hornless, is dominant over the allele to have horns. What is the expected phenotypic ratio of the offspring of a BbPp x bbpp cross if these alleles are classified independently?

A. 1:1 Black, hornless: Red, horned
B. 3:1 Black, hornless: Red, horned
C. 1:1 Black: Red
D. None of the above

Answer 1

The expected phenotypic ratio of the offspring from a BbPp x bbpp cross in Holstein cattle for hair color and presence of horns is 1:1, with 1 being Black, hornless and 1 being Red, horned. This is because the dominant alleles are B for black hair and P for hornlessness.

Step-by-step explanation:

To determine the expected phenotypic ratio of the offspring from a BbPp x bbpp cross in Holstein cattle, we need to understand how these alleles work. The allele for black hair colour (B) is dominant over the allele for red hair colour (b), and the allele for being hornless (P) is dominant over the allele to have horns (p). Because of independent assortment, each trait is inherited separately.

From a BbPp parent, an offspring can inherit either B or b for hair color and P or p for horn presence. From a bbpp parent, an offspring can only inherit b for hair color and p for the horns. When we cross these two, the possible combinations for the offspring are BbPp, Bbpp, bbPp, and bbpp.

The Bb and bb combinations determine black or red hair, respectively, since B is dominant. Similarly, Pp and pp determine whether the cattle will be hornless or horned, since P is dominant.

The resulting phenotypic ratio will be in terms of black or red, and hornless or horned. The offspring will be:

• Black, hornless: This results from either BbPp or Bbpp combinations.
• Red, horned: This results from bbPp or bbpp combinations.

Since there are two ways to be black and hornless (BbPp and Bbpp) and two ways to be red and horned (bbPp and bbpp), the expected phenotypic ratio is 1:1.