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Course: Class 10 Biology (India)>Unit 4

Lesson 2: Heredity & Mendel's experiment

Dominance & segregation laws

Let's learn Mendel's law of dominance & segregation. Created by Mahesh Shenoy.

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• Are the dominant traits for one org. always dominant for the entire species ?
Consider there are two pairs of rabbits, each pair has one black(pure) and one white(pure) , they each have 1 offspring .
Is it possible for 1 offspring to be black and the other white?
• Good question, but you should have specified which trait is dominant and which one is recessive. For the sake of the answer, I'm taking black coat as the dominant trait and white as recessive.

Let's denote black-coat rabbit as BB. Then, white-coated rabbit becomes bb. When crossing BB and bb, gametes form (B, B, b, b) according to the law of segregation. The gametes of the BB rabbit fertilize the gametes of bb rabbit and the offspring would be Bb.

According to the law of dominance, since black coat is the dominant trait and the offspring has a dominant allele (or the dominant version of the trait), the offspring would be black-coated.

So, to answer your question, no. Since we observe black is the dominant trait, the offspring of the pure rabbits will be the same. BUT, if you take the offspring (Bb) and cross them (in your Q you had two pairs, so two offsprings), there will be four different gamete combinations (BB, Bb, Bb, bb). Check the link out for more clarity: https://cdn.kastatic.org/ka-perseus-images/8a2d0abbcd2659115496a7f3254270a52cc02fc7.png

Here, three of the combinations have a dominant allele, hence a 75% chance for their offspring to be black. But, one of the combinations was "bb", meaning it has only recessive traits, i.e., there's a 25% chance for the offspring to be white.

Sorry for the long answer, and I hope it doesn't confuse you more. :)
• onwards what does he mean "some sperms get T and some t"?
what does it mean, specifically?
shouldn't it be half or something?