Q1.
How many combinations of characters can gametes carry?
Answer
A very large number — because each chromosome pair separates independently of every other pair during meiosis. If there are n pairs, the number of different gametes is 2n.
number of gamete types = 2n, where n = number of chromosome pairs
n = 3 (Activity 11.4) → 23 = 8
n = 23 (human) → 223 = 8,388,608 ≈ 84 lakh kinds of gamete
zygotes possible = 223 × 223 = 246 = 70,368,744,177,664 ≈ 7.0 × 1013
n = 3 (Activity 11.4) → 23 = 8
n = 23 (human) → 223 = 8,388,608 ≈ 84 lakh kinds of gamete
zygotes possible = 223 × 223 = 246 = 70,368,744,177,664 ≈ 7.0 × 1013
Why the powers of 2 appear: take one pair at a time. A gamete gets either the chromosome that came from the mother or the one that came from the father — two choices. The next pair is decided quite separately, giving two more choices, and so on. Three independent two-way choices give 2 × 2 × 2 = 8 outcomes; twenty-three of them give 223. And since a zygote is formed by one gamete from each parent, the counts multiply again.
Tip: notice what this does not require. There is no need for anything unusual to happen — no damage, no accident. Ordinary meiosis, working normally, guarantees that no two of your gametes are likely to be the same. That is why variation is a built-in feature of sexual reproduction and not a rare event.