Lesson 8 of 10

The big picture

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Here is the whole track in one table.

Heredity — the rules, lesson by lesson
Lesson	The rule
Resemble both, match neither	Each trait has two gene copies, one from each parent. One copy can hide the other. A child may match one parent in shape. It may match the other in colour.
The man who counted	Mendel used true-breeding lines, crossed them by hand, and counted every offspring. Counts turn a guess into a pattern you can test.
The hidden one comes back	A gene pair has two copies. A dominant copy shows in the plant. A recessive copy shows only when both copies are recessive.
The count is the argument	Two Tt plants are crossed. Each seed gets T or t from each parent. So the four pairs TT, Tt, Tt and tt are equally likely. Three of them give tall plants. One gives a short plant.
Two traits at once	Two gene pairs are passed on separately. That gives sixteen equally likely boxes. In big counts, the looks come near nine, three, three and one.
Which contribution decides	A parent with a mixed pair can pass either kind. A parent with a matching pair always passes the same kind. In people, the father has the mixed pair, XY. So the father's sperm decides the sex.
The laws in plain words	Dominance: one form of a gene can hide another. Segregation: a pair separates, and each parent passes one gene. Independent assortment: two gene pairs sort into gametes independently.

Now open your Class 10 Science book at Chapter 8, Heredity. You have counted its ratios yourself.