Lesson 1 of 11 · 6 min

Mendel's laws of inheritance

NCERT § "Mendel's Laws of Inheritance"

Long before anyone knew what a gene was, a monk spent seven years counting pea plants by hand — and found numbers so exact they still show up on NEET papers today.

The story this chapter follows: Three generations, one family

Meet a family across three generations: a grandfather who has grown pea plants as a hobby for decades, his children, and his grandchildren. Their own eye colour, blood groups and family history of colour blindness, together with the grandfather's pea patch, carry every idea in this chapter.

The lesson in notes

In short

Inheritance is the transfer of characters from parents to progeny and is what heredity rests on; variation is how far the progeny differ from their parents.

Gregor Mendel ran hybridisation experiments on garden pea for seven years, from 1856 to 1863, and proposed the laws of inheritance from them.

His pea work marked the first use of statistical analysis and mathematical logic on a problem in biology, and his large sample sizes made his data more credible.

He began with 14 true-breeding pea varieties that formed pairs differing in one character with two contrasting forms. A true-breeding line keeps showing the same trait after many generations of self-pollination.

The seven characters and their dominant form: stem height (tall), flower colour (violet), flower position (axial), pod shape (inflated), pod colour (green), seed shape (round), seed colour (yellow). The recessive forms are dwarf, white, terminal, constricted, yellow pod, wrinkled seed and green seed.