Unit 7
Inheritance.
How traits pass to offspring: dominant and recessive alleles, the Punnett square, chance, and genes on the X chromosome.
Before this unit
- Cell division
- Probability Mathematics
The unit, lesson by lesson
Lessons
4 lessons · 20 practice questions · about 2 hours
Genes and alleles
Two copies of every gene, a dominant allele hiding a recessive one, genotype and phenotype, and why a white flower can come from two purple parents.
Punnett squares
How to build a Punnett square from what each parent can pass on, the 1 : 2 : 1 ratio of genotypes and 3 : 1 of colours, and a test cross that reveals a hidden genotype.
Chance and offspring
The Punnett square as a map of chances: an expected number of offspring, Mendel's counts, why a small sample strays from the ratio, and multiplying the chances of different offspring.
Sex-linked traits
Genes on the X chromosome: why colour blindness is common in men, how a carrier mother passes it to half her sons, and why the daughters of the same parents are carriers, not colour-blind.