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Genetics — Part 1: Terms, Mendel and the monohybrid cross

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Lesson

Genetics

Part 1 — the language of genetics, Mendel’s experiments and the monohybrid cross.

In this lesson you will

Define the terms gene, allele, dominant, recessive, homozygous, heterozygous, phenotype, genotype, mutation and variation
State Mendel’s three laws and explain why he chose the garden pea
Work out a monohybrid cross to the F2 and derive the 3 : 1 and 1 : 2 : 1 ratios

Concept

Key terms

Table of eight genetic terms with meanings and pea examples
Term	Meaning	Pea example
Gene	Unit of heredity on a chromosome	Gene for flower colour
Allele	One of the alternative forms of a gene	V (violet) and v (white)
Dominant	Shows its effect even in a single copy	V
Recessive	Shows only when two copies are present	v
Homozygous	Two identical alleles	VV or vv
Heterozygous	Two different alleles	Vv
Genotype	Genetic make-up	Vv
Phenotype	Visible character	Violet flowers

Concept

Mutation and variation

Table defining variation and mutation
Term	Meaning
Variation	Differences among individuals of the same species
Mutation	A sudden heritable change in a gene or chromosome; a source of new variation