Page 191 - Science Course 3 (Book 1)

Mo5-L1b: What did Mendel Discover About Heredity?

Recessive Trait Homozygous
a genetic factor that is blocked by the presence of a a genotype in Homozygous
BB
dominant factor. which the two bb
alleles of a
gene are the
Carrier Carrier same.
Father Mother

R r R r

R R R r R r r r

Let’s Begin

Normal Carrier Carrier Affected
Heredity—the History and the Basics
Genotype
the alleles of all the genes on an organism’s Selective breeding is the selection and breeding of
organisms for desired traits.
chromosomes; controls an organism’s phenotype.
In the illustration below, a farmer would breed the
Phenotype rooster with the hen that produces the most eggs
how a trait appears or is expressed. per year.

Phenotype Genotype
PP 1
Purple
(homozygous)

3 Pp
Purple
(heterozygous)
2
Pp
Purple
(heterozygous)

pp 180 eggs 280 eggs 230 eggs
White
1 (homozygous) 1 per year per year per year
ratio 3:1 ratio 1 : 2 : 1

In 1856, Gregor Mendel began experimenting with

Heterozygous pea plants to answer the question of how traits are
inherited.
a genotype in Heterozygous
which the two Bb
alleles of a gene
are different.

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