Page 139 - Science Course 3 (Book 1)

Genetic Inheritance Mo4-L2a: What Controls Traits?
Lesson 2

phenotype
how a trait appears or is expressed.
In this topic, you will learn the following
lessons:
genotype

Mo.4–L2a: What Controls Traits? the alleles of all the genes on an organism’s
Mo.4–L2b: What are the Patterns of Inheritance? chromosomes; controls an organism’s phenotype.

Mo4-L2a What Controls Traits? PHENOTYPE GENOTYPE

KEY CONCEPTS:
PP
1. What determines the expression of traits? Purple (homozygous)

Pp
Vocabulary A-Z Purple (heterozygous)
Let us learn some vocabulary

Purple Pp
gene (heterozygous)
a section of DNA on a chromosome that has genetic
information for one trait. pp
White (homozygous)

Homozygous
a genotype in which the alleles of a gene are
the same.

Heterozygous
a genotype in which the alleles of a gene
are different

allele
a different form of a gene.
Let’s Begin
allele

What Controls Traits

Mendel concluded that two factors—one from each
parent —control each trait.

Mendel’s “factors” are part of chromosomes which
exist as pairs—one chromosome from each parent.

Each cell in an offspring organism contains
chromosomes from both parents.

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