Page 197 - Science Course 3 (Book 1)

Genetic Outcomes Mo5-L2a: What is Punnett Square?
Lesson 2

Let’s Begin

In this topic, you will learn the following
lessons: Rediscovering Mendel’s Work
In 1900, scientists realized that
Mo.5–L2a: What is Punnett Square? genes were on chromosomes in the nucleus.
Mo.5–L2b: What are the Patterns of Inheritance?
Mo.5–L2c: Why are Diseases Inherited?

Mo5-L2a What is Punnett Square? They confirmed that genes were Mendel’s dominant
and recessive factors.
KEY CONCEPTS:
1. How can you use models to predict genetic out- Predicting Genetic Outcomes
comes?
If you flipped a coin ten times, you might predict a
heads-to-tails ratio of 5:5.
Vocabulary A-Z Probabilities are predictions;
they do not guarantee
Let us learn some vocabulary outcomes. Your coin flips
could result in ten heads in
Monohyrid Cross a row.
a cross between two individuals that are hybrids for
one trait.
Mendel predicted the outcome of a monohybrid
parent’s phenotype tall tall cross—a cross between two individuals that are
hybrids for one trait.
parent’s phenotype Hh Hh
Mendel predicted a 3:1 ratio of the dominant
phenotype to the recessive phenotype.

gamete’s
phenotype H h H h

zygote’s
phenotype HH Hh Hh hh
Purple (PP) White (Pp)
zygote’s
phenotype tall tall tall short

Punnett Square
a model that
is used to show y y Purple (Pp)
the probability
of all possible
genotypes
and phenotypes Y
of offspring.
Yy Yy

y PP Pp Pp pp

yy yy 3 Purple : 1 White

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