© Cengage Learning 2015

Biology Concepts and Applications | 9e

Starr | Evers | Starr

© Cengage Learning 2015

Chapter 13 Part 2

Observing Patterns in

Inherited Traits

Monohybrid Cross Practice #1

• A pea plant produces yellow peas and has the genotype of YY is crossed with a pea plant that produces green peas and has the genotype of yy.

– Draw a Punnett square of this cross. What are the predicted genotype and phenotype ratios of this cross?

• The F1 offspring of this cross are then crossed to each other.

– Draw a Punnett square of this cross. What are the predicted genotype and phenotype ratios of this cross?

Mendel’s Next Question: • What happens to the inheritance of two

different traits in the same cross?

Figure 9.4

Dominant Recessive

White

Pod shape Inflated Constricted

Flower position

Pod Color

Dominant Recessive

Flower color Purple

Axial Terminal

Green Yellow

Tall Dwarf

Seed shape Round Wrinkled

Seed color Yellow Green Stem length

Dihybrid

Crosses &

Independent

Assortment

Figure 13-8 p211

meiosis II

meiosis I

gamete genotype:

meiosis II

meiosis I

or

Pt pT PT pt

Independent

Assortment

Figure 13-10a p212

Other types of inheritance patterns: Incomplete Dominance in Snapdragons

Red x White = Pink

Codominance

• Both alleles are dominant in the heterozygote

• Blood typing as an example

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Pleiotropy – A single gene affects multiple traits

Example: Sickle cell disease

Individual homozygous

for sickle-cell allele

Sickle-cell (abnormal) hemoglobin

Abnormal hemoglobin crystallizes into long, flexible chains,

causing red blood cells to become sickle-shaped.

Sickled cells can lead to a cascade of symptoms, such as

weakness, pain, organ damage, and paralysis.

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Epistasis (Polygenic Inheritance) More than one gene acts on a single trait

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Does the environment affect phenotype?

“Nature vs. Nurture”