SBI3U – Assigned Work – Answer Sheet

Thursday, March 10, 2011

Learning Objective:To understand how heritable traits are passed on from one generation to another.

Success Indicators:To be able to explain using common genetic practices (e.g., Punnett Square) how genetic traits are passed on from one generation to the next, the probable numbers of each trait that would be observable in each generation and how to test for homozygous vs heterozygous genotypes.

Read Section 6.2:Genetic Analysis (pages 160 – 167)

Key terms:Punnett Square

Sutton-Boveri Hypothesis

Chromosome theory of heredity

Monohybrid vs Dihybrid crosses

Test Cross

Define:Punnett SquareWhat is a Punnett Square used for?

The following diagram is the basic Monohybrid Punnett Square:

Using the Punnett Square below, what offspring would be expected and their ratios (and percentages) from the following cross:

A Heterozygous Smooth Seed Shape Plant with a Heterozygous Smooth Seed Shape Plant

Describe the Chromosomal Basis of Heredity

Using the Punnett Square below, what offspring would be expected and their ratios (and percentages) from the following cross:

Homozygous Smooth Seed Shape, Heterozygous Tall Plant

Genotype: SSTt

Gametes: ST ST St St

with

Heterozygous Smooth Seed Shape, Homozygous Short Plant

Genotype: Sstt

Gametes: St St st st

Where:

Smooth Seed Shape ( S ) is dominant to Wrinkled ( s );Tall ( T ) plants are dominant to Short ( t )

Phenotypes from above cross:

Homozygous Smooth Seed Shape, Heterozygous Tall Plant / Homozygous Smooth Seed Shape, Heterozygous Tall Plant / Homozygous Smooth Seed Shape, Homozygous Short Plant / Homozygous Smooth Seed Shape, Homozygous Short Plant
Homozygous Smooth Seed Shape, Heterozygous Tall Plant / Homozygous Smooth Seed Shape, Heterozygous Tall Plant / Homozygous Smooth Seed Shape, Homozygous Short Plant / Homozygous Smooth Seed Shape, Homozygous Short Plant
Heterozygous Smooth Seed Shape, Heterozygous Tall Plant / Heterozygous Smooth Seed Shape, Heterozygous Tall Plant / Heterozygous Smooth Seed Shape, Homozygous Short Plant / Heterozygous Smooth Seed Shape, Homozygous Short Plant
Heterozygous Smooth Seed Shape, Heterozygous Tall Plant / Heterozygous Smooth Seed Shape, Heterozygous Tall Plant / Heterozygous Smooth Seed Shape, Homozygous Short Plant / Heterozygous Smooth Seed Shape, Homozygous Short Plant

Ratios of Genotypes from above cross:

1: SSTt; 1: SStt; 1: SsTt; 1: Sstt

What is a Test Cross?Why is a Test Cross performed?

Answer Page 160:

Understanding Concepts:2, 3

Applying Inquiry/Communication Skills:6 a & b, 7 a - c, 8 a - d, 9 a – c, 10