Chapter 9Section 1 Review

1. .

1. Describe what a true-breeding plant is.

Plants that are true-breeding for a trait always produce offspring with that trait when they self-pollinate

purebreds

2. Outline how Mendel produced plants that had genes for both contrasting traits of a characteristic.

He first produced true-breeding plants. Then he crossed the true-breeds. He allowed the offspring (F1) to self-

pollinate and this produced contrasting traits in the F2 generation.

3. Define the terms dominate and recessive.

Dominant- the factor that controls the characteristic; masks or dominates the recessive.

5. Differentiate genes from alleles.

Gene- a segment of DNA on a chromosome

Allele- alternative form of a gene

6. How did Mendel’s F1 generation plants differ from his F2 generation plants?

F1- all offspring exhibited the dominant allele

F2-was a result of allowing F1 offspring to self-pollinate; a 3:1 ratio

7. Many inherited disorders of humans appear in children of parents who do not have the disorder. How can you explain this?

The disease is recessive and each parent is a carrier; heterozygous

8. During meiosis, what allows genes located on the same chromosome to separate independently of one another?

Crossing-over

Section 2: Genetic Crosses

Genotype- the alleles that the organism inherits from its parents (PP, Pp or pp)

Phenotype- an organism’s appearance

Homozygous- when both alleles of a pair are the same; BB or bb

(dominant or recessive)

Heterozygous- when both alleles are different; Bb

Probability

The likelihood that a specific event will occur

Probability= # of times an event is expected to happen # of times an event could happen

Mendel studied statistics in math

Monohybrid cross

A cross that looks at just one trait; shows 4 offspring

Dihybrid cross

Tracks two traits at the same time; 16 offspring

Test Cross

A cross performed between an unknown genotype and a homozygous recessive individual

Helps to determine to genotype of an individual whose phenotype expresses the dominant trait

Example…

½ would be expected to be brown if the genotype of your black guinea pig was Bb. None would be brown if the genotype was BB.

BB or Bb? (Black) B b

bb

Bb bb

Bb bb

Complete dominance

All of the traits Mendel studied exhibited complete dominance. Every phenotype was either dominant or recessive. There was no “in-between”

In complete dominance the heterozygous and homozygous dominant genotypes look the same.

(BB or Bb)

Example:

There were no medium sized plants in Mendel’s studies

Incomplete dominance

Most traits work like this… This is when the phenotype of the

heterzygote looks different than either parent

Codominance

Each alleles for a gene is expressed in heterozygous offspring; neither allele is dominant or recessive

Written with 2 caps; AB

Examples…