Genetics & Heredity

Using the vocabulary to discuss and predict the outcome of

genetic crosses

Objectives

• By the end of this interactive presentation you– Will have reviewed key genetics vocabulary

already discussed in class– Will be able to distinguish between genotype

and phenotype– Will be able to analyze data from a genetics

experiment in order to predict your genotype for various traits.

Why do we call Mendel the “Father of Genetics?”

A. He was the first person to discover genes.

B. He understood that DNA was where genes were.

C. He was the first person to see chromosomes.

D. His was the first person to study inheritance in depth.

Reviewing Mendel

Mendel observed that some traits seemed to “mask” or override other traits.

What did Mendel call these traits?

A. Dominant traits

B. Recessive traits

C. Co-dominant traits

Reviewing Mendel

• Mendel called the traits that seemed to “overpower” others dominant traits.

• We represent the allele for dominant traits with a capital letter.

• For example, – Tall is dominant over short, T– Round is dominant over wrinkled, R– Yellow is dominant over green, Y

Reviewing Mendel

• The traits that were masked were called recessive traits.

• We represent the allele for a recessive trait with a lowercase letter.

• For example– Short (recessive to tall), t– Wrinkled (recessive to round), r– Green (recessive to yellow), y

Reviewing Mendel

Which individual will express the recessive short trait?

A. Tt

B. TT

C. tt

Punnett Squares

• On a piece of loose leaf create and complete a Punnett Square to predict the outcome of the following genetic cross

• Round peas are dominant to wrinkled. What are the possible outcomes if a RR plant was crossed with a Rr plant?

Punnett SquaresRR x Rr

RR Rr

RR Rr

R

R

R r

Punnett Squares

In the previous Punnett Square, what are the odds of having a heterozygous

offspring?

A. 100%

B. 75%

C. 50%

D. 25%

Vocabulary Review

• Remember:

• Homozygous means 2 of the same allele.– Homophone: words that sound the same.

• Heterozygous means 2 different alleles.– Heterogeneous: a mixture that is different

throughout. (For example, when your iced tea is sweet at the bottom, but not at the top)

New Vocabulary

• Phenotype – The physical characteristic (trait) that is expressed is

the phenotype.

• Genotype– The alleles or the genes that the organism has.

• For example:– Tt is the genotype, tall is the phenotype– RR is the genotype, round is the phenotype– yy is the genotype, green is the phenotype

Let’s Practice

• What is the phenotype of…– Yy– SS– pp– YY– ss

Trait Dominant Gene

Recessive Gene

Seed

Color

Yellow

(Y)

Green

(y)

Pod

Shape

Smooth

(S)

Pinched

(s)

Flower

Color

Purple

(P)

White

(p)

Let’s Practice

• Determine the genotypes– Green seeds– Pinched pods– White flowers

Trait Dominant Gene

Recessive Gene

Seed

Color

Yellow

(Y)

Green

(y)

Pod

Shape

Smooth

(S)

Pinched

(s)

Flower

Color

Purple

(P)

White

(p)

Let’s Practice

We can only predict the genotype of Individuals expressing dominant traits.

Why might this statement be true?

A. Dominant traits are less common.

B. A dominant phenotype must mean 2 dominant alleles.

C. A dominant phenotype could mean 2 dominant alleles OR 1 dominant and 1 recessive allele.

For example

• Yellow seeds are dominant to green seeds. A pea plant producing yellow seeds can be either YY or Yy.– Without knowing more information about the

parents, you cannot be positive.

• On the other hand, a pea plant producing green seeds MUST be yy.– In order for the recessive allele to show, you

must have 2 recessive alleles.

Let’s Practice

• For each phenotype, give the genotype(s) that are possible.– Yellow– Smooth– Purple

Trait Dominant Gene

Recessive Gene

Seed

Color

Yellow

(Y)

Green

(y)

Pod

Shape

Smooth

(S)

Pinched

(s)

Flower

Color

Purple

(P)

White

(p)

Time to Review!

The factors that control our traits are called…

A. Alleles

B. Traits

C. Genes

D. Chromosomes

Time to Review!

An organism who is homozygous has

A. Two different alleles

B. Two dominant alleles

C. Two recessive alleles

D. Two of the same alleles, recessive or dominant.

Time to Review!

The different forms of a gene are called

A. Traits

B. Genotype

C. Genes

D. Alleles

Time to Review!

Which of the following is a genotype?

A. Yellow

B. Homozygous

C. Rr

Time to Review!

Which of the following is a phenotype?

A. Yellow

B. Homozygous

C. Rr

The End