Bio 12.1 and 12.2 LESSON

The Work of Gregor Mendel

Learning Objectives

▪ Explain from where an organism gets its unique

characteristics.

▪ Explain how different forms of a gene are distributed to

offspring.

▪ Explain how probability can be used to predict inherited

traits.

▪ Explain how alleles segregate when more than one gene

is involved.

▪ Identify Mendel’s contributions to our understanding of

genetics.

Mendel’s Experiments

•Peas are a “model system.”

•Started with “true breeding” plants

•Trait: specific characteristic (e.g., seed color, plant height) of an
individual

•Hybrid: created from cross of true-breeding individuals

Multiple Choice

Traits are

• characteristics

• genes

• DNA

• offspring

Multiple Select

Why are pea plants a good model for studying genetics?

• They reproduce quickly

• They produce lots of offspring

• They produce few offspring

• They take a long time to reproduce

Pollination in Pea Plants Cross Pollination

Pea Characteristics

Genes and Alleles

• Genes: passed from one generation to the next; determine an individual's characteristics.

• Alleles: the different forms of a gene

Characteristics such as seed color
are determined by .

Yellow and green seed colors are
determined by .

The allele for round seeds is
to the allele for wrinkled.

genes

alleles

dominant

Drag and Drop

Characteristics such as seed color are determined by ​

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Yellow and green seed colors are determined by ​

Placeholder

The allele for round seeds is ​

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to the allele for wrinkled.

Drag these tiles and drop them in the correct blank above

genes

alleles

dominant

recessive

Principle of Dominance

• Some alleles are dominant, some recessive.

• An organism with at least one dominant allele will exhibit that trait.

• An organism with a recessive allele will exhibit the trait only in

the absence of a dominant allele.

Mendel’s F1 Crosses

When Mendel crossed plants with contrasting traits, the hybrid
offspring showed traits of only one parent.

Multiple Choice

When Mendel crossed plants with contrasting traits, the hybrid offspring showed

• traits of both parents

• traits of one parent

• traits different from both parents

• no traits

Segregation

Segregation: separation of alleles during gamete formation

Mendel was interested in
why some traits seemed
to “disappear”.

Notice the color yellow
disappeared for a
generation.

Multiple Choice

What did Mendel find so interesting about these crosses?

• The yellow trait seemed to disappear for a generation.

• The green trait showed up in every generation.

• The green and yellow colors never mixed.

• The yellow peas tasted weird.

The F1 Generation

P parent

F1 offspring

Multiple Choice

What percentage of the parent generation was green?

• 0

• 50

• 100

• no way to tell

Multiple Choice

What percentage of the offspring was green?

• 0

• 50

• 100

• no way to tell

The F2 Generation

What proportion of F2
offspring were yellow?

What proportion of F2
offspring were green?

1/4

3/4

Multiple Choice

What percentage of the F2 generation is green?

• 0

• 25

• 50

• 75

• 100

The Formation of Gametes

Multiple Choice

What is it called when alleles separate into gametes?

• segregation

• integration

• fertilization

• inheritance

Probability and Heredity

Probability: the likelihood an event will occur. If
you flip a coin, what is the

•probability of either outcome:

• Three coin tosses?

• Each flip is an independent event.

50% or 1/2

1/2 × 1/2 × 1/2 = 1/8

Multiple Choice

What is the likelihood that an event will occur?

• probability

• segregation

• independence

• dependence

Using Segregation to Predict Outcomes

Probability of a gamete receiving a G?

Probability of gamete receiving a g?

Probability of green offspring is
.

Probability of yellow offspring is
.

50%, or 1/2

50%, or 1/2

3/4

1/4

Multiple Choice

What is the probability of a green offspring in this cross?

• 0/4

  (0)

• 1/4

• 2/4

  (1/2)

• 3/4

• 4/4

  (1)

Genotype and Phenotype

Two organisms may share the same
but have different genotypes .

phenotype

Genotype: genetic makeup

Phenotype: physical traits

Categorize

Options (7)

genetic makeup

GG

gg

Gg

physical trait

yellow

green

Organize these options into the right categories

genotype

phenotype

Heterozygous and Homozygous

Homozygous: has two identical alleles for a gene

Heterozygous: has two different alleles for a gene

Which are:
homozygous? heterozygous?

1

2

3

1, 4

2, 3

4

Drag and Drop

​

Placeholder

means there are two different alleles for a gene.

​

Placeholder

means there are two identical alleles for a gene.

Drag these tiles and drop them in the correct blank above

Heterozygous

Homozygous

Making a Punnett Square

Combine gamete genotypes

Gametes for a parent

along one side

Possible gametes

A cross of ospreys:

beak size (B, b)

Multiple Choice

What belongs in the last box?

• RR

• Rr

• rr

• ff

Multiple Choice

Look at the punnett square shown. What allele pair would replace the "?"

• WW

• Ww

• ww

Multiple Choice

Look at the punnett square. What is the probability that the offspring would have homozygous alleles for the trait?

• 100%

• 75%

• 50%

• 25%

• 0%

Making a Punnett Square: Two Factors

Combine gamete genotypes

A cross of pea plants:

size (T, t) and pod color (G, g)

All possible gametes

All gametes for a parent

along one side

The Two-Factor Cross: F1

The Two-Factor Cross: F2
Independent assortment: Genes for different traits can segregate independently during gamete formation.

Multiple Choice

What does it mean that genes can segregate INDEPENDENTLY of each other?

• one of them affects the other

• they have no effect on each other

• each is affected by the other

• the alleles separate into gametes

Summary of Mendel’s Principles, Part I

Inheritance is determined by units called , which are
passed from parents to offspring.

Where more than one form of a gene for a single trait exists,
some alleles may be and others .

genes

dominant

recessive

Multiple Choice

Inheritance is determined by units called ​ _____, which are passed from parents to offspring.

• genes
• phenotypes

• fertilization

• cross-pollination

Multiple Select

When more than one form of a gene for a single trait exists, alleles can be _____.

(Choose TWO)

• dominant

• recessive

• fertilized

• pollinated

Summary Mendel’s Principles, Part II

• Each adult has two copies of each gene—one from each
parent. These genes from each other when
gametes are formed.

• Alleles for different genes usually segregate
of each other.

segregate

independently

Drag and Drop

Each adult has two copies of each gene—one from each parent. These genes ​

Placeholder

from each other when gametes are formed.

Alleles for different genes usually segregate ​

Placeholder

of each other.

Drag these tiles and drop them in the correct blank above

segregate

independently

dependently

mutate