Biologymrsneal.com/numo/extensions/wysiwyg/uploads/u.2.Chapter... · 2016-01-28 · A Summary of Mendel's Principles A Summary of Mendel's Principles •Genes are passed from parents

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Copyright Pearson Prentice Hall

Biology

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11-3 Exploring Mendelian Genetics11–3 Exploring Mendelian

Genetics

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11–3 Exploring Mendelian Genetics

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Independent Assortment

What is the principle of independent

assortment?

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To determine if the segregation of one pair of

alleles affects the segregation of another pair of

alleles, Mendel performed a two-factor cross.


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The Two-Factor Cross: F1

Mendel crossed true-breeding plants that

produced round yellow peas (genotype RRYY)

with true-breeding plants that produced wrinkled

green peas (genotype rryy).

All of the F1 offspring produced round yellow

peas (RrYy).

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The alleles for round (R) and yellow (Y) are

dominant over the alleles for wrinkled (r) and

green (y).

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The Two-Factor Cross: F2

Mendel crossed the heterozygous F1 plants (RrYy)

with each other to determine if the alleles would

segregate from each other in the F2 generation.

RrYy × RrYy

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The Punnett square predicts a 9 : 3 : 3 :1 ratio in the

F2 generation.

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In Mendel’s experiment, the F2 generation produced the following:

• some seeds that were round and yellow

• some seeds that were wrinkled and green

• some seeds that were round and green

• some seeds that were wrinkled and yellow


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The alleles for seed shape segregated independently

of those for seed color. This principle is known as

independent assortment.

Genes that segregate independently do not influence

each other's inheritance.


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Mendel's experimental results were very close to the

9 : 3 : 3 : 1 ratio predicted by the Punnett square.

Mendel had discovered the principle of independent

assortment.


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The principle of independent assortment

states that genes for different traits can

segregate independently during the

formation of gametes.

Independent assortment helps account for

the many genetic variations observed in

plants, animals, and other organisms.


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A Summary of Mendel's

Principles

A Summary of Mendel's Principles

• Genes are passed from parents to their

offspring.

• If two or more forms (alleles) of the gene for a

single trait exist, some forms of the gene may

be dominant and others may be recessive.

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• In most sexually reproducing organisms, each

adult has two copies of each gene. These genes

are segregated from each other when gametes

are formed.

• The alleles for different genes usually segregate

independently of one another.

A Summary of Mendel's

Principles

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Beyond Dominant and

Recessive Alleles

What inheritance patterns exist aside from

simple dominance?

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Beyond Dominant and

Recessive Alleles

Some alleles are neither dominant nor

recessive, and many traits are controlled

by multiple alleles or multiple genes.

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Beyond Dominant and

Recessive Alleles

Incomplete Dominance

When one allele is not completely dominant over

another it is called incomplete dominance.

In incomplete dominance, the heterozygous

phenotype is between the two homozygous

phenotypes.

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A cross between

red (RR) and

white (WW) four

o’clock plants

produces pink-

colored flowers

(RW).

Beyond Dominant and

Recessive Alleles

WW

RR

Resources/ActiveArt/punnetSquares.html


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Beyond Dominant and

Recessive Alleles

Codominance

In codominance, both alleles contribute to the phenotype.

In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers.

Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.

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Beyond Dominant and

Recessive Alleles

Multiple Alleles

Genes that are controlled by more than two alleles

are said to have multiple alleles.

An individual can’t have more than two alleles.

However, more than two possible alleles can exist

in a population.

A rabbit's coat color is determined by a single gene

that has at least four different alleles.

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Beyond Dominant and

Recessive Alleles

Different combinations of alleles result in the colors

shown here.

Full color: CC, Ccch, Cch, or CcChinchilla: cchch, cchcch, or cchcHimalayan: chc, or chchAIbino: cc

KEY

C = full color; dominant

to all other alleles

cch = chinchilla; partial

defect in pigmentation;

dominant to

ch and c alleles

ch = Himalayan; color in

certain parts of the

body; dominant to

c allele

c = albino; no color;

recessive to all other

alleles

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Beyond Dominant and

Recessive Alleles

Polygenic Traits

Traits controlled by two or more genes are said to

be polygenic traits.

Skin color in humans is a polygenic trait controlled

by more than four different genes.

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Applying Mendel's

Principles

Applying Mendel's Principles

Thomas Hunt Morgan used fruit flies to advance

the study of genetics.

Morgan and others tested Mendel’s principles and

learned that they applied to other organisms as

well as plants.

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Applying Mendel's

Principles

Mendel’s principles can be used to study inheritance

of human traits and to calculate the probability of

certain traits appearing in the next generation.

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Genetics and the

Environment

Genetics and the Environment

Characteristics of any organism are determined by

the interaction between genes and the

environment.

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- or -

Continue to: Click to Launch:

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11–3



Resources/ch11_sectn03_quiz.qtb




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11–3

In a cross involving two pea plant traits,

observation of a 9 : 3 : 3 : 1 ratio in the F2

generation is evidence for

a. the two traits being inherited together.

b. an outcome that depends on the sex of the

parent plants.

c. the two traits being inherited independently

of each other.

d. multiple genes being responsible for each

trait.

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11–3

Traits controlled by two or more genes are called

a. multiple-allele traits.

b. polygenic traits.

c. codominant traits.

d. hybrid traits.

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11–3

In four o'clock flowers, the alleles for red flowers

and white flowers show incomplete dominance.

Heterozygous four o'clock plants have

a. pink flowers.

b. white flowers.

c. half white flowers and half red flowers.

d. red flowers.

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11–3

A white male horse and a tan female horse

produce an offspring that has large areas of

white coat and large areas of tan coat. This is

an example of

a. incomplete dominance.

b. multiple alleles.

c. codominance.

d. a polygenic trait.

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11–3

Mendel's principles apply to

a. pea plants only.

b. fruit flies only.

c. all organisms.

d. only plants and animals.

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Biologymrsneal.com/numo/extensions/wysiwyg/uploads/u.2.Chapter... · 2016-01-28 · A Summary of Mendel's Principles A Summary of Mendel's Principles •Genes are passed from parents