biology - loudoun county public schools...punnett squares punnett square the gene combinations that...

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Copyright Pearson Prentice Hall

biology

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11-1 The Work of Gregor Mendel


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Gregor Mendel’s Peas

Genetics is the scientific study of heredity.

Gregor Mendel was an Austrian monk. His work

was important to the understanding of heredity.

Mendel carried out his work with ordinary garden

peas.


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Mendel knew that

• the male part of each flower produces pollen, (containing sperm).

• the female part of the flower produces egg cells.

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During sexual reproduction, sperm and egg cells join

in a process called fertilization.

Fertilization produces a new cell.

Pea flowers are self-pollinating.

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Mendel had true-breeding pea plants that, if allowed

to self-pollinate, would produce offspring identical to

themselves.

Cross-pollination

Mendel was able to

produce seeds that

had two different

parents.

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Notes

• What is Genetics?

Study of inheritance.

• Who is Gregor Mendel?

Scientists who studied inheritance in pea plants.

Why did he study pea plants?

He knew that there were male and female parts on

the plants. He also knew they could self pollinate

or cross pollinate.


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Genes and Dominance

Genes and DominanceA trait is a specific characteristic that varies from one individual to another.

Mendel studied seven pea plant traits, each with two contrasting characters.

He crossed plants with each of the seven contrasting characters and studied their offspring.

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Genes and Dominance

Mendel’s Seven F1 Crosses on Pea PlantsMendel’s F1 Crosses on Pea Plants

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Genes and Dominance

Each original pair of plants is the P (parental)

generation.

The offspring are called the F1, or “first filial,”

generation.

The offspring of crosses between parents with different

traits are called hybrids.

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Mendel's F2 Generation

P GenerationF1 Generation

Tall Tall Tall Tall Tall TallShort Short

F2 Generation

Segregation

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NOTES

Generations Genotype Phenotype Punnett Square Example


Parent

F1

F2

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Genes and Dominance

Mendel's Conclusions:

1. Principle of Independent Assortment:

Traits do not pass together.

Example: Yellow wrinkled or Green wrinkled

2. Principle of Dominance:

Some alleles are dominant while others are recessive.

Dominant always shows over recessive trait.

3. Principle of Segregation:

Traits separate during the formation of gametes. Meiosis!

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Segregation

Alleles separate during gamete formation.

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Genetics and Probability

Genetics and Probability

Probability The likelihood that a particular event will occur.

The principles of probability can be used to predict the outcomes of genetic crosses.

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Punnett Squares

Punnett Squares

Punnett square The gene combinations that might result from a genetic cross can be determined by drawing a diagram.

Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

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Notes

• Let’s go to your notes to look at human genotypes

and phenotypes.

• Then work on Punnett Square Examples


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NOTES

REMEMBER from your vocabulary:

• Homozygous –

• Heterozygous –

• Phenotype –

• Genotype –


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NOTES


Monohybrid Cross Examples

Genotypes

Phenotypes

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NOTES



Genotypes

Phenotypes

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NOTES



Genotypes

Phenotypes

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Independent Assortment

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 alleles for round (R) and

yellow (Y) are dominant over

the alleles for wrinkled (r) and

green (y).

The Punnett square predicts a

9 : 3 : 3 :1 ratio in the F2

generation.

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

F2 generation.

Represents:


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• Dimples and the ability to roll your tongue are both dominant traits.

Cross a man who is heterozygous for dimples and cannot roll his tongue

with a woman who does not have dimples but is homozygous dominant

for tongue rolling.

• Key:

• Cross:


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11–3 Exploring Mendelian Genetics

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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.

BLEND – RED + WHITE = Pink

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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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Incomplete dominance

• Try to cross 2 pink snapdragons.

• Cross:


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Codominance

Codominance

In codominance, both alleles contribute to the phenotype.

BOTH SHOW = BLACK + WHITE = SPECKLED

In certain varieties of chicken, the allele for blackfeathers is codominant with the allele for whitefeathers.

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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Codominance

• A black cat crossed with an orange one results in a

striped condition know as tortoise-shell. If two

tortoise-shell cats should mate, what would be the

genotypic and phenotypic outcome?

• Key:


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Multiple 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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Multiple Alleles

• A man with blood type AB marries a woman with

blood type O. Work out the possible blood types of

their offspring.

• Cross: IA IB x ii


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Multiple Alleles

• Work out the possible blood types of the offspring

according to a cross between a parent who is AO

and BO Blood.

• Cross: IAi x IBi


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14–2 Human Chromosomes

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Sex-Linked Genes

Sex-Linked Genes

The X chromosome and the Y chromosomes

determine sex.

Genes located on these chromosomes are called

sex-linked genes.

More than 100 sex-linked genetic disorders have

now been mapped to the X chromosome.

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14–2 Human Chromosomes

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Sex-Linked Genes

Possible Inheritance of

Colorblindness Allele

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Sex Linked Crosses

• Eye color is a sex-linked trait in fruit flies carried on the X chromosome

– R for dominant red and r for white. Determine the sex and eye color

for a father who has white eyes and mother who is homozygous

dominate for red eyes.

• Cross:


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Multiple Alleles

• Hemophilia is a recessive sex linked disorder that is carried on the X

chromosome - h for hemophilia and H for normal blood clotting. Cross a

father who has hemophilia with a mother who is a carrier (heterozygous)

for the disease, but does not show symptoms for hemophilia.

•

• Cross:


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Lab Problems

Punnett Squares Lab

REMEMBER – Use the examples we just created in class to help you

complete the lab problems.

Lab problems will be due at the end of class on Wednesday Feb 21.


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- or -

Continue to: Click to Launch:

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11-1

Resources/ch11_sectn01_quiz.qtb



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11-1

Gametes are also known as

a. genes.

b. sex cells.

c. alleles.

d. hybrids.

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11-1

The offspring of crosses between parents with

different traits are called

a. alleles.

b. hybrids.

c. gametes.

d. dominant.

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11-1

In Mendel’s pea experiments, the male gametes

are the

a. eggs.

b. seeds.

c. pollen.

d. sperm.

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11-1

In a cross of a true-breeding tall pea plant with a

true-breeding short pea plant, the F1 generation

consists of

a. all short plants.

b. all tall plants.

c. half tall plants and half short plants.

d. all plants of intermediate height.

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11-1

If a particular form of a trait is always present

when the allele controlling it is present, then the

allele must be

a. mixed.

b. recessive.

c. hybrid.

d. dominant.

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