Download Chapter 8 - Jamestown Public Schools

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Heredity

The passing of traits from parents
to offspring

The traits you have resemble your parents
These traits can include

◦
◦
◦
◦
Eye color
Shape of Eyes
Color of your hair
Height

Gregor
Mendel



Mendel: Austrian Monk, Father of
Genetics
Genetics- branch of biology focusing
on heredity
Crossed pea plants, counted
offspring , analyzed data

Why are
pea
plants
useful for
genetics?

1. Traits exist in 2 opposing forms,
without intermediates

2. Have male and female
organs


Easily control mating (self- fertilization or crosspollination)
3. Small, grow easily and
quickly, produce many offspring

Monohybri
d Cross


Monohybrid Cross: Involves one
pair of contrasting traits
For Example:
◦ Crossing a plant with purple flowers and
a plant with white flowers
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True
Breeding
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Step 1: Mendel wanted to create a
“Parental generation” also called the
“P” generation
True Breeding: Self pollinated pea
plants so all the offspring would
display only one form of the trait
Ex: A purple flowering plant only
produces purple flowers
Why would this be important?
Mendel’s Study of Traits – Step
2
 F1
Generatio
n
 Step 2: Cross pollinated two P
generation plants (Purple and
White flowers)
 Called the offspring from the P
generation the F1 generation
(First)
 Results: All were purple
flowers

F2
Generation



Step 3: The F1 Generation self
pollinated.
The offspring from the F1 generation
was called the F2 generation
Results: Three purple flowers, one
white flower

What were the results of
the F1 Generation?

What were the results of
the F2 generation?

What should Mendel’s
conclusion be?

Give one reason why pea plants are
good subjects for genetic experiments

Why was it important that Mendel
performed true breeding for the P
generation?

What did Mendal call each
generation?

Mendel’s
Hypotheses

1. Individuals inherit 2 copies of
each gene (trait)- one from each
parent
◦ Gametes carry only one allele for each
inherited trait

2. Alleles- different contrasting
versions of each gene (one from
each parent)

Ex: Brown eyes vs. Blue eyes

Mendel’s
Hypothese
s


3. When 2 different alleles are
present the Dominant one is
expressed
4. Recessive- trait that’s not
expressed when the dominant allele
is present

Genetics
Terms

In the following gentoype which
letter represents the dominate
gene?

Which letter represents the recessive
gene?

Genetics
Terms

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Homozygous- 2 alleles of a gene
are the same
(PP or pp)
Heterozygous- if the 2 alleles for a
gene are different (Pp)
◦ Only the dominant allele is expressed
(masks the recessive allele)
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Genetics
Terms

Genotype- allele combinations
(genes)
◦ Ff- Heterozygous
◦ FF- Homozygous dominant
◦ ff- Homozygous recessive
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Phenotype: is the physical appearance of
the trait
Ex: If “B” equals brown eyes and the
genotype is Bb the phenotype (expressed
trait) would be Brown eyes
Whiteboards – Quick
Questions
 What would be the genotype for an
individual heterozygous for the “F” trait?
 Ff
 What would be the phenotype for an
individual whose genotype is Tt where T
is tall and t is short?
 Tall
Whiteboards – Quick Questions
 Give an example of a heterozygous trait
 Ex: Ff
 Give an example of a homozygous trait
 Ex: FF, ff
 What would be the genotype for an
individual heterozygous for the “F” trait?
 Ff
 What would be the phenotype for an
individual whose genotype is Tt where T
is tall and t is short?
 Tall
Laws of Heredity
 Law of
segregati
on
 1. Law of Segregation:
Allele’s separate during
meiosis to produce gametes
 F1 generation (zygote) has
allele’s for each trait by both
parents

Law of
Independent
Assortment
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2. Law of Independent Assortment:
Alleles of genes separate
independently of one another during
gamete formation
Ex: Alleles for plant height separate
independently of the alleles for
flower color
Results: The inheritance of one trait does
not influence the inheritance of another –
COMPLETELY SEPARATE

What is the Law of Segregation?

What is the Law of Independent
Assortment?

Identify the phenotypes of rabbits with the
genotypes Bb and bb, where B- black coat
and b- brown coat.