Transcript Chapter 11.1-11.2 Genetics

Chapter 8
Mendel and Heredity
Why It’s Important
Knowledge of heredity
explains why you inherit
certain genes that affect
your…
appearance
________________,
________________,
behavior
and _____________
health
What characteristics are
important for this show
jumper to inherit?
Speed, strength, size
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Chapter 8
Section 1 The Origins of Genetics
8.1 Objectives
• Identify the investigator whose studies formed the basis
of modern genetics.
• List characteristics that make the garden pea a good
subject for genetic study.
• Summarize the three major steps of Gregor Mendel’s
garden pea experiments.
• Relate the ratios that Mendel observed in his crosses to
his data.
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Chapter 8
Section 2 Mendel’s Theory
8.2 Objectives
• Describe the four major hypotheses Mendel
developed.
• Define the terms homozygous, heterozygous,
genotype, and phenotype.
• Compare Mendel’s two laws of heredity.
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New Vocabulary
8.1 Vocabulary
• Heredity
• Genetics
• Monohybrid cross
• True-breeding
• P generation
• F1 generation
• F2 generation
8.2 Vocabulary
• Allele
• Dominant
• Recessive
• Homozygous
• Heterozygous
• Genotype
• Phenotype
• Law of Segregation
• Law of Independent
Assortment
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Chapter 8
Section 1 The Origins of Genetics
Mendel’s Studies of Traits
• Many of your _____________,
traits
including the color
and shape of your eyes, the texture of your hair, and
even your height and weight, ________________
resemble
those of your parents.
• The passing of traits from parents to offspring is
called _________________.
heredity
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• Long before the discovery of _______
DNA and
________________,
humans began experimenting
chromosomes
with heredity
• From the beginning of recorded history, humans have
crop
attempted to alter __________
plants and
______________
animals to give them traits that are
domestic
more useful to us.
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Chapter 8
Section 1 The Origins of Genetics
Mendel’s Breeding Experiments
• The scientific study of heredity began
more than a century ago with the work
of an Austrian monk named Gregor
Johann ________________.
Mendel
• The hereditary patterns that Mendel
discovered form the basis of
genetics
_______________,
the branch of
biology that focuses on heredity.
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• Mendel repeated experiments carried out earlier by a
Knight
British farmer named T. A. ___________,
who
crossed purple and white pea plants
mating
• The term cross refers to the _____________
or
____________
of two individuals
breeding
• Mendel’s experiments differed from Knight’s because
counted the number of each kind of
Mendel ___________
analyzed
offspring and _______________
the data
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Chapter 8
Section 1 The Origins of Genetics
To control breeding,
Mendel cut out the
male reproductive
anthers
organs, the ________
from one flower in the
cross
pistil
anthers
Only the female
reproductive organ,
pistil
the ___________,
remained
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Chapter 8
Section 1 The Origins of Genetics
Mendel then used a
brush to transfer the
male gamete,
commonly called
pollen
______________
to
the ___________
pistil
of
another flower
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Chapter 8
Section 1 The Origins of Genetics
Useful Features in Peas
• The garden pea was a good subject for studying
heredity for several reasons:
two
1. Several traits of the garden pea exist in ________
clearly different forms.
2. The male and female reproductive parts of garden
peas are enclosed within the _________
flower. This
same
self
allows cross pollination or ________
pollination
small
3. The garden pea is _________,
grows easily,
matures quickly, and produces _____________
many
offspring.
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Chapter 8
Section 1 The Origins of Genetics
Traits Expressed as Simple Ratios
• Mendel’s initial experiments were ____________
monohybrid
crosses.
one
• A monohybrid cross is a cross that involves ______
pair of contrasting traits.
• For example, crossing a plant with purple flowers and
a plant with white flowers is a monohybrid cross.
color
– The single trait studied is flower ________
– What were the two contrasting forms?
purple and white
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Chapter 8
Section 1 The Origins of Genetics
Mendel carried out his experiments in three steps
Step 1
Mendel allowed each
variety of garden pea to
self
________-pollinate
for
several generations to
ensure that each variety
true
was _______-breeding
for a particular trait
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“True breeding” means that
all of a plant’s offspring
one
display only ________
form
of a trait.
These true-breeding plants
are considered
purebreds
_______________
and
parents
served as the ___________
P
or _____
generation in
Mendel’s experiments.
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Chapter 8
Section 1 The Origins of Genetics
Step 2
cross Mendel then _________
pollinated two P generation
plants that had _____________
contrasting
forms of a trait, such as purple
flowers and white flowers.
Mendel called the offspring of the
P generation the first
filial
_____________
generation, or
____
F1 generation.
filial = son or daughter in latin
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Chapter 8
Section 1 The Origins of Genetics
First Filial Generation
• What color flowers
did all of the F1
offspring have?
purple
• Are the F1 offspring
still purebreds?
No
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Chapter 8
Section 1 The Origins of Genetics
Step 3
Mendel allowed the F1
self generation to ______
pollinate.
He called the offspring
of the F1 generation
plants the second filial
F2
generation, or ____
generation.
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Chapter 8
Section 1 The Origins of Genetics
What two colors
showed up in the F2
offspring?
Purple and white
How many total F2
offspring did Mendel
analyze?
929
What color ratio did
they exhibit?
3 purple : 1 white
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• The reduced ratio is very close to __________
3:1
705 : 224
224 224
= 3.1: 1
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Chapter 8
Section 1 The Origins of Genetics
Mendel’s Crosses and Results
• Mendel repeated
this breeding
experiment with
six
________
other
traits and acquired
similar
______________
data
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Chapter 8
Section 1 The Origins of Genetics
In Summary Results
one form
• Each of Mendel’s F1 plants showed only ______
of the trait.
– What color were they? purple
• But when the F1 generation was allowed to selfpollinate, the missing trait _____________
reappeared in some of
the plants in the F2 generation.
– What was the missing color? white
• For each of the seven traits Mendel studied, he found
3:1
a _______
ratio of contrasting traits in the F2
generation.
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Chapter 8
Section 2 Mendel’s Theory
A Theory of Heredity
• Mendel correctly concluded from his experiments that
each pea has _______
two separate “heritable factors”
for each trait—one from each parent.
• When gametes (sperm and egg cells) form, each
receives only ______
one of the organism’s two factors
for each trait.
fuse
• But when gametes _______
during fertilization, the
offspring has two factors for each trait, one from each
parent. Today these factors are called __________.
genes
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Chapter 8
Section 2 Mendel’s Theory
Mendel’s Hypotheses
• The four hypotheses Mendel developed as a result of
his experiments now make up the Mendelian theory
of heredity—the foundation of genetics.
two
1. For each inherited trait, an individual has _______
copies of the gene—one from each parent.
different
2. There are ____________
versions of genes. Today
the different versions of a gene are called its
alleles
____________.
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Chapter 8
Section 2 Mendel’s Theory
Mendel’s Hypotheses
3. When two different alleles occur together, one of
expressed
them may be completely _______________,
while
the other may have no ________________
observable effect on
the organism’s appearance.
Mendel described the expressed form of the trait as
dominant
_______________.
The trait that was not expressed when the dominant
form of the trait was present was described as
recessive
____________________.
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Chapter 8
Section 2 Mendel’s Theory
Mendel’s Hypotheses
4. When gametes are formed, the alleles for each
segregate independently
gene in an individual ______________
one
of one another. Thus, gametes carry only ______
allele for each inherited trait. When gametes unite
during ________________,
they combine to create
fertilization
two alleles for each inherited
an individual that has _____
trait.
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Chapter 8
Section 2 Mendel’s Theory
Mendel’s Findings in Modern Terms
• Dominant alleles are indicated by writing the first
letter of the trait as a ____________
letter.
capital
• Recessive alleles are also indicated by writing the
first letter of the dominant trait, but the letter is
_______________.
lowercase
– Example: Purple is the dominant trait for the flower
color of pea plants…
P
• The dominant allele is written as ______
• The recessive allele is written as ______
p
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Chapter 8
Section 2 Mendel’s Theory
• If the two alleles of a particular gene present in an
individual are the __________,
the individual is said to be
same
homozygous
__________________
– The prefix homo- means the same
– An individual may be…
AA
• Homozygous dominant = _____
• Homozygous recessive = _____
aa
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Chapter 8
Section 2 Mendel’s Theory
• If the alleles of a particular gene present in an individual
different
heterozygous
are ______________,
the individual is _______________.
– The prefix hetero- means other or different
Aa
– A heterozygous individual is written as ______
dominant
• In heterozygous individuals, only the _____________
allele is expressed; the recessive allele is present but
__________________.
unexpressed
• What color flowers will the following pea plant have…Pp?
purple
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Chapter 8
Section 2 Mendel’s Theory
Mendel’s Findings in Modern Terms
• The set of alleles that an individual has is called its
_________________________.
genotype
• The physical appearance of a trait is called a
_____________________.
phenotype
alleles
• Phenotype is determined by which ____________
are present.
pp
– So if a plant has the genotype _____,
what
phenotype will it have?
white flowers
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Chapter 8
Section 2 Mendel’s Theory
The Laws of Heredity
• Mendel’s findings allowed him to write two laws that
accurately describe the behavior of chromosomes
during _____________
meiosis
• These laws are called…
– The law of __________________
segregation
– The law of ______________
independent ________________
assortment
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Chapter 8
Section 2 Mendel’s Theory
The Law of Segregation
• This law states that the two alleles for a trait
separate
segregate or _______________
when gametes are
formed
• The alleles segregate because they are found on
chromosomes
__________________
which separate as they are
gametes
passed on to _____________
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Chapter 8
Section 2 Mendel’s Theory
The Law of Independent Assortment
• This law states that the alleles of different genes
separate _______________
independently of one another during
gamete formation.
• Mendel based this law on the fact that for the traits he
studied, the inheritance of one trait did not
influence
________________
the inheritance of any other trait.
– So for example, the inheritance of one trait, such
height
as plant _____________,
did not affect the
inheritance of another trait such as flower
___________
color
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• Remember, that the chromosomes line up randomly
during metaphase ____
I of meiosis.
• As the chromosomes below separate, what traits
might a gamete contain ?
P p
Gamete 1 = PY
Flower color
Purple or white
Gamete 2 = py
Y y
Gamete 3 = Py
Seed color
Yellow or green
Gamete 4 = pY
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• When Mendel wrote his laws, chromosomes had
_______
yet been discovered…he also did not know
not
linked on chromosomes
that genes are ________
• Using the chromosomes below, if a gamete receives
the dominant P allele, what other allele will it receive?
G
P
p
G
g
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• Genes that are ______________
farther
away from each
other on a chromosome are more likely to cross over
without each other, while closer genes are
linked
___________
Y
y
Y
y
p
P
g
G
linked
P
p
G
g
cross over
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• So while crossing over, independent assortment, and
increase genetic
random fertilization all ____________
variation, gene linkage ____________
the number of
limits
possible gene combinations
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Objective 1
• Identify the investigator whose studies formed the
basis of modern genetics.
Gregor Mendel
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Objective 2
• List characteristics that make the garden pea a good
subject for genetic study.
Traits have 2 contrasting forms
Male and female reproductive parts
are in the same flower
Small, matures quickly, many offspring
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Objective 3
• Summarize the three major steps of Gregor
Mendel’s garden pea experiments.
Formed P gen. through self-pollination
Cross-pollinated P gen. to form F1
Allowed F1 to self-pollinate to produce F2
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Objective 4
• Relate the ratios that Mendel observed in his crosses
to his data.
3:1 F2 ratio indicated that one trait was
Dominant and one was recessive
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Chapter 8
Section 2 Mendel’s Theory
Objective 5
• Describe the four major hypotheses Mendel
developed.
Individuals contain two copies of each gene
There are alternative versions of genes called alleles
One allele may be dominant while the other is recessive
The alleles segregate when gametes are formed
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Chapter 8
Section 2 Mendel’s Theory
Objective 6
• Define the terms homozygous, heterozygous,
genotype, and phenotype.
same
alleles
allele
combination
Different
alleles
physical
appearance
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Chapter 8
Section 2 Mendel’s Theory
Objective 7
• Compare Mendel’s two laws of heredity.
The law of segregation states that…
alleles on separate chromosomes segregate
The law of independent assortment states that…
the inheritance of traits on one
chromosome does not affect the traits
on a different chromosome
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