Transcript Document

Introduction to
Genetics
Chapter 11
Genetics, the study of heredity, is
a broad area of science that
encompasses many of today's
fastest-growing fields, including
molecular biology and
biotechnology.
Modern genetics offers vast
potential for eliminating
diseases, developing
pharmaceuticals, increasing
food production, and removing
pollutants from the
environment.
The science of genetics also
raises many important moral,
legal, and ethical issues that
are widely debated.
What is the ultimate
thing you inherit
from your parents?
Your genes which
make you who you are!
Who is Gregor Mendel and what did
he contribute to biology?

Austrian monk in charge of the monastery
garden in Vienna
Who is Gregor Mendel and what did
he contribute to biology?
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He cross pollinated pea plants to look for
patterns.
Traits he studied in pea plants:
In summary:
The science of genetics was born in
1856… Gregor Mendel performed an
historic series of experiments on pea
plants, thus discovering the laws of
heredity.
•Although Mendel published a paper on
his work, it was largely ignored by the
nineteenth-century scientific community.
•Today, he is heralded as the "father of
modern genetics".
Mendel's laws of
heredity described
dominant and recessive
traits.
A dominant trait is one
that is expressed even
in the presence of other
genes for the same
trait.
(you can see it!)
When symbolizing dominant
traits, a capital letter is used.
T = tall
TT = tall pea plant
Tt = tall pea plant
A recessive trait is one
that is "masked" by
dominant traits, but is
expressed when two
recessive genes are
present.
When symbolizing recessive traits,
lower-case letters are used.
t = short
tt = short pea plant
In the first of Mendel's experiments, a
tall pea plant (TT) was crossed with a
short pea plant (tt). The result of this
cross was two tall pea plants (Tt).
P generation
F1 generation
When these second-generation plants were
crossed, the result was one tall (TT) homozygote,
or organism with two of the same gene for a
specific trait; two tall (Tt) heterozygotes, or
organisms with two different genes for the same
trait; and one short (tt) homozygote.
F1 generation
F2 generation
Mendel concluded
that tallness in pea
plants was a
dominant trait, and
shortness was a
recessive trait.
The offspring of crosses
between parents with
different traits are called
hybrids. (Tt are hybrids
because they were
crossed with TT and tt)
What is a gene?
Genes are the chemical factors that
determine traits…
 Living organisms get one gene from
mom and one gene from dad…
 You have a gene or genes that
determine the shape of your ears,
nose, feet…everything about you!

What is an allele and where are they
found?
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The different forms of a gene are the alleles.
They are found on the chromosomes (which is
where the genes are found)
The allele for a tall pea plant is T and the allele
for a short pea plant is t.
In summary:
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TT, Tt and tt is a gene for height in pea
plants.
T is an allele and so is t.
Tt
is an
This This
is analso
allele
allele!
Both alleles make up
a gene!
How to say TT, Tt and tt the correct
way:
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TT = homozygous tall (homozygous means
the alleles are the same)
Tt = heterozygous tall (heterozygous
means the alleles are different)
tt = homozygous short (homozygous mean
the alleles are the same)
Genetics and Probability
The likelihood that a particular event will
occur (or happen) is called probability.
 The principals of probability can be used to
predict the outcomes of genetic crosses.
 Gene combinations (what allele you get from
your mom and what allele you get from your
dad) that might result from a genetic cross
can be determined by drawing a diagram
known as a Punnett square.

Punnett squares can be used
to predict and compare the
genetic variations that at
will result from a cross.
In other words, it is a prediction of what
the offspring will be by looking at the
parents. It is written as a ratio or a
percentage.
Generations…P, F1,
and F2
P = is the parents
F1 = is the parent’s first
offspring
F2 = is the F1’s offspring
Let’s work a problem!!!!
1) Write a key
You can choose
your own letters
as long as they
look different in
lower and upper
case.
Key:
T=tall
t=short
Would S be
a good
letter?
No!!!
Neither
would C,
K, O, P,
U, V, W,
X, and Z
2) Write the
genotype of the
parents as a cross
and label them as
P (for parent
generation)
Key:
T=tall
t=short
TT x tt
P
What is genotype?
Genotype is the genetic make
up (letters!).
The terms homozygous and heterozygous
are used to describe the genotype.
3) Show what
alleles are
available from the
gametes of the
parents
Key:
TT x tt
T
T
t
T=tall
P
t
t=short
4) Draw a Punnett
Square (a box with
a plus sign in the
middle)
Key:
TT
x
tt
T T
t t
T=tall
t=short
5) Put the alleles of
the parents on the
Punnett square (put
the first parent’s
alleles on the side
and the second on
top)
T
T
Key:
TT
x
tt
T T
t t
t
t
T=tall
P
t=short
6) Combine the
alleles from above
and to the side to
make a gene in the
box and label the
box F1
Helpful
Hint:
Always put
the capital
letter first
then lower
case
second if
there is
one!
Key:
TT
x
tt
T T
t t
t
t
T Tt Tt
T Tt Tt
T=tall
P
t=short
F1
7) Now you will
write the genotype
and phenotype of
the F1 generation in
ratio form
Key:
TT
x
tt
T T
t t
t
t
T Tt Tt
T Tt Tt
T=tall
P
t=short
Genotype of F1:
4 Tt=heterozygous tall
Phenotype of F1 :
4
Tall
Phenotype
is what
the gene looks like or
appears
What percentage
to be.
of
offspring are tall?
Short? Homozygous
tall? Homozygous
short? Heterozygous
F1 tall?
8) Now lets cross
two pea plants from
the F1 generation to
show the probability
of the genotype and
phenotype of the F2
generation …you do
not have to write the
key over since it will
be the
same…simply
choose two from the
F1 to cross (they are
the same so it
should be simple)
Key:
TT
x
tt
T T
t t
T=tall
P
t=short
Genotype of F1:
t
t
T Tt Tt
T Tt Tt
4 Tt=heterozygous tall
Phenotype:
4 Tall
F1
9) Run through the
same steps as
before
Genotype of F2:
1 TT = homozygous tall
2 Tt = heterozygous tall
1 tt = homozygous short
Phenotype of F2:
3 tall
1 short
Key:
Tt
x
Tt
T t
T t
T=tall
F1
t=short
T t
T TT Tt
t Tt tt
What percentage of
offspring are tall?
Short? Homozygous
tall? Homozygous
short? Heterozygous
tall?
F2
Now try one on your own!
A is a dominant characteristic.
This bird has two genes for orange feathers.
Its genotype is AA.
a is a recessive characteristic.
This bird has two genes for blue feathers.
Its genotype is aa.
Cross a
homozygous
orange feathered
bird with a
heterozygous
orange feathered
bird.
Key:
A=orange
feathers
a=blue
feathers
Key:
Cross a homozygous orange
feathered bird with a heterozygous
orange feathered bird.
AA x Aa
A A
A a
A a
A AA Aa
A AA Aa
A=orange
feathers
P
a=blue
feathers
Genotype of F1:
2
AA = homozygous
orange
What
percentage
of
offspring
have orange
2
Aa = heterozygous
orange
Phenotypefeathers?
of F1:
blue? Homozygous
4 orange
orange? Homozygous
blue? Heterozygous
F1 orange?
How about one more!!! (the
answer is yes since you do
not have a choice…just
pretend you’re getting a
choice…then it is much
more fun!)
Key:
Cross a heterozygous orange
feathered bird with a homozygous blue
feathered bird.
Aa x aa
A a
a a
a a
A Aa Aa
a aa aa
A=orange
feathers
P
a=blue
feathers
Genotype of F1:
2
Aa = heterozygous
orange
What
percentage
of
offspring
have blue
2
aa = homozygous
orange
Phenotypefeathers?
of F1:
blue? Homozygous
2 orange
orange? Homozygous
2 blue
blue? Heterozygous
F1 orange?
Monohybrid Crosses
 Crosses
that involve only
one characteristic (the type
we’ve worked today!)
Monohybrid Cross Problems
And finally…
(your homework problems!)
1.
In aliens from space, some are
tall and some are short. Short
is dominant over tall. If an
alien that is homozygous short
is crossed with an alien that is
homozygous tall, what is the
phenotype and genotype of the
F1 and F2 offspring?
2.
In aliens from space, having
antennae is dominant over
having horns. If an alien that is
heterozygous with antennae is
crossed with an alien that is
homozygous horns, what
percentage of chance will the
offspring have horns? What
percentage will have
antennae?
3.
In aliens from space, having
antennae is dominant over
having horns. What is the
genotype and phenotype if the
parents are heterozygous?
Monohybrid Cross Problems
(your homework problems!)
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Due at the first of next class
Please work the problems on your
notebook paper
Remember communication is the key, so
ask if you need help!
Good Luck….
Now WORK!!!!
Answers to homework
problems!
1.
In aliens from space, some are
tall and some are short. Short
is dominant over tall. If an
alien that is homozygous short
is crossed with an alien that is
homozygous tall, what is the
phenotype and genotype of the
F1 and F2 offspring?
1.
In aliens from space, some are
tall and some are short. Short is
dominant over tall. If an alien that
is homozygous short is crossed
with an alien that is homozygous
tall, what is the phenotype and
genotype of the F1 and F2
offspring?
Genotype of F1:
4 Tt = heterozygous short
Phenotype of F1:
4 short
TT x tt
t t
Key:
P
T T
T=short
t=tall
t
t
T Tt Tt
T Tt Tt
F1
In aliens from space, some are
tall and some are short. Short is
dominant over tall. If an alien that
is homozygous short is crossed
with an alien that is homozygous
tall, what is the phenotype and
genotype of the F1 and F2
offspring?
1.
Genotype of F2:
1 TT = homozygous short
2 Tt = heterozygous short
1 tt = homozygous tall
Phenotype of F2:
3 short
1 tall
Tt x Tt
T t
Key:
F1
T t
T=short
t=tall
T t
T TT Tt
t Tt tt
F2
2.
In aliens from space, having
antennae is dominant over
having horns. If an alien that is
heterozygous with antennae is
crossed with an alien that is
homozygous horns, what
percentage of chance will the
offspring have horns? What
percentage will have
antennae?
2.
In aliens from space, having
antennae is dominant over having
horns. If an alien that is heterozygous
with antennae is crossed with an
alien that is homozygous horns, what
percentage of chance will the
offspring have horns? What
percentage will have antennae?
Genotype of F1 :
Aa x aa
a a
A a
Key:
P
A=antennae
a = horns
a a
A Aa Aa
a aa aa
2 Aa = heterozygous antennae
2 aa = homozygous horns
Phenotype of F1:
2 antennae
2 horns
% with horns?
50%
% with antennae?
50%
F1
3.
In aliens from space, having
antennae is dominant over
having horns. What is the
genotype and phenotype if the
parents are heterozygous?
3.
In aliens from space, having
antennae is dominant over
having horns. What is the
genotype and phenotype if
the parents are
heterozygous?
Genotype of F1:
Aa x Aa
T t
T t
P
Key:
A=antennae
a = horns
A a
A AA Aa
a Aa aa
1 AA = homozygous antennae
2 Aa = heterozygous antennae
1 aa = homozygous horns
Phenotype of F1:
3 antennae
1 horns
F1