Transcript Genetics

GENETICS
June 2, 2016
I. IMPORTANT GENETICS VOCABULARY
A. Heredity: the passing on of
characteristics from parents to offspring
1. Example: eye color
B. Trait: characteristic that is inherited
1. Example: blue, brown, green eyes, etc.
C. Gene: A region of DNA that controls a
hereditary characteristic
1. Let’s do an example:
a. Let’s take the gene for hair color
b. How many different genes are present in
this room?
D. Alleles: Different forms of genes
1. For the gene for hair color how many
different alleles do each of you have?
a.
2
E. Phenotype: the way an organism looks
physically
F. Genotype: the gene combination an
organism has
1. Homozygous: an organism’s 2 alleles are
the same
a.
We call this a purebred
b.
2 capital letters would be homozygous
dominant
Problem: You can’t
1.
Give me an example
always know an
organism’s genotype
c.
2 lowercase letters would be
simply by looking at
homozygous recessive
its phenotype
1.
Give me an example
GENOTYPE (CONT.)
2.
Heterozygous: An organism’s 2 alleles for a trait
are different
Give me an example
 These are called hybrids

Homozygous
Heterozygous
II. WHERE DID IT ALL BEGIN?
A. Gregor Mendel (18221884)
1. Mendel was an
Austrian monk
2. Used pea plants to
study the
inheritance of traits
B. MENDELIAN VOCAB

1.
Mendel looked at plants over generations, so lets
give each generation a name…
PARENTAL GENERATION (P1)
a. These are the first two pea plants crossed.
b. Pea plants can SELF FERTILIZE so
sometimes both parents are the SAME plant!!
MENDELIAN VOCAB (CONT.)
2. The offspring of the parental generation are called
the 1st filial generation (F1)
P
F1
3. If we then cross plants from the F1 generation, we get
an F2 generation (2nd filial) and so on…
C. MENDEL’S EXPERIMENT
1.
Mendel took two pea plants that were identical in every
way except for their height, one was short and one was
tall.
2.
What is this generation called?

P1
3.
He cross pollinated them and took a look at
their offspring.
4.
When he planted the seeds from the cross
pollination the plants that were produced were
all tall.
5.
As you recall, this was his F1 generation
a.
FYI: Filial is Latin for son or daughter
6.
Next, Mendel allowed the tall plants in the F1
generation to self pollinate. He then planted
these seeds and grew 1000 plants.
7.
Mendel found in this F2 generation that ¾ of
the plants grew tall and ¼ were short.
8. WHY WAS THIS A BIG DISCOVERY FOR
MENDEL?
a.
1 trait of a pair seemed to disappear in the F1
generation, only to reappear unchanged in ¼ of
the F2 plants.
E. MENDEL’S CONCLUSIONS
1.
2.
Gregor Mendel didn’t know much if anything about
DNA or what it was, and he didn’t even know how
much you know…so what was Mendel’s big
conclusion after seeing his offspring?
He figured out that each organism must have 2
factors that control each of its traits.
III. MENDEL’S LAWS
A. Law of Dominance: In a heterozygous individual,
the dominant allele will be expressed and the
recessive allele will be hidden
B. Law of Segregation: During meiosis, homologous
pairs are separated and each gamete only receives
one allele
C. Law of Independent Assortment: During
meiosis, homologous pairs separate RANDOMLY
and INDEPENDENTLY of each other
IV. THE RULE OF DOMINANCE
A. In Mendel’s F1 offspring plants, there were only
tall plants even though one of the parents was
a short plant.
B. 1 of the alleles is dominant over the other.
C. The observed trait is DOMINANT and
the trait that disappeared is recessive.
1. In Mendel’s example which is the
dominant trait and which is the
recessive trait?
2. The allele for tallness is DOMINANT
3. The allele for shortness is recessive
HOW MANY OF YOU HAVE 6 FINGERS ON
EACH HAND?

6 fingers are dominant
HOW MANY OF YOU HAVE A WIDOW’S
PEAK?

Widow’s peak is dominant
HOW MANY OF YOU HAVE ATTACHED EAR
LOBES?

Attached earlobes are recessive
HOW MANY OF YOU HAVE THE ABILITY TO
ROLL YOUR TONGUE?

Rolling your tongue is dominant
HOW MANY OF YOU HAVE A STRAIGHT
THUMB?

Straight thumb is recessive
HOW MANY OF YOU HAVE BLUE EYES?

Blue eyes are recessive
HOW MANY OF YOU HAVE FRECKLES?

Having freckles are dominant
HOW MANY OF YOU HAVE A CLEFT CHIN?

Having a cleft chin is recessive
HOW MANY OF YOU HAVE A SECOND TOE
LONGER THAN YOUR BIG TOE?

Having a longer second toe is dominant
WHICH WAY DO YOUR THUMBS CROSS EACH
OTHER WHEN YOU ARE CLASPING YOUR HANDS
TOGETHER?

Left thumb on top is dominant
HOW MANY OF YOU HAVE AN IMMUNITY TO
POISON IVY?

Poison ivy immunity is dominant
THE RULE OF DOMINANCE (CONT.)
D.
We label or designate alleles with letters.
1. For example, a letter T for the trait of
height
2. An uppercase letter is used for the
dominant allele (T for tall)
3. A lowercase letter is used for the
recessive allele (t for short)
V. MENDEL’S LAW OF SEGREGATION

A.
What happens during Meiosis?
Mendel’s law of segregation
explains the results of his cross
between F1 tall plants. He
concluded that the 2 alleles for
each trait must separate when
sex cells are formed. A parent,
therefore, passes on at random
only one allele for each trait to
each offspring.
LET’S REVISIT MEIOSIS AGAIN

What happens in Metaphase 1

The law of independent assortment
Genes for different traits (for example seed shape
and seed color) are inherited independently of
each other.
 In our class example we used hair color


We saw depending on how homologous pairs
randomly lined up with each other that you could
tons of different combinations.
VI. PUNNETT SQUARES
A. In 1905, Reginald Punnett, an
English biologist, devised a way
of finding the expected
proportions of possible genotypes
in the offspring of a cross.
B. If you know the genotypes of the
parents, you can use a Punnett
square to predict the possible
genotypes of their offspring.
C. MONOHYBRID CROSS
1.
2.
Let’s consider Mendel’s first monohybrid cross
between his true-breeding Tall plants and his
true-breeding short plants. (P1  F1)
Each letter (allele) separates into a possible
gamete (sex cell).
t
t
T
Tt
Tt
T
Tt
Tt
3. MENDEL’S SECOND MONOHYBRID CROSS
a.
Now let’s look at Mendel’s second monohybrid
cross between his heterozygous F1 generation
self-pollinating themselves. (F1  F2)
T
t
T TT
Tt
t
tt
Tt
D. PROBABILITY
1.
Punnett squares show all of the possible
combinations of gametes and the likelihood that
each will occur.
a.
2.
In reality, however, you don’t get the exact ratio of
results shown in the square. That’s because
genetics is like flipping a coin, meiosis leaves it up
to chance.
After completing a Punnett square you are able
to calculate the probabilities of what offspring
will be produced.