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Mendel’s Work
• Gregor Mendel was a priest in the 19th century
who loved to garden.
• While tending his garden he wondered why
some plants had traits similar to their parents,
and some plants had different traits then
those of their parents.
• TRAIT: Each different form of a characteristic
that an organism can pass on to it’s offspring.
Mendel’s Work
• Mendel decided to study heredity. His
research would eventually earn him the nick
name “the father of genetics”.
• HEREDITY: the passing of physical
characteristics from parent to offspring.
• GENETICS: the scientific study of heredity.
Mendel’s Experiment
• Mendel started his experiments with purebred
plants.
• PUREBRED: an organism that is the offspring
of many generations that have the same trait.
(purebred short pea plants come from short
parents and short grandparents, and short
great grandparents) – It can be represented by
letters TT or pp (all caps or all lowercase)
Mendel’s Experiment
• Once Mendel had purebred plants, he cross
bred plants with different traits with one
another.
Mendel’s Experiment
• In Mendel’s experiments, he called plants in
the first cross the parental generation or P
generation.
• The offspring of the P genertation he called
the F1 generation.
• The offspring of the F1 generation he called
the F2 generation.
Mendel’s Results
P = Parent Generation
F = Daughter or Son 1st Generation
F = Daughter or Son 2nd Generation
Mendel’s Results
• In all of Mendel’s crosses only one form of the
trait appeared in the F1 generation, however,
in the F2 generation the lost form of the trait
always reappeared in about ¼ of the plants.
Dominant and Recessive Alleles
• GENE: A section of the DNA that codes for a
specific trait. (hair color gene)
• ALLELES: the different forms of a particular
gene. (brown or blonde)
• An organisms traits are controlled by the
alleles it inherits from it’s parents. Some
alleles are dominant while other alleles are
recessive.
These are alleles; different forms of a gene
cc – could be alleles for hair color
ee- could be alleles for spots
hH- could be alleles for straight hair
Dominant and Recessive Alleles
Dominant and Recessive Alleles
Dominant and Recessive Alleles
• A dominant allele is one whose trait always
shows up in the organism when the allele is
present. Represented by a Capital Letter(T)
• A recessive allele is one whose trait is hidden
when the dominant allele is present.
Represented by a Lower Cased Letter(t)
Inheriting Alleles and Symbols for Alleles (Purebred vs. Hybrid)
• For every trait you have, your DNA is carrying
2 alleles. One came from your mom and one
came from your dad.
• If both are the dominant version, you show the
dominant trait. Ex. TT (purebred)
• If both are the recessive version, you show the
recessive trait. Ex. tt (Purebred)
• If one is the dominant version and one is the
recessive version, you show the dominant trait.
Ex. Tt (Hybrid)
Inheriting Alleles and Symbols for Alleles (Purebred vs. Hybrid)
Purebred - Tall
Hybrid - Tall
Hybrid - Tall
Purebred - Short
In hybrid allele
combinations; if the
dominant allele is
present then that
trait will appear.
Recessive traits
only appear if both
recessive alleles
are present.
Phenotypes and Genotypes
• An organism’s phenotype is its physical
appearance or visible traits.
(tall, blonde, round seeds, brown eyes)
• An organism’s genotype is its genetic makeup
or allele combinations.
(Tt, bb, RR, Bb)
Genotypes
• An organism that has two identical alleles for
a trait is said to be homozygous.
RR= homozygous dominant
rr= homozygous recessive
• An organism that has two different alleles for
a trait is said to be heterozygous.
• Rr = heterozygous
Section 3
The Cell and Inheritance
• According to the chromosome theory of
inheritance, genes are carried from their
parents to their offspring on chromosomes.
The Cell and Inheritance
• Remember, humans have 46 chromosomes.
• Those chromosomes are in pairs. 23 come
from the father’s sperm, and 23 come from
the mother’s egg.
• When the sperm and egg come together, the
resulting offspring has all 46 chromosomes.
• Chromosomes in the same pair carry the same genes,
but not necessarily the same alleles.
• For example, pair #1 may have the mother’s hair color
gene on one chromosome, and the father’s hair color
gene on the other chromosome.
xx
23 pairs of chromosomes
(single copy of the DNA)
23 pairs of chromosomes
(duplicated DNA)
Meiosis
• How do sperm and eggs end up with only half
the number of chromosomes?
• Instead of dividing by MITOSIS, the parent
cells of sperm and eggs divide by a process
called meiosis.
Meiosis
• During meiosis the chromosomes pairs
separate and are distributed to two different
cells. The resulting cells have only half as
many chromosomes as the other cells in the
organism.
http://www.youtube.com/watch?v=1yu1Zuy
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http://www.youtube.com/watch?v=zglQ2Ild
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Meiosis
• When the chromosomes pairs separate and go
into two different sex cells, so do the alleles
carried on each chromosome.
• One allele from each pair goes to each sex
cell.
Please Take out your Foldable
• Put these Terms on the Back Side of your foldbable
– Probability = chance an event will occur
– Independence of Events = chances of one event do not
effect the outcome of the next event
– Punnett Squares = shows combinations of allele
possibilities
– Phenotype = physical characteristic
– Genotype = allele combination (Tt, Bb, hh, FF)
– Homozygous = TT (Dominant;purebred) tt(recessive;
purebred)
– Heterozygous = Tt (hybrid)
Mendel’s Results
P = Parent Generation
F = Daughter or Son 1st Generation
F = Daughter or Son 2nd Generation
Dominant and Recessive Alleles
Dominant and Recessive Alleles
• A dominant allele is one whose trait always
shows up in the organism when the allele is
present. Represented by a Capital Letter(T)
• A recessive allele is one whose trait is hidden
when the dominant allele is present.
Represented by a Lower Cased Letter(t)
Inheriting Alleles and Symbols for Alleles (Purebred vs. Hybrid)
• For every trait you have, your DNA is carrying
2 alleles. One came from your mom and one
came from your dad.
• If both are the dominant version, you show the
dominant trait. Ex. TT (purebred)
• If both are the recessive version, you show the
recessive trait. Ex. tt (Purebred)
• If one is the dominant version and one is the
recessive version, you show the dominant trait.
Ex. Tt (Hybrid)
Inheriting Alleles and Symbols for Alleles (Purebred vs. Hybrid)
Purebred - Tall
Hybrid - Tall
Hybrid - Tall
Purebred - Short
In hybrid allele
combinations; if the
dominant allele is
present then that
trait will appear.
Recessive traits
only appear if both
recessive alleles
are present.
DO NOW
• PLEASE FINISH FOLDABLE AT HOME
– USE MY ANSWERS
• Take out your foldable and glue the vocab
onto the back side of the last page
Section 2
Probability and Heredity
• Probability is a number that describes how
likely it is that an event will occur.
Probability
• Probability can be expressed as a fraction, or
as a percent.
• If you flip a coin, there is a one in two chance
it will land on heads…. ½, or 50%
• If you roll a dice, there is a one in six chance
you will roll a 5… 1/6, or about 17%.
Independence of Events
• When you toss a coin more than once, the
results of one toss do not affect the results of
the next toss.
• Flipping a heads the first time, does not make
you more likely to flip a tails the next time.
Probability and Genetics
Mendel realized that when he crossed
tall plant and a short plant, the
probability of the off spring in the F1
generation being tall was 4/4 or 100%
The probability of the offspring in the F2
generation being tall was ¾ or 75%
Punnett Squares
• A punnett square is a chart that shows all
possible combinations of alleles that can
result from a genetic cross.
Punnett Squares
Capital letters= Dominant allele
Lowercase letters= recessive allele
Ex. The allele for round seed is dominant over the allele for wrinkled seeds
R=round seeds
r = wrinkled seeds
T = Tall
t = short
COMPLETE THESE IN YOUR NOTEBOOK
T = Tall
t = short
Please Take out your Foldable
• Put these Terms on the Back Side of your foldbable
– Probability =
– Independence of Events =
– Punnett Squares =
– Phenotype =
– Genotype =
– Homozygous =
– Heterozygous =
Meiosis accounts for probability
S = Round Pea
s = Wrinkled pea
Ss = Round
Ss = Round
Words to Know
•
Homozygous – combination of alleles in which both are the same; both dominant
(TT) or both recessive (tt) – also known as purebred
•
Heterozygous – a combination of alleles in which both are different or hybrid;
dominant and recessive (Tt) - also known as hybrid
•
Phenotype – the actual physical appearance; tall, short, brown eyes, blue eyes,
based on the genotype
•
Genotype – the combination of alleles (TT, Tt, tt); these combinations
•
Dominant – Alleles that are dominant are represented by a capital letter (“T”) and
will always appear (in the phenotype) if they are present
•
Recessive – Alleles that recessive are represented by a lower cased letter (“t”) and
will be masked if a dominant alleles is present