Download Mendel and Heredity PPT

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Gregor Mendel
• Gregor Mendel was born
in 1822 to peasant parents
in what is now the
Czech Republic.
• He became part of a
monastery and was
in charge of the
monastery’s garden.
• Mendel discovered the basic
principles of heredity by
breeding garden peas in
carefully planned experiments.
Mendel’s Experiments
•
Over time, Mendel
learned how to prevent
the self-pollination of the
pea plants.
•
Instead, Mendel
controlled the pollination
of plants by using an
artist’s brush. He
transferred the pollen
from one flower to the
flower of another
selected plant.
Mendel’s Experiments
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•
Mendel used this technique to breed pea plants with
specific characteristics.
•
Through a series of carefully designed experiments,
Mendel crossed plants with different traits to see what
traits the offspring would have.
•
These offspring are called hybrids – offspring of
parents with different traits.
Mendel’s Experiments: Traits Studied
Seed
Shape
Seed
Color
Pod
Shape
Pod
Color
Seed
Coat
Color
Plant
Height
Flower
Position
Axial
Round
Yellow
Smooth
Green
Gray
Tall
Terminal
Wrinkled
Green
Constict
Yellow
White
Short
In order to keep his experiments simple, Mendel decided
to study seven isolated traits within a pea plant.
Mendel’s Experiments: F1 Generation
P Generation
F1 Generation
•
•
•
•
One of Mendel’s first experiments crossed two plants with different
seed colors (Yellow & Green).
These plants are called the parental generation (P Generation).
The offspring were all called the 1st filial generation (F1 Generation).
The offspring (F1 Generation) of these parent plants all had yellow
seeds.
Mendel’s Experiments: F2 Generation
P1
F1
F2
• Next, Mendel crossed two plants from the F1 Generation
• The offspring from this cross are called the 2nd filial generation (F2 Generation)
• After taking careful count, Mendel noticed that most of the seeds in F2
Generation were still yellow, but a small number were green.
• After completing hundreds of more experiments with other traits, Mendel
found this ratio to be approximately, 3 to 1.
Mendel to Modern Heredity
1. Mendel stated that “factors,” which do not blend together,
control each trait of a living thing. Each parent contributes
one of these factors to their offspring. Today, we call these
factors genes.
2. A gene is a section of DNA that codes for one protein. Genes
are what control & produce traits. The genes Mendel studied
came in two forms (tall/short; round/wrinkled seeds;
yellow/green; etc)
3. Alternative forms of the same gene are called alleles
(yellow/green, wrinkled/smooth, etc).
4. Some genes are dominant and some are recessive. The
effects of a dominant allele are always seen if it is present.
The effects of a recessive allele is not seen when the
dominant allele is present.
Further Findings
•
So, each trait is controlled by a gene, and each gene has two
alleles.
•
If the two alleles are the same, they are said to be
homozygous. If they are different, they are referred to as
heterozygous.
•
Dominant alleles are represented with a capital letter, while
recessive alleles with a lower case letter.
YY
Yy
yy
Homozygous
Dominant
Heterozygous
Dominant
Homozygous
Recessive
The Rule of Dominance
• A dominant trait is the trait
that will always be
expressed if at least one
dominant allele is present.
• The dominant allele is
always represented by a
capital letter.
• A recessive trait will only be
expressed if both alleles are
recessive.
• Recessive traits are
represented by a lower case
letter.
Law of Segregation
• This principle states
that the alleles for a trait
separate when gametes
are formed. These
allele pairs are then
randomly united at
fertilization.
• Alleles are now known
to be found on copies of
chromosomes – one
from each parent.
Allele for purple flowers
Locus for
Flower-color
gene
Homologous
pair of
chromes
Allele for white flower
More Findings
These alleles are separated during the formation of an
organism’s reproductive cells (sperm and eggs). Then, when the
egg and sperm joined, each organism would have one allele from
each parent.
Yy
Yy
Y
y
Y
y
YY
Yy
Yy
yy
An Example
F1 Generation
F2 Generation
YY
FATHER
MOTHER
Yy
Yy
Yy
yy
• The law of dominance explained the heredity of the offspring of the
F1 Generation
• The law of segregation explained the heredity of the F2 Generation
Phenotypes & Genotypes
• Phenotype – the physical
appearance of an organism; the way
it looks (tall/ short, green/yellow,
blue or brown eyes, etc.)
• Genotype – The genetic
combination (combination of alleles)
of an organism
(i.e. – YY, Yy, yy)
– Homozygous – both alleles are
the same
– Heterozygous – each allele is
different
Pea pod phenotypes
YY
yy
Pea pod genotypes
Punnett Squares: Monohybrid Crosses
Punnett Squares are a
shorthand way of showing
how alleles behave and a
prediction of an expected
genetic outcome.
Tt
2.Place the genotype of one
parent across the top and
the genotype of the other
on the left side.
Tt
1.Draw a big square and
divide it into fours.
Punnett Squares: Monohybrid Crosses
3. Place one allele at the side or top of each square
4. Populate each square with the corresponding alleles
Tt
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T
TT
Tt
t
Tt
tt
Tt
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Questions
1. How many different genotypes are present in this generation?
2. How many tall plants are in this generation?
Tt
t
T
TT
Tt
t
Tt
tt
Tt
T
Questions
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