Download Mendel`s Genetics

Mendel’s Genetics
Gregory Mendel
1851
Gregory Mendel
Mendel became a monastery priest, high
school teacher, and gardener.
He became fascinated with the diversity of
his pea plants.
Gregory Mendel
Mendel discovered that there
were “purebred” peas for
each of the traits. In other
words, there were round
seeded plants that if bred
with other round seeded
plants always produced
round seeds.
Gregory Mendel
Wrinkled seeded plants that
with other wrinkled seeded
plants always produced
wrinkled seeds.
Etc. Etc.
Gregory Mendel
The curious thing was what
happened when two different
“purebred” plants were bred
together.
Mendel’s Conclusions
Mendel concluded a couple of things.
1.
Heredity
2.
Dominant vs. Recessive Traits
3.
Two sets of “genes”
4.
Hybrids
Heredity
Mendel concluded that when organisms such as peas reproduce, some traits
from the parents can be passed on to offspring. Traits that can be passed on
are considered heritable.
For example, the color of a pea plant is determined by heredity. Being green is
a heritable trait.
Heredity
Not all traits are heritable.
For example, if a pea plant is
dried out because it didn’t get
watered, that has nothing to
do with its parents.
Dominance
Mendel also concluded that the traits being passed on by parents can come in
forms that are dominant or recessive. Dominant traits are able to somehow
mask or hide recessive ones.
For example, having round seeds is a dominant trait since a purebred round
seeded pea plant crossed with a purebred wrinkled seeded plant produces only
round seeded offspring.
2 Genes
The challenge for Mendel was trying to come up with an explanation for why
the second generation of a purebred cross began to produce offspring that
showed the recessive trait once again.
2 Genes
The answer came in the ratio. Nearly every time he performed his experiment,
he found that ~25% of the F2 offspring had the recessive trait. That got him
thinking about….
MATH!!!
MATH!!!
MATH!!!
MATH!!!
MATH!!!
How can you explain it?
2 GENES!
If the round plant has 2 dominant genes for being round.
And the wrinkled plant has 2 dominant genes for being wrinkled.
Then...
In the first
generation,
every
offspring
would get a
dominant
and a
recessive
copy.
MATH!!!
But in the second generation,
1 out of every 4 offspring
would get 2 recessive genes!
Mendel showed that life is
mathematical and that every
individual must have 2 sets
of each code or gene.
Hybrids
Mendel used the term hybrids for plants that must contain a dominant and a
recessive gene that were able to produce both dominant and recessive
offspring.
Genetics
DNA wasn’t known to
have any effect on
inheritance until 1943
so Mendel didn’t know
how traits were passed
on, he was only able to
show the mathematical
way it works with
dominance and
recessivity.
Genetics
To make it easier to write out the genes of an organism, scientists came up
with a system of capital and lowercase letters.
Capital letters are used to represent dominant genes.
Lowercase letters are used to represent recessive genes.
Genetics
For example:
Black fur in rabbits is
dominant. This rabbit
is a purebred, so its
genotype is BB.
A genotype is the
genetic code.
A phenotype is the way
something looks.
Genetics
This white rabbit is
albino. Albinism is a
recessive trait.
That means its
genotype must be bb.
What’s its phenotype?
Genetics
What would the
offspring look like if
these two rabbits bred?
Genetics
What would the
offspring look like if
these two rabbits bred?
Why?
Punnett Square
The square
Mendel
came up
with is called
a Punnett
Square.
Punnett Square
The square
Mendel
came up
with is called
a Punnett
Square.
Uh oh!
2 of these bunnies are
allowed to breed. What
color will their babies
be? Why?