Download Gregor Mendel and Genetics

Bellringer 11/5/13

What is the relationship
between DNA and the way you
look?
Topic: Introduction into
genetics
EQ: What is
genetics?
Genetic Material

The nucleus of a cell contains
genetic material
DNA chromosomes genes ->
Alleles
www.kent.edu/projects/cell/page7.htm
Who was Gregor Mendel
and what is genetics?



Gregor Mendel was an
Austrian monk in the
mid-nineteenth century.
He carried out the first
important studies of
heredity by using pea
plants.
Genetics is the branch
of biology that studies
heredity.
Inheritance

Occurs when traits are
passed down from
parent to child.
Traits


The different versions
of a characteristic
Example: blue, green,
and brown eyes
What is heredity?

Heredity is the passing on of characteristics
from parents to offspring.

The characteristics that are passed down are
called traits.
Gregor Mendel’s Monohybrid Cross
(p.156 in science book)
A monohybrid cross is when you cross two plants that differ only by
one trait.
1st Generation=
2nd Generation=
3rd Generation=
Tall Peas
X
short Peas
All tall Peas
¾ produced tall peas (75%),
¼ produced short peas (25%)
The Rule of Unit Factors



After seeing what happened Mendel concluded that
there are two factors that control each trait.
We now know that these factors are called genes.
Each gene has different forms that are called alleles.
One allele is inherited from each of the parents.
Genes and Alleles


Each chromosome
has information
about thousands of
traits
Gene- section on
chromosome that has
information for one
trait
See page 174
Genes

Genes are short
sections of
chromosomes
http://www.accessexcellence.org
What are Genes?
Factors that are passed from one generation to
the next…
Genes come in different forms called alleles:
ex: tall and short
Some are seen and some are not
Genes come in pairs

Since
chromosomes
come in pairs (one
from mom, one
from dad)

Genes come in
pairs
http://anthro.palomar.edu/biobasis/images/
karyotype_male.gif
The Rule of Dominance


When the offspring inherit two different alleles
for one trait, the trait that is expressed is said to
be dominant while the other is recessive.
In Mendel’s pea plants that had one allele for
tall and one allele for short, the peas were tall
because tall is the dominant trait.
Recessive
Dominant
Genes



Dominant: those traits that are seen
Recessive: those traits that are not
seen
Thus came the principle of
dominance: some are dominant
and others are recessive
Recessive allele
Recessive allele
Martin Sheen
Charlie Sheen
Talk about dominant genes!!!
Kirk
Kirk Douglas
Michael
Emilio Estevez
Activity


Cut out figure 3 pg. 166
Answer the Visual Check #7. Be sure to use
the terms dominant and recessive in your
answer.
Genotypes and Phenotypes

A Genotype is a specific combination of alleles.

A Phenotype is the visual trait that is expressed.
Tall Allele
Possible Generation= TT
Possible Genotypes= TT
short Allele
Tt
Tt
Tt
Tt
Possible Phenotypes= Tall, Tall, Tall, short
tt
tt
Homozygous and Heterozygous

An organism is homozygous dominant for a trait if both of the
alleles carry the dominant gene.
RR = Homozygous dominant (pure)

An organism is said to be homozygous recessive for a trait if
the alleles both carry the recessive gene.
rr = Homozygous recessive (pure)

An organism is heterozygous for a trait if the two alleles are
different.
Rr = Heterozygous (Hybrid)
1st Generation=
Tt
X
T
t
2nd Generation=
Tt
T
TT
t
Tt
Tt
tt
TT, Tt, Tt, tt
Genotype Ratio = 25% homozygous tall,
50% heterozygous tall,
25% homozygous short
Phenotype Ratio =
3 Tall, 1 short
Using Alleles in Mendel’s Experiment
Tall Allele
P1 Generation=
Short Allele
TT X tt
Punnett Square –
a tool used to visualize all the
possible combinations of alleles
from the parents
Genotype Ratio =
100% Tt (heterozygous Tall)
Phenotype Ratio =
100% Tall
0% short
t
Tt
t
Tt
T
T
Tt
Tt
Pea Plant Traits