What is genetics?
Born in 1822 in
Became a monk at a
monastery in 1843.
Taught biology and
had interests in
Also studied at the
University of Vienna
After returning to the
continued to teach
and worked in the
Between 1856 and
1863 he grew and
tested over 28,000
Easy to grow.
Easily identifiable traits
Can work with large numbers of
The first thing Mendel did was create a
“pure” generation or true-breeding
He made sure that certain pea plants
were only able to self pollinate,
eliminating unwanted traits.
He did this by cutting away the stamen,
or male part of each flower
Genes and dominance
Trait : a characteristic
Mendel studied seven of these traits
After Mendel ensured that his true-
breeding generation was pure, he then
crossed plants showing contrasting
He called the offspring the F1
generation or first filial.
What will happen when pure
yellow peas are crossed with
pure green peas?
All of the
Hybrids = the
What did Mendel
Inheritance is determined by factors
passed on from one generation to
Mendel knew nothing about
chromosomes, genes, or DNA. Why?
These terms hadn‟t yet been defined.
What were Mendel’s
The „factors” that Mendel mentioned
were the genes.
Each gene has different forms called
Mendel‟s second principle stated that
some alleles are dominant and some
Mendel’s second cross
He allowed the F1 generation to self-
pollinate thus producing the F2
Did the recessive allele completely
What happened when he crossed two
yellow pea hybrid (F1) plants?
¾ of the peas were yellow, ¼ of
the peas were green.
During the formation of the sex cells or
gametes, the alleles separated or
segregated to different gametes. (pollen
The likelihood of a
Can be expressed
as a fraction or a
Example: coin flip.
A diagram used to
show the probability
or chances of a
certain trait being
passed from one
Gametes are placed above and to the
left of the square
Offspring are placed in the square.
Capital letters (Y) represent dominant
Lower case letters (y) represent
Punnett square example
Homozygous = when an organism
possesses two identical alleles. ex.
YY or yy
Heterozygous = when an organism
possesses different alleles. ex.
Phenotype vs genotype
The genetic makeup Physical
Symbolized with appearance of the
Tt or TT Expression of the
Short, tall, yellow,
No one event has a greater chance of
occurring than another.
You cannot predict the precise outcome
of an individual event.
The more trials performed, the closer
the actual results to the expected
Punnett square review:
The two factor cross. Example: color
and shape of peas.
F1 cross to produce the F2 generation
Ex RRYY x rryy
Round yellow mated with wrinkled green
• Offspring would all be hybrid for both
What is independent
The dihybrid cross
Punnett square on board:
Mendel published his paper on heredity
The scientific community saw little if any
importance in his work.
Mendel died in 1884 with no recognition
for his contributions to genetics.
Some exceptions to
Some alleles are neither
dominant nor recessive.
Many traits are controlled by
more than one gene (polygenic
A situation in which neither allele is
When both alleles are present a “new”
phenotype appears that is a blend of
Alleles will be represented by capital
Red flower plant genotype = RR
White flower plant genotype = WW
Pink flower plant genotype = RW
What happens when a
red flower is crossed
with a white flower?
some white and
some red or all
red or white.
All are pink
When two alleles both appear in the
Usually signified using superscripts.
example: color of hair coat in cattle.
crcr = red hairs
cwcw = white hairs
crcw = roan coat (mixture of both colors)
Roan cattle inheritance
When two or more alleles contribute to
Human blood types: A,B,O and AB
A and B are codominant to each other.
Both A and B are dominant over O.
Human Blood types:
Allele = IA
antigens on the
Allele = IB
with type B
genotype = IAIB
types of antigens
Allele = i
No antigens on
the surface of
the blood cells
6 different genotypes
IAIA Type A
IAIB Type AB
IBIB Type B
IBi Type B
IAi Type A
ii Type O
How common are the
different blood types?
A man with type AB blood
marries a woman with type B
blood whose father has type O
blood. What are the chances
that they have a child with type
A blood? Type AB?
Traits controlled by two or more
eye and skin
Rediscovery of Mendel’s
Around the turn of the century (early
1900‟s) many scientists “rediscovered”
1908 – Garrod
1902 – Sutton
1910 – Morgan
Thomas Hunt Morgan
Born in Kentucky,
professor of Biology
at Columbia U.
Worked with fruit
Nobel Prize in
Why the Fruit Fly?
1. Can work with
large numbers of
2. Produce many
3. Short reproductive
4. Only four pairs of
A method of cell division similar to
2 main differences:
1. There are two divisions to produce 4
2. The cells produce contain ½ the
chromosomes as the original cell
All cells of an
organism contain a
specific number of
Most cells are
diploid (2n) meaning
they have two
copies of each
Events of meiosis I
During prophase I, each
chromosome pairs with its
homologous chromosome to
form a tetrad
Results in greater
Neither cell replicates its chromosomes.
Each cell splits (similar to mitosis)
Produces four daughter cells.
2 types: Spermatogeneis
4 mature sperm 1 mature ova or
Each sperm has egg.
exactly half the Each egg has
number of exactly half the
chromosomes as number of
the father. chromosomes as
Are genes “linked” to each other on
Morgan found that many genes are
It was determined that chromosomes,
not genes, assort independently during
by Sturtevant in
The farther apart
two genes are,
the more likely
they will be
1-10, 13, 14, 17, 18, 24