Heredity
What would you do if you
opened your eggs and
saw that some of them
were blue or green?
http://www.inspirationline.com/images/ArauEggs.jpg
Selective Breeding in
Agriculture
• For thousands of years farmers
have selective bread animals to
get the traits they want.
• Farmers mate one animal with
qualities they want with another
with qualities they want hoping to
get animals with both qualities.
• This the earliest form of Heredity.
– Heredity is the passing of traits from
parents to offspring.
Gregor Mendel 1822
• Mendel was a monk
from Austria
• He grew up on a farm
so he grew crops in
the monastery garden
• He was the first to use
plants to learn how
traits are passed from
one generation to
another.
http://www.xtec.es/~jllort1/biolegseuropa/mendel.jpg
Why peas?
• Peas grow relatively quickly
• Pease come in many varieties
• Pease are self-pollinating
– Self-pollinating= contains both male and female
reproductive structures and can fertilize itself or
another plant.
Mendel’s First Experiment
• Round crossed with Wrinkled
• The results:100% Round
• Does this surprise you? What
happened to the trait for wrinkled
seeds?
Mendel repeated this for
other traits…
• Mendel had similar results from
the other crosses he made
• One trait always appeared, then
the other trait seemed to vanish.
What happened to the
wrinkled seeds?
• Mendel allowed the first generation
from each of the seven crosses to
self-pollinate.
• He crossed two of the offspring
• In this second generation the trait
that disappeared reappeared.
• 3 of the offspring were Round and
1 was wrinkled.
Mendel’s Brilliant Idea
• Mendel concluded each plant had two
sets of instructions for each
characteristic.
• The fertilized egg would then have two
forms of the same GENE for every trait-one from each parent.
• The two forms of a gene are known as
ALLELES.
– Homozygous – two identical alelles(HH)
– Heterzygous – two different alelles(Hh)
But what about the
wrinkled ones?
• Traits can be expressed as dominant or
recessive.
• Dominant alleles mask the
expression of recessive alleles.
– They are written with a capital letter.
• Recessive alleles are only
expressed when there they are by
themselves.
– -They are written with a lower case
letter.
Peas, For Example,
• Round is dominant to wrinkled
• If an plant gets an allele for round
from its mother and an allele for
wrinkled from its father then the
plant will be round.
• If the dominant is present it masks
the expression of the recessive.
The Punnett Square
• A punnett square is used to
visualize all the possible
combinations of alleles from the
parents.
• Dominant alleles are symbolized
with capitol letters and recessive
with lowercase letters.
• Like algebra, you can use any
letter to symbolize a trait.
Birdie Example
• Blue bird crossed with a red
bird.
• Each box represents a
potential offspring.
• Remember meiosis? Half
from mom, half from dad?
Mom only has A and Dad
only has a to give.
• All offspring in this case will
be red because the A masks
the expression of the a.
Genotype vs Phenotype
• The inherited combination of
alleles is known as the
offspring’s genotype (the
letters).
– The genotype of the offspring is
Aa.
• They physical appearance of
the offspring would be RED as
this is the dominant allele.
What are the chances?
• Probability- the mathematical chance
that an event will occur
• Probability is usually expressed as a
percentage or fraction.
• Punnett square:
–
–
–
–
–
4 boxes
1 box blue
3 boxes red
3/4= red, 75%
1/4= blue, 25%
New Ideas…
• New ideas are often rejected.
• In 1865 Mendel published his
findings but was ignored by the
scientific community.
• 30 years after his death Mendel
finally got eh recognition he
deserved: Father of Genetics
Practice: Male or Female
What is the percent chance that the offspring will be male?
Practice: Peas
What is the percent chance that the flower will
be white? What % of the offspring will be
heterozygote?