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GENETICS: Our Family Tree
It’s all Relative!
--Did you know we share
99.9% of our genes with
other humans?
--95% of our genes with
chimpanzees?
--92% of our genes with a
mouse?
--So was Dr. Seuss thinking
about genetics?
It’s all in the genes!
Genes
-- the unit of heredity
--carry the information
about our traits
--found in the
chromosomes
--pass trait information
from parent to offspring
Combination Platter
Egg + Sperm = YU
--You inherited 23
chromosomes from each
parent.
--Each of those
chromosomes contained
ALLELES.
--Allele = different form of
same gene.
--The combination of those
alleles = YU!
Who’s the daddy?
--Genetics is the study of
heredity.
--Gregor Mendel is the
father of genetics.
--He was a priest in a
monastery who enjoyed
gardening.
--He was interested in the
different characteristics
of pea plants (yuck ).
The Birds and the Peas
--Mendel cross-pollinated
2 purebred pea plants.
--He took the pollen from
one plant and fertilized
it with the other plant.
--WHY?
To see what he could
see – the characteristics
of the offspring!
Mendel’s Peas
--Mendel noticed the size
of pea plants varied.
--He wondered what
would happen if he
crossed purebred
plants?
--Purebred – Tall or Short
(no in betweens—ex.
mediums)
Mendel’s cross between tall pea plants yielded all tall pea plants.
His cross between small pea plants yielded all small pea plants.
Tall x Tall = Tall
X
Small x Small = Small
=
X
P
P
P
F1
=
P
F1
Mendel’s cross of tall plants with small
plants resulted in tall plants.
=
X
F1
P
P
Mendel then crossed the first
generation (F1) tall plants and the
results (F2) were 1 out of 4 Small.
F1
X
=
F2
F2 Second Generation
Mendelalian Genetics
--What did Mendel learn
from his experiments?
1) Alleles are different
forms of a gene.
2) Alleles are either
DOMINANT or
Recessive.
3) Phenotype = physical
characteristic shown is a
result of at least 2
alleles.
Mendelian Genetics
--DOMINANT allele is the
trait that ALWAYS shows
up in the Phenotype.
--DOMINANT allele is
ALWAYS represented by
a CAPITAL letter (T= Tall)
--GENOTYPE =
combination of alleles
--Purebred Tall Pea Plants
have GENOTYPE TT
--TT = HOMOZYGOUS
DOMINANT
--HOMOZYGOUS = SAME
--Both alleles inherited are
DOMINANT or the
same
Mendelian Genetics
--Recessive alleles are
weak and hidden by
dominant allele.
--Recessive alleles DO
NOT show up in
Phenotype UNLESS two
are together*.
--Recessive alleles are
represented by a lower
case letter
--Purebred short pea
plants have
GENOTYPE tt
--tt is HOMOZYGOUS
Recessive.
--Both alleles are
Recessive or the
same.
Mendelian Genetics
• So what was the
GENOTYPE of the
first generation Tall
plants from Slide 9?
• Tall x Small = Tall
• Tt = HETEROZYGOUS
Dominant
--HETEROZYGOUS = two
alleles are NOT the
same
--One allele is
DOMINANT the other
Recessive
--HETERO = different
--Phenotype =
DOMINANT trait
ALWAYS shows up
--Plants are tall.
Say What?
Do you know ….
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Gregor Mendel
Heredity
Trait
Genes
Cross Pollination
Alleles
GENOTYPE
Phenotype
Purebred
• HOMOZYGOUS
• HETEROZYGOUS
• DOMINANT
• Recessive
• How to write the
GENOTYPES ?
• P generation
• F1 generation
• F2 generation
To be continued . . .
Punnett Squares,
Codominance,
Probability,
and Blood Typing . .
OH MY!!!!