Mendel and Autosomal Inheritance

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• Mendel and Autosomal Inheritance
• Complete Dominance

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Gregor Mendel (Born 1882)
An Austrian monk who was the first person to
observe different inherited traits such as color
and height using the reproduction of pea plants
Im a monk and I like peas, darn it !
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Pea Plant Flower
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Sexual Reproduction In Plants
In plants, fertilization is called pollination
(pollen from the male meets the female parts)

• Self-pollination occurs when a plant is allowed
  to pollinate itself
• Cross pollination Different plants

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Cross Pollination
Female excepts the pollen
Male Produces Pollen
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Mendels Experiments
He studied only one trait at a time to control
the variables
He called these traits factors
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Mendels Experiments
He would cross-pollinate plants with two
variations of one trait For example, this dwarf
plant was mated with this tall plant
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Mendels Experiments
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What does this tell us??
F1 Must carry the tall AND the short factors
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What else does this tell us????

• Traits are inherited from generation to
  generation

Also, a hybrid is the offspring that inherited
both the tall factor and the short factor
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Mendels Rules
Rule of Unit factors Two factors (one from
each parent) affect one trait in an individual
Rule of Dominance The observed trait is called
dominant and the trait that cannot be seen is
recessive
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Recall Chromosomes!!!!

• We now call Mendels factors genes and are
  found on chromosomes

• Remember!!! We have a total of46 chromosomes
• ½ from mom and ½ from dad

44 are called autosomal chromosomes and 2 are
called sex chromosomes (Xs and Ys)
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Alleles
We call the alternate forms of a gene alleles
Alleles inherited from the mother are in red.
Those inherited from the father in blue.
A Alleles aA are different, or alternate, forms
of the A gene

Homologues Same chromosome from each parent
Just different forms of alleles
D Alleles
T Alleles
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General Terms

• Genotype ? pair of alleles denoted by letters
• TT homozygous dominant (Upper Case)
• Tt heterozygous (hybrid, carrierthe
  recessive t is not expressed the T
  dominnates over the t the t cannot be
  seen
• tt homozygous recessive
• Phenotype ? how the alleles are expressed what
  it looks like such as tall and short or even a
  genetic disease or abnormality (like polydactyl
  fingers)

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Genotypes Combination of Alleles
Remember!! Combination of alleles denoted by
using a capital letter for dominant alleles and
lower case letters for recessive traits
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Genotypes and Phenotypes
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Dominant Recessive Heterozygous and Homozygous
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Mendels Principles
Principle of Segregation
What it means each gene has two copies (alleles)
and a parent will give only one copy to a child.
The other parent will give another copy, and thus
the child will receive two copies (alleles)
Segregation of alleles in the production of sex
cells
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Mendels Principles
Principle Independent Assortment Genes for
different traits may assort independently of one
another in gamete production ? Leads to genetic
diversity
What it means different genes are inherited
separately. For example, the gene which codes for
eye color is inherited separately from the gene
which codes for nose shape.
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Independent Assortment
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Punnett Squares

• Table that shows probability of offspring having
  a particular trait
• Shows a cross (mating)between a males gamete
  with the females

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Punnett Squares
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Punnett squares
Cross a male with a Female What are the
probabilities of the sexes of the babies?
X Y


X
XX
XY
X
XX
XY
Genotypic Ratio 2 XY to 2 XX ? 11 (50/50
chance) Phenotypic Ratio 2 Males to females ?
22 ? 11
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Monohybrid Cross (crosses only 1 trait)
Moms Genotype is Rr and her phenotype is Round
Dads Genotype is Rr and his phenotype is Round
R
r
RR
Rr
R
Rr
rr
r
Genotypic Ratio 1RR2Rr1rr ? ? Write
Homozygous Dominant 1st, then Heterozygous then
Homozygous Recessive.
Phenotypic Ratio 3Round1Wrinkled?31 ?
Dominant first then recessive
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Test Cross

• Determine the genotypes of a parent based on
  offspring.
• In a Test cross, cross an unknown genotype to a
  known recessive (below)

T
T
t
T
t
t
T
t
t
t
t
t
T
T
t
t
t
T
T
t
t
t
t
T
If half of the offspring are short and the other
half tall the unknown is Tt, heterozygous
If all offspring are tall the unknown Is TT,
homozygous dominant
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Practice Punnett Squares- Write the Genotypic and
Phenotypic Ratios

• Cross the following and determine the genotypic
  and phenotypic ratios
• Homozygous yellow pod (YY) with heterozygous
  yellow pod (Yy)
• 2 heterozygous tall plants (Tt)
• 1 plant with wrinkled seeds (rr) with a plant
  that is heterozygous for round seeds (Rr)
• A homozygous dominant purple flower (PP) with a
  homozygous white flower (pp)