Download Introduction to Genetics

Introduction to
Genetics
Chapter 11-1 Notes
The varied patterns of stripes on
zebras are due to differences in
genetic makeup. No two zebras have
identical stripe patterns.
Every living thing – plants, animals,
microbes & humans have a set of
characteristics inherited from its parents.
1.
2.
3.
4.
Genetics: Branch of biology that focuses on heredity.
Heredity: The transmission of genetic traits from
parent to offspring.
Gene: Small sections of DNA that code for specific
traits.
Trait: Specific characteristic that varies from one
individual to another.
Before scientists knew about DNA &
chromosomes heredity was a great mystery!
Gregor Mendel
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Austrian monk, the “Father of Genetics”
Studied heredity in garden peas (Pisum sativum)
First to develop rules that predict patterns of
heredity
Interested in genetics when he crossed two pea
plans with purple flowers and noticed the
offspring had white flowers.
Used “quantitative” methods to analyze results!
 He actually counted the offspring and studied
the numbers.
Gregor Mendel
1822 - 1884
Why Peas???
1.
Traits are easy to distinguish (tell apart)
* Flower color
* Seed color
* Seed shape
* Flower position
2.
3.
* Pod color
* Pod shape
* Plant height
Mating of pea flowers is easy to control
Pea plants are small, grow easily, mature quickly
and produce many offspring.
* You get a lot of results, quickly!!
Pea Plant Traits
What did Mendel do???
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Step 1: Used true-breeding plants
Produce offspring identical to themselves
 Similar to a “pure breed” dog
 Called these the P (parental) generation
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Step 2:
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Crossed two P
generation plants,
each with a different
trait.
Offspring called the
F1 generation
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Step 3:
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Allowed F1 generation
to self-pollinate.
Offspring called the
F2 generation
Pea Plant Pollination
Mendel’s Experiments
Mendel’s Results
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Monohybrid cross: Involves one pair of
contrasting traits.
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The offspring of crosses between parents
with different traits are hybrids
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Example: Cross a plant with purple flowers and a
plant with white flowers.
Carry the traits of both parents, but only show the
traits of one parent
Alleles: Different forms of the same gene
1 gene for plant height
 2 alleles: tall and short
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Mendel’s Conclusions
Biological inheritance is determined by genes
that are passed from one generation to the
next.
 Each of the traits Mendel studied was controlled
by one gene that occurred in two contrasting
forms.
 These different forms produced each of the
different traits.

For example, the gene for plant height occurs in one
form that produces tall plants and in another form
that produces short plants.
Mendel’s Conclusions
Principle of Dominance.

The Principle of Dominance states that some
alleles are dominant and others are recessive.
 An
organism with a dominant allele for a trait will
always exhibit that form of the trait.
 An organism with a recessive allele for a will
exhibit that form only when the dominant allele
for the trait is not present.
Law of Segregation
Mendel wondered...were the recessive alleles
disappeared, or were they still present in the plants?
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He determined that the
separation, or segregation,
of alleles occurred.
Two alleles for a trait
segregate from each other
so that each sex cell
(gamete) carries only a
single copy of each gene.
Law of Independent Assortment
After determining that the alleles segregate during
the formation of gametes, Mendel wondered if the
segregation of one pair of alleles affect the
segregation of another pair of alleles?
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Mendel found that the inheritance of one trait
had no effect of the inheritance of another trait.
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Example: The gene that determines flower color
has nothing to do with the gene that determines
plant height.
concluded that
experimented with
which is called
the
which is called
the
which is called
the
Gregor
Mendel
concluded
that
experimented
with
Pea
plants
“Genes”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
Alleles are
separated during
gamete formation
which is
called the
which is
called the
Law of
Dominance
Law of
Segregation
Inheritance of
one trait has no effect
on the inheritance
of another trait
which is
called the
Law of
Independent
Assortment