Download Mendel`s Breeding Experiments

Objectives
 Identify the investigator whose studies
formed the basis of modern genetics
 List characteristics that make the garden pea a
good subject for genetic study
 Summarize the three major steps of Gregor
Mendel’s garden pea experiments
 Relate the ratios that Mendel observed in his
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crosses to his data
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Many of your traits (physical
characteristics), including the color
and shape of your eyes, the texture of
your hair, and even your height and
weight, resemble those of your parents.
The passing of traits from
parents to offspring is called
heredity.
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Mendel’s Studies of Traits
Mendel’s Breeding Experiments
Austrian monk named Gregor
Johann Mendel.
Mendel 1st to develop rules that
accurately predict patterns of
heredity.
form the basis of genetics, the
branch of biology that focuses on
heredity.
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Mendel’s
Breeding
Experiments
Mendel
experimented
with garden pea
heredity by
cross-pollinating
plants with
different
characteristics.
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Useful Features in Peas
1. Traits of the garden pea exist in 2
forms.
2. Controlled mating- male and
female reproductive parts are
within the same flower
3. Small, grows easily, matures
quickly, and produces many
offspring
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Monohybrid cross -involves
one pair of contrasting traits
Example: crossing a plant with
purple flowers and a plant with
white flowers
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 Mendel carried out his experiments in three
steps:
Step 1 Mendel allowed each variety of
garden pea to self-pollinate for several
generations to ensure that each variety was
true-breeding for a particular trait; that is,
all the offspring would display only one
form of the trait. These true-breeding plants
served as the parental generation in
Mendel’s experiments. The parental
generation, or P generation-the first two
individuals that are crossed in a breeding
experiment.
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Parental Generation
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Step 2 Mendel then crosspollinated two P generation
plants- offspring called the first
filial generation, or F1 generation.
Step 3 Mendel allowed the F1
generation to self-pollinate-called
the second filial generation, or F2
generation.
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Mendel’s Results
 Each of Mendel’s F1 plants showed only
one form of the trait.
 But when the F1 generation was allowed
to self-pollinate, the missing trait
reappeared in some of the plants in the
F2 generation.
 For each of the seven traits Mendel
studied, he found a 3:1 ratio of plants
expressing the contrasting traits in the
F2 generation.
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Mendel’s 4 Hypothesis
1. For each inherited character,
an individual has 2 copies of the
gene, 1 from each parent
2. There are alternative versions
of genes – alleles
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3. When 2 different alleles occur
together, 1 may be completely
expressed & 1 may not affect
appearance
Dominate – trait expressed
Recessive – trait not expressed when
dominate allele present
4. Alleles for each gene separate
during gamete formation
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Homozygous – the 2 alleles for a
trait are the same
Heterozygous – the 2 alleles for a
trait are different
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Genotype – the alleles an
individual has for a trait (genes)
Phenotype – the physical
appearance of a gene, it is
determined by the genotype
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