Transcript Mendelian Genetics - Kenton County Schools

Blending hypothesis
• Originally, organisms were thought to be a
blend of their parents’ characteristics.
• Pure-breeds were defined as organisms that
looked identical to their parents, and they
looked like their parents, etc.
• So now, using these two pieces of information,
pretend you are a young scientist in the early
1800’s. You cross a purebred red flowering
plant with a purebred white flowering plant.
What do you expect to find?
THE ACTUAL RESULTS…
Mendelian Genetics
Father of Modern Genetics
• Austrian monk, high
school teacher, and
part-time garden
keeper
• First to propose
biological inheritance of
traits
• Work not recognized
until after his death
• Knew nothing about
DNA
Why pea plants?
• It’s what he had
• Pea plants are true
breeding
• Gregor noticed that one
stock of seed would
produce only tall plants
and another only short
plants
Cross-pollination
P generation
Next, Mendel wanted to find out if the recessive
alleles had disappeared, orif were they still
present in the F1 generation.
VOCAB BREAK…
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Traits
Genes
Alleles
Genotype
Phenotype
Segregation
• Mendel crossed the F1
generation with itself
• He found that the
recessive traits
reappeared in some of
the F2 generation
• He proposed this was due
to two things: the
principle of dominance
and segregation of alleles
during formation of
gametes
Probability
• Mendel categorized and
counted the many
offspring of each of his
experiments.
• He noticed that each
time he repeated a
particular cross he
obtained similar results.
For example:
Every time he crossed two
plants that were
heterozygous for stem
height (Tt), about ¾ of
the offspring were tall
and ¼ were short.
Probability and Punnett Squares
• Punnett squares are
used to predict this
probability
• Monohybrid crosses can
be performed to
determine probability
of genotype for one
particular trait
Genotypes
AA
Aa
aa
Homozygous Dominant
Heterozygous
Homozygous Recessive
Law of Segregation
• Mendel crossed the F1
generation with itself
• He found that the
recessive traits
reappeared in some of
the F2 generation
• He proposed this was due
to two things: the
principle of dominance
and segregation of alleles
during formation of
gametes
Law of Independent Assortment
• Genes that segregate independently do not
influence each other’s inheritance