Transcript Mendel`s Theory

Mendel’s Theory
Mendel: The man, the myth ,
the legend
Mendel’s Hypotheses

Mendel found that there are two separate
“heritable factors” for each trait
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Alleles
Mendel’s Findings in Modern Terms
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Dominant alleles
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Recessive alleles
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Homozygous
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Heterozygous
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Genotype
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Phenotype
Laws of Heredity
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Law of Segregation


The two alleles for a trait segregate when
gametes are formed
Law of Independent Assortment
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Found that inheritance of one trait does not
influence inheritance of any other trait
Punnett Squares

A diagram that
predicts the expected
outcome of a genetic
cross

The cross of a long-stem (LL or Ll) and
short-stem (ll) plants involves a single
pair of alternate characteristics. Give the
genotype and phenotype ratios of the F1
generation when a homozygous long-stem
plant is crossed with a short stem plant.

Cross plants from the F1 generation in the
above problem and determine the
genotype and phenotype ratios of the F2
generation.
Problem

In pea plants, inflated pods are dominant to
constricted pods. Show the cross between a truebreeding inflated pod plant with a true-breeding
constricted pod plant. What are the expected
phenotypes and in what proportion?
Problem

In goats, a recessive gene causes the goats to
"faint" when they are startled. A farmer breeds
two goats (that have never fainted) and their first
offspring faints two days after its birth. What must
the parent's genotypes have been? Show the
cross to prove it.
Determining Unknown Genotypes
Perform a test cross

An organism with an unknown genotype is
crossed with a homozygous recessive
individual
Example

A pea plant with
yellow seeds has an
unknown genotype.
It is crossed with a
plant with green
seeds.
y
y
y
y
Y
Y
Yy
Yy
Yy
Yy
Y
y
Yy
yy
Yy
yy
Dihybrid Problem
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In peas, the allele for tall (T) plants is dominant to
the allele for dwarf (t) plants and the allele for
round (R) peas is dominant to that for wrinkled (r)
peas.
Find both phenotypic for the results of the following
cross:
TtRr x
TtRr
Dominant or Recessive?
Family Genetics