Download Chapter 11

Chapter 11
Exit Slip Questions

Did Mendel cross-pollinate F1 plants to get
F2?

Was the recessive allele for shortness lost in
the F1 generation?

Are the F1 plants true-breeding?
I. Introduction to Genetics

Gregor Mendel


Known as the “father” of genetics
Garden Peas



Seven characteristics
Each characteristics occurred in two contrasting traits
Self-pollination and Cross-pollination

P generation is true-breeding, which would
produce identical offspring if allowed to selfpollinate.

F1 generation and F2 generation

Resulted in hybrids, which are a cross between 2 parents
with different traits.
Mendel’s Conclusions

Biological inheritance is determined by
factors that are passed from one
generation to the next. (Today’s
scientist call the chemical factors that
determine traits genes)

Each of trait Mendel studied by controlled
by 2 alleles, or different forms of the
same gene.
Continued…

Principle of Dominance

Some alleles are dominant and others are
recessive.

Recessive traits are only expressed when two
recessive alleles are the same characteristics are
present.


Represented by lower-case letter.
Dominant traits are fully expressed when on
either both or just one allele is present for a given
characteristic.

Represented by a Upper-case letter.
II. The Laws of Heredity

The Law of Segregation


A pair of factors is segregated, or
separated, during the formation of
gametes.
The Law of Independent
Assortment

Factors separate independently of one
another during the formation of gametes.
End of Section 1
III. Introduction to Genetic
Crosses

Genotype and Phenotype



Genotype is genetic makeup of an organism.
Phenotype is the organism’s appearance
Homozygous and Heterozygous


Homozygous means that both alleles of a pair is
alike. Both dominate or both recessive
Heterozygous means that the two alleles in the
pair are different. One dominate and one
recessive.

Complete dominance is when one allele is
completely dominant over another.

Incomplete dominance is when the
phenotype of the F1 generation is an
intermediate between that of the parents.

Codominance occurs when both alleles for
a gene are expressed in a heterozygous
offspring.
IV. Probability

The likelihood that a specific event occurs.

The principles of probability can be used to
predict the outcome of genetic crosses.

Probability = number of times an event is
expected to happen divided by number of
times an event could happen.
V. Monohybrid Crosses and
Dihybrid Crosses

Monohybrid Cross is a cross in which
only one characteristic is tracked.


Produces monohybrids
Dihybrid Cross is a cross in which two
characteristics are tracked.

Produces dihybrids
VI. Punnett Squares

A diagram used to aid in predicting the
probable distribution of inherited traits in the
offspring.

Uses capital and lower-case letter to represent
characteristics.

Genotypic ratio is the ratio of the
genotypes that appear in the offspring.

Phenotypic ratio is the ratio of the
offspring’s phenotype.
A. Monohybrid Crosses and
Punnett Squares



Homozygous X Homozygous
Homozygous Round Seeded Plant (RR) X Homozygous
Wrinkled Seeded Plant (rr)
R
R
r
Rr
Rr
r
Rr
Rr
Results:


Genotypic Ratio: 0 RR: 4 Rr: 0 rr OR 100% Rr
Phenotypic Ratio: 4 round: 0 wrinkled OR 100% round


Homozygous X Heterozygous
Homozygous Black Guinea Pig (BB) X Heterozygous Black
Guinea Pig (Bb)
Results:


B
B
B
BB
BB
b
Bb
Bb
Genotypic Ratio: 2 BB: 2 Bb: 0 bb OR 50% BB and 50% Bb
Phenotypic Ratio: 4 black: 0 not black OR 100% black



Heterozygous X Heterozygous
Heterozygous Black Guinea Pig (Bb) X Heterozygous Black
Guinea Pig (Bb)
B
b
Results:


B
BB
Bb
b
Bb
bb
Genotypic Ratio: 1 BB: 2 Bb: 1 bb OR 25% BB and 50% Bb and
25% bb
Phenotypic Ratio: 3 black: 1 not black OR 75% black and 25%
brown
B. Testcross

An individual of an unknown genotype
is crossed with a homozygous recessive
individual.

Determines the genotype of any
individual whose phenotype expresses
the dominant trait.