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Exploring Mendelian
Genetics
CHAPTER 11 SECTION 3
SC B-46: PREDICT INHERITED
TRAITS BY USING THE PRINCIPLES
OF MENDELIAN GENETICS
(INCLUDING SEGREGATION,
INDEPENDENT ASSORTMENT, AND
TYPES OF DOMINANCE)
Essential Question
 How would you explain the inheritance
patterns beyond dominant & recessive?
Dihybrid Crosses
 Mendel also performed an experiment to
follow 2 different genes as they passed from
parents to offspring
 Mendel chose true-breeding round, yellow
peas crossed with true-breeding wrinkled,
green for F1
 (RRYY) x (rryy)
 What genotype/phenotype will the offspring
have?
Mendel’s 2nd Experiment
 The Inheritance of 2 Traits
 Does the inheritance of 1 characteristic
influence the inheritance of another
characteristic?
 For example: Does pea shape influence pea
color?
F1 Generation allowed to self-pollinate
Results:
 Mendel’s plants produced 556 seeds
 round & yellow: 315
 wrinkled & green: 32
 combinations of parent phenotypes: 209
 Mendel’s conclusion:
 Alleles for seed shape & color segregate
independently when gametes forming
Law of Independent Assortment
 Genes from different traits can segregate
independently during the formation of gametes.
 This accounts for the many genetic variations
observed in plants, animals, & other organisms
Summary of Mendel’s Principles
Inheritance of biological characteristics is
determined by individual units called genes.
Genes are passed from parents to their offspring.
2. If there are 2 or more alleles of a gene for a single
trait, some forms may be dominant & others
recessive
3. In most sexually reproducing organisms, each
individual has 2 copies of a single gene (1 from
each parent) & they separate when gametes are
formed
4. Alleles for different genes usually separate
independently of one another.
1.
Incomplete Dominance
 Cases where neither allele is dominant the
heterozygous individual will have a phenotype that is
a blend of the 2 alleles.
Codominance
 Both alleles for a gene are expressed in the
phenotype of a hybrid individual
Multiple Alleles
 genes that have >2 alleles
Polygenic Traits
 Traits controlled by the interactions of several genes
Genetics & the Environment
 Genes provide a plan for development but
how that plan unfolds also depends on the
environment
Name that type of inheritance
Name that type of inheritance!