Download Learning Goal B

Learning Goal 1
The Work of Gregor Mendel
Background on Gregor Mendel
Details Reasons for Choosing Peas Mendel’s Experimental Design
His Pea Experiment Mendel’s Results Mendel’s Laws
Law of Dominance Law of Segregation Law of Independent Assortment Genetic Terms
Alleles Homozygous Heterozygous Genotype Phenotype -
Unit IV
Learning Goal 1
Describe the research of Gregor
Mendel and predict the outcome of
genetic crosses.
Background on Gregor Mendel
• Details
• Austrian monk with an
interest in gardening
and a good
knowledge of
mathematics.
• In the 1840’s he
experimented with the
traits of garden peas
(Pisum sativum).
Reasons for Choosing the
Garden Pea
• Many varieties exist.
• Easy to observe
contrasting traits.
• They self-pollinate.
• They reproduce
quickly.
Mendel’s Experimental
Design
• His Pea Experiment
• He allowed each variety to
self-pollinate for several
generations to ensure that they
were true-breeding (offspring
always exhibited the same
trait). He called this the P1
(parent) Generation.
• He took two of these parent
plants with contrasting forms of
the same trait and crosspollinated them.
• The plants that resulted from
this cross were called the F1
Generation.
• Mendel then allowed the F1
plants to self-pollinate to
produce the F2 Generation.
Mendel’s Results
• For every trait, one form would
disappear from the F1
generation.
• The disappearing trait
reappeared in the ¼ of the F2
generation.
• This was true of all seven traits
that Mendel looked at.
• He used the term dominant to
refer to the form of the trait
exhibited in the F1 generation
and recessive to refer to the
disappearing trait.
Mendel’s Laws
• Law of Dominance –
One form of each trait is dominant and one is
recessive.
Law of Segregation
• Members of each
gene pair (alleles)
separate during
gamete formation
(meiosis).
Law of Independent Assortment
• The genes for
different traits
separate
independently from
one another during
gamete formation.
Genetic Terms
• Alleles – members of a gene pair symbolized by
letters. Dominant alleles are capital letters, and
recessive alleles are lower case.
• Homozygous – the alleles of a gene pair are
identical (RR or rr).
• Heterozygous – the alleles of a gene pair are
different (Rr).
• Genotype – describes the types of alleles of a
gene pair
• Phenotype – describes the expression of the
trait in the appearance.