Transcript Mendelian Inheritance

Mendelian Inheritance
Gregor Mendel
• Mendel was in a unique
position to discover
patterns of inheritance
• He was a monk who
had been raised as a
farmer and who studied
mathematics in Vienna
• Considered the “Father
of Genetics”
Blending Inheritance
• Blending Inheritance
Up to this time, it was generally thought
that resulting offspring were a blend of
the traits possessed by their parents
• Traits are inheritable characteristics
passed from one generation to the next
Mendel’s Pea Plants
• Mendel identified
and studied seven
different traits, each
of which had two
separate forms
called a Phenotype
• For example the trait
Plant Flower Color
had two forms:
Purple and White
Creating Purebred Plants
• Due the unique
petal arrangement in
pea plants, it is
common for them to
“self-pollinate’
• Self-pollination
results in offspring
that are identical
(clones) to their
parents
The Parental Cross
• Mendel first “CrossPollinated” opposing
purebred forms of a trait
(had to insure no SelfPollination)
• Example: Cross of
Purebred Purple and
White Flowers
• All of the offspring
produced Purple
Flowers
Parental Cross: Conclusions
• Mendel concluded that one form of a
trait is Dominant over the other form of
the trait, which is Recessive
• This demonstrated that Blending
Inheritance was not correct
The First Filial Cross
• Mendel CrossPollinated offspring
from his Parental Cross
and observed that both
forms of the trait appear
in the offspring
• The ratio of the
dominant to the
recessive phenotype
was 3:1
First Filial Cross: Conclusions
• Mendel concluded that the F1
individuals must be carrying the
recessive form of the trait even though it
remains hidden
Genotype Shorthands
• Allele is the genetic shorthand (single
letter) for the inheritable factors that we
now know are genes (example: P, p)
• Genotype is the genetic makeup of an
individual (example: PP, Pp, or pp)
Homozygous Dominant = PP
Heterozygous = Pp
Homozygous Recessive = pp
Producing Purebred Plants:
Punnett Square
P
P
P
PP
PP
P
PP
PP
The Parent Cross:
Punnett Square
p
p
P
Pp
Pp
P
Pp
Pp
The First Filial Cross:
Punnett Square
P
p
P
PP
Pp
p
Pp
pp
Two Trait Crosses:
Dihybrid Cross
TR
Tr
tR
tr
TR
TTRR TTRr TtRR TtRr
Tr
TTRr TTrr
TtRr
Ttrr
tR
TtRR TtRr
ttRR
ttRr
tr
TtRr
ttRr
ttrr
Ttrr
Non-Mendelian Forms of
Inheritance
•
•
•
•
Incomplete Dominance
Codominance
Multiple Alleles
Gene Linkage