Exceptions to Mendel`s Principles
Download
Report
Transcript Exceptions to Mendel`s Principles
Probability and Punnett
Squares
Copy what is in yellow
Probabililty
The
likelihood that a particular event
will occur.
Flip a coin…what is the probablity it will land on
heads? Does your probablility change depending on
how many times you flip the coin?
Principles
of probability can be used
to PREDICT the outcome of genetic
crosses.
But… Probability cannot predict the
exact or precise outcome of an event!
Punnett Square
Diagram
showing gene combinations that
might result from a genetic cross.
Law of Segregation: the separation of
alleles during gamete formation.
Monohybrid Cross: punnett square cross
looking at one trait.
Dihybrid Cross: Punnett square cross
looking at two traits
Ratios: Add up to 4!!
Phenotypic
ratio: physical appearance of
offspring
: # of recessive
# of dominant
Ex: 2 white flowers : 2 red flowers
Genotypic
ratio: combinations of letter
pairings
# homozygous : # heterozygous : # homozygous
dominant
recessive
Ex: 1 RR : 2 Rr : 1 rr
Law of Segregation
states
that allele pairs separate or
segregate during gamete formation, and
randomly unite at fertilization.
There are four main concepts related to
this principle.
A gene can exist in more than one form.
Organisms inherit two alleles for each trait.
When gametes are produced (by meiosis), allele pairs separate
leaving each cell with a single allele for each trait.
When the two alleles of a pair are different, one is dominant and
the other is recessive.
Punnett Square Practice #1
What
would be the outcome of crossing a
heterozygous tongue rolling parent with a
homozygous non tongue rolling parent?
The ability to roll your tongue is dominant.
Heterozygous
= Aa
Homozygous = aa
Punnett Square Practice #2
What
would be the outcome of crossing a
heterozygous long haired cat with a
homozygous long haired cat?
Long Hair is the Dominant Trait
Heterozygous
= Ll
Homozygous = LL
Punnett Square #3
What
would be the outcome of crossing a
homozygous dominant tongue roller with a
non tongue roller?
Homozygous
Non
Dominant ?
Tongue Roller (recessive) ?