Download BB or bb.

What’s a Punnett
Square?
Predicting Genetic Outcomes
• _Heredity_ :
the passing of traits from
parent to offspring
Traits are controlled by genes,
SO what is GENETICS?
__Genetics_: The study of how
traits are __inherited__.
GREGOR MENDEL
o First known _geneticist_
and “father of genetics”
o Was an Austrian monk, born
in 1822
o Did most of his genetic
studies on _pea_ plants
o He performed _cross_ - _pollination_
o He became the pollinator himself
o He controlled which plants mixed.
o Some traits Mendel worked with were
_shape__ of pea and it’s pod, _color__ and
shape of seeds, plant __height__, flower
position and flower color.
WHAT ARE ALLELES?
o Are ONE __form___ of a gene (there can
be more than one form)
o Sex cells have 1_ form of a gene on their
chromosomes
o Body cells have _2__ forms or ALLELES
for a single gene (you got one from Mom
and one from Dad)
o One may be __dominant___ over another. If this
happens, the dominant gene is the one expressed.
If not, the recessive trait is expressed.
DOMINANT AND RECESSIVE
o A __dominant__ allele:
will always be expressed and will “__mask__”
a recessive allele
o A __recessive___ allele
can only be expressed if there are no
___dominant___ alleles present.
Example:
Eye color—Brown color is dominant
and blue is recessive.
A person can have a brown allele and
a blue allele but will have brown eyes
because the brown allele is dominant
and “hides” the blue allele.
• Generally, dominant alleles are
represented with a __________
letter, and recessive alleles are
represented with a ___________
letter.
Example:
R= dominant r = recessive
Each
individual is
represented
by _2__
letters, one
for each
allele.
o “Purebred” individuals have two alleles of
the same trait
o Represented by two of the same letters. This
is called __homozygous_____.
For instance: BB or bb.
o Individuals with two different alleles or
two different forms of the gene would be
“hybrid”
o Represented by two different “letters” and is
called “__heterozygous____”. For instance: Bb
o The alleles present in the individual are
referred to as its ___genotype___. For
instance, BB, Bb, or bb.
o The PHYSICAL trait that shows,
regardless of genotype is called a
___phenotype___.
o For instance, Blue or Brown Eyes.
o Calculating Eye Color
PROBABILITY
o Helps predict the chance that
something will happen
o Example: the probability of throwing
heads or tails on a coin is _50_%
(1/2)
o Your predictions become more
accurate with the more trials you run!
Using a Punnett Square…
o Used to help predict Mendelian
genetics
Steps for using the Punnett square:
1) One parent’s alleles (_genotype___)
go along the top
2) The other parent’s __alleles___ go
down the side.
3) You fill in the squares like doing the
communicative property of
B
b
multiplication.
B
BB
Bb
b
Bb
bb
Steps for using the Punnett square:
Let’s say the parents are Bb and Bb
(the same genotype).
What would be their phenotype?
___Brown eyes_____
So you would predict:
1/4_offspring to be BB, or Brown Eyes
_2/4__ or _1/2_to be Bb, or Brown Eyes
and 1/4_ to be bb or Blue eyes
B
b
B
BB
Bb
b
Bb
bb
Practice Problem #1
• Predict the fur color of the offspring
of a brown heterozygous hamster and a
white homozygous hamster. Brown is
dominant. White is recessive.
• Use any letter you like.
Practice Problem #1
B
b
b
Bb
Bb
b
bb
bb
Practice Problem #2
• Predict the offspring of 2 white
homozygous cows. Black is dominant
over white.
• Use any letter you like.
Practice Problem #2
b
b
b
b
bb
bb
bb
bb
Practice Problem #3
• Predict the offspring of 2 Grey
Heterozygous rats. Grey is dominant
over white, which is recessive.
• Use any letter you like.
Practice Problem #3
G
G
g
GG
Gg
g
Gg
gg
Practice Problem #4
• Predict the pea shape of the
offspring of one Heterozygous round
Pea plant and one homozygous
wrinkled pea plant. Round is dominant
over wrinkled.
• Use any letter you like.
Practice Problem #4
R
r
r
Rr
Rr
r
rr
rr
Practice Problem #5
you don’t have to write this one down…
• What are the chances of having a boy
or a girl?
• How would you solve this one?
Practice Problem #5
X
X
X
XX
XX
Y
XY
XY