Transcript Genetics Punnett Square

T
t
Tt
t
GENETICS
PUNNETT SQUARE
T
EXPECTATION
Make predictions about possible
outcomes of various genetic
combinations of inherited
characteristics.
PUNNETT SQUARE
RULES
A Punnett square is
a tool used to
predict the possible
genotypes for the
offspring of two
known parents.
PARENT’S GENES
PARENT’S GENES
VOCABULARY
Alleles
Different forms of a trait that R, r, T, t
a gene may have
Homozygous
An organism with two alleles
that are the same
RR, rr, TT, tt
Heterozygous
An organism with two
different alleles for a trait
Rr, Tt
Phenotype
The physical appearance of
an organism (what we look
like)
Tall, short, curly, straight
Genotype
The genes of an organism
RR, TT, Rr, Tt, rr, tt
Dominant
A trait that dominates or
covers up the other form of
the trait
Represented by an uppercase
letter
R or T
Recessive
A trait that is covered up by a Represented by a lowercase
dominant trait
letter
r or t
PUNNETT SQUARE
1. The parent’s alleles
go on the OUTSIDE
of the square.
RR X rr
r
r
R
R
HOW TO USE A PUNNETT
SQUARE
1. The parent’s alleles
go on the OUTSIDE of
the square.
NOTE: The
ORDER DOES
NOT matter in the
boxes, but
uppercase first is a
good rule.
R
R
r
Rr
Rr
r
Rr
Rr
2. DROP the
letters on the top
into each square.
3. MOVE
each letter on
the side into
each square.
HOW TO USE A PUNNETT
SQUARE
WHAT DO THE
RESULTS SHOW?
If B is the
DOMINANT
allele for BLACK
RESULTS:
B
B
PHENOTYPIC:
b
100% BLACK
Bb
Bb
And b is the
RECESSIVE allele
for BROWN
b
Then, we can make
predictions about
the outcomes.
4:0 RATIO, BLACK
TO BROWN
GENOTYPIC:
Bb
Bb
100% Bb
4:0 ALL Bb
HOW TO USE A PUNNETT
SQUARE
LET’S LOOK AT
WHAT ARE
THE RESULTS?
ANOTHER
PUNNETT SQUARE
AND PREDICT
THE OUTCOME.
T
t
PHENOTYPIC:
75% TALL
T is the
DOMINANT
allele for tallness.
t is the
RECESSIVE allele
for shortness.
T
TT
Tt
25% SHORT
3 : 1 RATIO:
TALL TO SHORT
t
Tt
tt
GENOTYPIC:
1TT: 2Tt: 1tt
1:2:1 RATIO
25 %TT, 50% Tt,
25% tt
PUNNETT SQUARE
PRACTICE
Complete Punnett Square:
a. Yellow is dominant (Y).
b. Green is recessive (y).
c. Father - yy
d. Mother - Yy
e. Identify the phenotype and
genotype.
PUNNETT SQUARES
Set up the square.
Complete PunnettSquare:
a. Yellow is dominant (Y).
b. Green is recessive (y).
c. Father - yy
d. Mother - Yy
e. Phenotype –
f. Genotype –
PUNNETT SQUARES
KEY
Complete Punnett Square:
a. Yellow is dominant (Y)
b. Green is recessive (y)
Y
y
y
Yy
yy
y
Yy
yy
c. Father - yy
d. Mother - Yy
e. Phenotype - 50% Yellow
and 50% green
f. Genotype - 50% Yy and 50% yy