Transcript How to set up Punnet Squares

How to set up Punnet Squares
Punnet Square Vocabulary
 Genotype - An organisms
genetic makeup or allele
combination; for one
specific trait we use two
letters to represent the
genotype. A capital letter
represents the dominant
form of a gene (allele),
and a lowercase letter is
the abbreviation for the
recessive form of the
gene (allele).
 Ex. RR, Rr, rr
Punnet Square Vocabulary
 Phenotype - An
organisms appearance
or visible traits.
 Ex. Color, shape
Punnet Square Vocabulary
 Homozygous - Both
Genes (alleles) are the
SAME as each other
Ex. RR, rr
Punnet Square Vocabulary
 Heterozygous - Both
Genes (alleles) are
DIFFERENT from
each other
 Ex. Rr
Punnet Square Vocabulary
 Homozygous
DOMINANT - Both
Genes (alleles) are
DOMINANT (Capitol
letters) AND ARE THE
SAME AS EACH
OTHER
 Ex. CC
Punnet Square Vocabulary
 Homozygous
RECESSIVE - Both
Genes (alleles) are
RECESSIVE (lower
case letters) AND ARE
THE SAME AS EACH
OTHER
 Ex. cc
Punnet Square Vocabulary
 Heterozygous - Both
Genes (alleles) are
DIFFERENT from
each other
 Ex. Cc (one Capitol
letter one and lower
case letter)
Problem
Cross a short person
with one that is
heterozygous for
tallness?
Examining the problem…
 Here, you have to use your understanding of
the vocabulary to figure out what letters to use
in the genotypes of the parents. Where "T" =
tall Dominant, & "t" = short recessive. One
parent is Heterozygous which always means
one of each letter, so we'd use "Tt" The only
way for a person to be short is when it has 2
lowercase "t's", so that parent is “tt".
1. determine the genotypes of the
parent organisms
 Parent # 1
– Short person
 Homozygous Recessive
tt
 Parent # 2
– Tall person
 Heterozygous
Tt
2. write down your "cross"
(mating)
So the cross ends-up written like this…
Tt x tt
3. draw a p-square
4. "split" the letters of the genotype for each
parent & put them "outside" the p-square
 Take the
genotype letters
of one parent,
split them and
put them on the
left, outside the
rows of the psquare.
4. "split" the letters of the genotype for each
parent & put them "outside" the p-square
 Now take the two
letters of the
second parent's
genotype, split
them up, and
place them
above each of
the two columns
of the p-square.
5. determine the possible genotypes of
the offspring by filling in the p-square
 I kind of gave this away
already, but to
"determine the
genotypes of the
offspring" all we have to
do is fill-in the boxes of
the p-square. Again we
do this be taking a letter
from the left & matching
it with a letter from the
top. Like so:
Fill in the rest of the boxes…
Fill in the rest of the boxes…
Fill in the rest of the boxes…
6. summarize results (genotypes
& phenotypes of offspring)
Parents
("P" Generation)
Genotypes
Tt x tt
Offspring
("F1" Generation)
Phenotypes Genotypes
Tall x short
Phenotypes:
50% (2/4) Tt 50% tall
50% (2/4) tt 50% short
Punnet Square Steps
 1. determine the genotypes of the parent
organisms
2. write down your "cross" (mating)
3. draw a p-square
4. "split" the letters of the genotype for
each parent & put them "outside" the psquare
5. determine the possible genotypes of
the offspring by filling in the p-square
6. summarize results (genotypes &
phenotypes of offspring)