Download Punnett Squares - 7sciencewithmcmillan

Review Questions
________________ is the scientific
study of heredity.
A) Traits
B) Alleles
C) Genetics
D) Geneology
Review Questions
A behavioral or physical
characteristic is a ___________.
A) Trait
B) Gene
C) Allele
D) Chromosome
Review Questions
Which of the following genotypes is
homozygous dominant?
A) AB
B) aa
C) Aa
D) AA
Review Questions
Which of the following genotypes is
heterozygous?
A) AA
B) aa
C) Aa
D) AB
Review Questions
Every gene has ____ alleles?
A) one
B) two
C) three
D) four
Review Questions
Who is the “Father of Genetics”?
A) Isaac Newton
B) Robert Hooke
C) Gregor Mendel
D) Henry Lackes
Review Questions
Which of the following is NOT a
phenotype?
A) eye color
B) height
C) genes
D) attached earlobes
Review Questions
Write down the recessive allele in
the genotype Rr.
r
(recessive alleles are always lower-case!)
Dominant & Recessive Practice
T – straight hair
t - curly hair
 TT - Represent offspring with ______ hair
Straight hair
Dominant & Recessive Practice
T – straight hair
t - curly hair
tt - Represents offspring with ______ hair
Curly hair
Dominant & Recessive Practice
T – straight hair
t - curly hair
Tt - Represent offspring with _____ hair
Straight hair
Punnett Squares Notes
Punnett Squares
 Punnett Square – Diagram showing the
gene combinations that might result from a
genetic cross
 Used to calculate the
probability of inheriting
a particular trait
 Probability – The chance
that a given event will
occur
Punnett Square
Parent
Parent
Offspring
How to Complete a Punnett Square
Yy x Yy
When 2 heterozygous genotypes are
crossed, a parent can give contribute
either a recessive or a dominant allele
to the offspring.
Y-Yellow
y-white
Genotype:
1:2:1
(YY:Yy:yy)
Phenotype:
¾ (75%) Yellow
¼ (25%) White
How to Make a Punnett Square!
Give the genotype and phenotype for the following
cross: TT x tt (T = Tall and t = Short)
TT x tt
Step One: Set Up Punnett Square (put one parent on the
top and the other along the side)
TT x tt
Step Two: Complete the Punnett Square by crossing each male
and female gamete (to form a possible zygote).
TT x tt
Step Three: Calculate the genotype and phenotype
(remember that each box is 25%)
Genotype:
4 - Tt
Phenotype:
100% Tall
You Try It Now!
Give the genotype and phenotype for the following cross:
Tt x tt
Genotype:
Tt = 50%
tt = 50%
Phenotype:
50% Tall
50% Short:
Some Terminology
 P1 – Original parents
 F1 – First generation
 F2 – Second generation
 P1 X P1 = F1
 F1 X F1 = F2
Incomplete Dominance
Incomplete Dominance - Situation in which
one allele is not completely dominant over
another.
Example – Red and
white flowers are
crossed and pink
flowers are produced.
Codominance
Codominance - Situation in which both alleles
of a gene contribute to the phenotype of the
organism.
Example – A solid white cow is crossed with a solid
brown cow and the resulting offspring are spotted
brown and white (called roan).

+
Multiple Alleles
Multiple Alleles- Three or more alleles of
the same gene.
 Even though three or more alleles exist for a
particular trait, an individual can only have
two alleles - one from the mother and one
from the father.
Examples of Multiple Alleles
1. Coat color in rabbits is determined by a
single gene that has at least four different
alleles. Different combinations of alleles
result in the four colors you see here.
Examples of Multiple Alleles
2. Blood Type – 3 alleles
exist (IA, IB, and i),
which results in four
different possible blood
types
3. Hair Color – Too many
alleles exist to count

There are over 20
different shades of
hair color.
Multiple Alleles
 There Are Always Multiple Alleles!
 Genetic inheritance is often presented with
straightforward examples involving only two alleles
with clear-cut dominance. This makes inheritance
patterns easy to see.
 But very few traits actually only have two alleles with
clear-cut dominance. As we learn more about
genetics, we have found that there are often
hundreds of alleles for any particular gene.

We probably know this already - as we look around at
other people, we see infinite variation.
Polygenic Trait
 Polygenic Trait - Trait
controlled by two or more
genes.
 Polygenic traits often show a
wide range of phenotypes.
 Example: The wide range of
skin color in humans comes
about partly because more
than four different genes
probably control this trait.