Punnett Square Notes
1.
For this assignment, you are to use this PowerPoint which contains
additional videos and the packet you picked up today.
2.
When you complete the entire packet, please show Mrs. Akona for credit.
Failure to do so will result in zero credit.
3.
After you show Mrs. Akona the completed packet, you can keep the packet
and use as notes to complete review worksheets that you will get over the
next couple days.
4.
I strongly encourage you to ask questions when you don’t understand. Mrs.
Akona is familiar with punnett squares. In addition to using her as a
resource, Mrs. Bellah next door has also opened her door to you for
additional help while I am away. Mr. Castro and Mr. Morales work at the
Waverider Learning Center after school who can also help you with
Punnett Squares. Please seek out these resources! They are awesome
people who are more than willing to help you clear up any confusion.
5.
Remember! All I ask is that you try. You will never learn unless you try!
Review on DNA & Intro to Genetics
click on this link if video pauses or runs slow
What are Punnett Squares
How to draw a punnett square
Notes: ALL 2010
What is Punnett Square?  
8.
Biologist use a diagram called a punnett square to help predict the
probability that certain traits will be inherited by offspring.
9. The punnett square used for crossing one trait (what is the prefix
for one) between two parents is called a monohybrid.
10. The punnett square used for crossing two traits (what is the prefix
for two) between two parents is called a dihybrid.
11. What are autosomes? The chromosomes pairs 1-22.
12. Traits inherited on chromosome pairs 1-22 are called autosomal
traits.
13.What is the 23rd pair of chromosomes called? The
sex chromosomes. Sex chromosomes determine
gender but they also contain genes for other traits
as well. For example, the gene for colorblindness is
located on the X chromosome.
14.Traits that are inherited on chromosomes pair 23,
the sex chromosomes are called sex-linked.
a. If the trait is on the “X” chromosomes it is called Xlinked.
b. If the trait is on the “Y” chromosome it is called Y-linked.
c. True or false? One females can inherit X-link traits while
only males can inherit Y-linked traits?
a.
FALSE! Both males (XY) and females (XX) can inherit X-linked
traits because the both carry the X-chromosome. However!
Males can only inherit Y-linked traits because they carry a Ychromosome. Females cannot inherit Y-linked traits because
they do not have the Y-chromosome.
15.Having the phenotype “freckles” is inherited
autosomal dominant. This means that the
gene for the trait freckles is found on one of
the chromosome pairs 1-22. In order to “get”
freckles you only have to inherit 1 copy of the
freckle gene.
Step 1 and 2
Step 5
F
f
f
Ff
ff
f
Ff
ff
a. When we talk about phenotype, we are talking about
what is see or “features”
b. So write all the possible phenotypes that could result by
crossing the genotypes of these two parents. Freckles and
no freckles.
c. Now… write the above phenotypes in a ratio form. 2
freckles : 2 no freckles
d. When we talk about genotype, we are talking about the
letters used to represent the genes for traits.
e. Now…write all the possible genotypes that could result by
crossing the genotypes of these two parents. Ff and ff
f. Now…write the above genotypes in a ratio form. 2Ff : 2ff
17.
Ff
Ff
F
f
F
FF
Ff
f
Ff
ff
a) Write all the possible phenotypes that could result by
crossing the genotypes of these two parents. Freckles
and no freckles
b) Now…write the above phenotypes in a ratio form.
3freckles : 1 no freckles
c) Write all the possible genotypes that could result by
crossing the genotypes of these two parents. FF, Ff, ff
d) Now…write the above genotypes in a ratio form. 1FF :
2Ff : 1ff
e) What is the probability of producing an offspring that
is homozygous dominant for freckles (hint: write first
as a fraction, then as a percent)? 25%
f) What is the probability of producing an offspring that
has no freckles? 25%
g) What is the probability of producing an offspring that
is heterozygous for freckles? 50%
19. Problem: Let “c” represent a cleft chin.
Cross a parent that is homozygous no cleft
chin with a parent that has a cleft chin.
a) What is the phenotypic ratio? 4 no cleft chin
b) What is the genotypic ratio? 4Cc
c) What is the probability of producing an
offspring that has no cleft? 100%
d) What is the probability of producing an
offspring that has a cleft chin? 0%
• Complete 20-22 on your own.
23. Some genetic diseases are inherited autosomal
recessive. This means in order to be affected
with specific genetic diseases, the offspring needs
to inherit two “diseased” allele (one from each
parent) to be affected.
24. Congenital neutropenia, severe (SCN) is a
genetic disease that is inherited autosomal
recessive. In this disease, children with this
condition lack neutrophils (a type of white blood
cell that is important in fighting infection). These
children suffer frequent infections from bacteria
which in the past led to death in three-quarters
of cases before 3 years of age. This disease is also
known as severe congenital neutropenia (SCN).
Let “d” represent the disease. Cross 2 parents
who are carriers of this disease.
#24. continued
• Phenotypic ratio? 3unaffected: 1affected
• Genotypic ratio? 1DD: 2Dd: 1dd
• Probability of producing an unaffected
offspring? 75%
• Probability of producing an affected offspring?
25%
• Probability of producing a carrier of the
disease? 50%
25. Phenylketonuria (PKU) is an inherited error of metabolism
caused by a deficiency in the enzyme phenylalanine
hydroxylase. This is a metabolic disorder that leads to a
harmful buildup of the phenylalanine in the body. Normally
the “working” enzyme coverts phenylalanine into tyrosine.
The severity of the symptoms can range from severe
enough to cause mental retardation to mild enough not to
require treatment. Severity is determined by the level of
impairment of enzyme activity of phenylalanine
hydroxylase. PKU is inherited autosomal recessive.
Let “P” represent unaffected while “p” represent affected.
Cross an affected father with a mother that is a carrier.
#25. continued
• Phenotypic ratio? 2 unaffected : 2 affected
• Genotypic ratio? 2Pp : 2pp
• Probability of producing an unaffected
offspring? 50%
• Probability of producing an affected offspring?
50%
• Probability of producing a carrier of the
disease? 50%
• Complete the rest of the packet and correct
your answers with Mrs. Akona