1. Fair Use
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CopyrightLaw and is restricted from
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2. How to Complete a Punnett Square
Matthew F Poston
3. What is a Punnett Square?
The Punnett square method, named after R.C. Punnett is a convenient way to predict the genotypes and phenotypes of offspring. The Punnett square allows you to determine all the types of genetically different gametes that can be produced by the male and female parents.
4. Punnett Square
To the right you will notice a Punnett square that will help you determine the outcome of a single-trait cross.
5. So how does one complete a Punnett square?
First, you would need to find out which alleles are dominant and recessive. You can do this by looking at the chart provided in this mini-lesson.
Lets say we wanted to figure out if a gamete is going to have dimples. Dimples are dominant over no dimples. Lets assign the dominant allele (dimples) the capital letter D and the recessive allele (no dimples) the lowercase d.
6. Dominant and recessive trait chartCharacteristics in the left-hand column dominate overthose listed in the right-hand column
Dominant traits
browneyes
farsightedness
normal vision
normal vision
normal vision
dark hair
curly hair
widow's peak
dimples
unattached earlobes
broad lips
double-jointedness
short digits
immunity to poison ivy
normal pigmented skin
normal blood clotting
normal hearing
Recessive Traits
grey, green, hazel, blue eyes
normal vision
nearsightedness
night blindness
color blindness*
blonde, light, red hair
straight hair
normal hairline
no dimples
attached earlobes
thin lips
normal joints
normal digits
susceptibility to poison ivy
albinism
hemophilia*
congenital deafness
* sex-linked characteristic
7. Completing the Punnett square
Lets say we have a mother who is
homozygous recessive (dd) for the trait. dd
meaning not having dimples.
We also have the father who is
heterozygous (Dd) for the trait. Dd
meaning he has dimples but also carries the
recessive trait (d). The recessive trait could
possibly be the allele he passes to his
offspring.
8. Drawing and completing the Punnett square
D
d
d
d
d
d
D
d
d
d
D
d
When the narrator prompts you to click, please left click your mouse once or hit the key once.
9. Outcomes
Genotypes
The possible genotypes are
Dd and dd. There is a 50%
chance that the offspring
will have dimples and be a
carrier of the recessive trait
from the genotype Dd. There is
also a 50% chance that the
offspring will not have dimples and
carry both alleles for not having
dimples from the genotype dd.
Phenotypes
The offspring will have a
50% chance of displaying
the physical characteristic
of having dimples and 50%
ofdisplaying the physical
characteristic of no dimples.
10. Bibliography
Graphics
http://www.biologyjunction.com/genetic_traits_activity.htm
http://www.miracosta.edu/home/mspring/Project%20example.htm
Data
http://www.blinn.edu/socialscience/LDThomas/Feldman/Handouts/0203hand.htm
Narration
Shellie Marie Poston is in the 6th grade at Southeastern Middle School in Walnut Cove, NC.