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Human Genetic's






A worldwide effort is under way to develop and apply the technologies needed to completely map and sequence the human genome.

There are many ethical and moral issues that need to examined as we learn more about this area of study. Be sure to keep these issues in mind.



Learning how you are related to or linked to your origin



Passed down from your parents



Personal Characteristics, things about you—such as eye color, skin color, and blood type—that are specific to you



One of a kind

Description:  The value of studying genetics is in understanding how we can predict the likelihood of inheriting particular traits.  This can help plant and animal breeders in developing varieties that have more desirable qualities.  It can also help people explain and predict patterns of inheritance in family lines. (This may explain why you look so much like another relative)



History of Genetics:

A monk named Gregor Mendel discouraged individual traits are determined by discrete factors called genes.Follow the animated lessons below  on how Gregor Mendel worked with pea plants to determine "traits.

 The page will look like this:




Now play the Interactive and practice crossing the peas.










One of the easiest ways to calculate the mathematical probability of inheriting a specific trait was invented by an early 20th century English geneticist named Reginald Punnett . His technique employs what we now call a Punnett square.  This is a simple graphical way of discovering all of the potential combinations of genotypes that can occur in children, given the genotypes of their parents.  It also shows us the odds of each of the offspring genotypes occurring.

Setting up and using a Punnett square is quite simple once you understand how it works.  You begin by drawing a grid of perpendicular lines or using an excel spreadsheet selecting three rows across and three rows down.

basic Punnett square grid framework--essentially the beginning of tick-tack-toe game box

Next, you put the genotype of one parent across the top and that of the other parent down the left side.  For example, if parent pea plant genotypes were YY and GG respectively, the setup would be:

Punnett square with the genotype of one parent on the top with one letter in each square and the genotype of the other parent on the left side with one letter in each square                                        

Note that only one letter goes in each box for the parents.   It does not matter which parent is on the side or the top of the Punnett square.  

Next, all you have to do is fill in the boxes by copying the row and column-head letters across or down into the empty squares.  This gives us the predicted frequency of all of the potential genotypes among the offspring each time reproduction occurs.

same as the previous Punnett square but with the expected genotype frequencies of offspring are indicated in the 4 empty squares on the lower right

In this example, 100% of the offspring will likely be heterozygous (YG).  Since the Y (yellow) allele is dominant over the G (green) allele for pea plants, 100% of the YG offspring will have a yellow phenotype, as Mendel observed in his breeding experiments.

In another example (shown below), if the parent plants both have heterozygous (YG) genotypes, there will be 25% YY, 50% YG, and 25% GG offspring on average.  These percentages are determined based on the fact that each of the 4 offspring boxes in a Punnett square is 25% (1 out of 4).  As to phenotypes, 75% will be Y and only 25% will be G.  These will be the odds every time a new offspring is conceived by parents with YG genotypes. 



Punnett square with both parents heterozygous (YG) showing that the offspring probablities are 25% YY, 50% YG, and 25% GG




Check out this animation of how it works





An offspring's genotype is the result of the combination of genes in the sex cells or gametes (sperm and ova) that came together in its conception.  One sex cell came from each parent.  Sex cells normally only have one copy of the gene for each trait (e.g., one copy of the Y or G form of the gene in the example above).  Each of the two Punnett square boxes in which the parent genes for a trait are placed (across the top or on the left side) actually represents one of the two possible genotypes for a parent sex cell.  Which of the two parental copies of a gene is inherited depends on which sex cell is inherited--it is a matter of chance.  By placing each of the two copies in its own box has the effect of giving it a 50% chance of being inherited.

If you are not yet clear about how to make a Punnett Square and interpret its result, take the time to try to figure it out before going on.




 Try the simulation below to see how it works with mice


Teaching with Gizmos

icon Genetics and Mouse Breeding (5:57 minutes)







Genetics in the News
April 04, 2008
DNA Differences Make Smoking More Dangerous



Ethics & Issues Survey
Ethics & Issues Survey What do you think?
Take this survey to explore and share your views on three current issues about genetics and human health.

At the Museum
At the Museum Genetics: Technology With a Twist
Visit Today! Explore the forefront of emerging genetic technologies.


What traits do you share with your parents?


genetic traits worksheet.doc

Online Exhibits
Zooming into DNA Zooming into DNA
View amazing real images of cells, chromosomes and DNA from 100X to 900,000X.
What Color Eyes Will Your Children Have? What Color Eyes Will Your Children Have?
Learn about genetic inheritance while having fun with our interactive eye calculator.
Know Your FoodsKnow Your Foods
spacerAre you eating genetically modified foods?
Insider's View

Insider's View
A look at genetic research at the Stanford Human Genome Center.

Why is it important for you to know about Punnett squares?  The answer is that they can be used as predictive tools to see what possibilities of diseases a child might have the possibility of getting.  Let us assume, for instance, that both the women  and the man are carriers for a particularly unpleasant genetically inherited disease such as cystic fibrosis.  What is the possibility of their child getting the disease even when neither parent got the disease but were carriers for it?


Punnett square with both parents heterozygous (Aa)     If both parents are carriers of the recessive
allele for a disorder, all of their children will
face the following odds of inheriting it:
25% chance of having the recessive disorder
50% chance of being a healthy carrier
25% chance of being healthy and not have
        the recessive allele at all
Are Punnett Squares Just Academic Games?

If a carrier (Aa) for such a recessive disease mates with someone who has it (aa), the likelihood of their children also inheriting the condition is far greater (as shown below).  On average, half of the children will be heterozygous (Aa) and, therefore, carriers.  The remaining half will inherit 2 recessive alleles (aa) and develop the disease.

Punnett square with heterozygous (Aa) and homozygous recessive parents (aa)     If one parent is a carrier and the other has a
recessive disorder, their children will have the
following odds of inheriting it:
50% chance of being a healthy carrier
50% chance having the recessive disorder

After reviewing the information in your text book

Please pick 2-3 of these sites to broaden your understanding of genetics


Understanding genetics-online virtual









Genetics in Crime Solving


That DNA is unique from person to person but the same from cell to cell in one person can be a handy thing, especially when it comes to DNA fingerprinting. DNA fingerprints can be used for anything from determining a biological mother or father to identifying the suspect of a crime. And, as may someday prove to be the case with Sam Sheppard, it can be used to clear someone's name.


DNA fingerprint But what exactly is a DNA fingerprint? Well, it certainly isn't an inky impression of a DNA strand. Compared to unimaginably small DNA, a fingerprint is HUGE. So what is it that we're looking at, and how is one of these fingerprints made?


Here's your chance to find out. You'll find out by solving a mystery -- a crime of sorts. Solving the mystery involves creating a DNA fingerprint (we'll supply the lab and all necessary materials) and comparing this fingerprint to those of the suspects.


Are you ready? Then get to work!







Interactive labs

 Genetic DNA



Class Project


You will be given two coins. Flipping the coins will determine which disease your offspring will have based on where you placed it on the Chromosome.

Next Research the following diseases




National Institutes of Health maintains a user-friendly website giving an

overview of deafness and hereditary hearing loss.


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