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Celebrity Babies

When you look at the picture of a celebrity you see their phenotypes – or observable traits. For every characteristic (like eye color) there are different forms or varieties of that characteristic that someone could actually have (blue, green, hazel or brown eyes).

All of these traits are caused by variations in genes. Every gene comes in one of two different forms. We represent those forms by a letter, either as a capital letter or a lower case letter. For example, eye color has a gene that can come in the B form (brown) or the b form (non-brown). These different forms are called alleles.

Every individual has 2 copies of each gene, one from mom, the other from dad. Thus, for eye color, you could be:
BB – two brown alleles
Bb – one brown allele, one non-brown allele
bb – two non-brown alleles
These double letter pairs representing trait forms are called genotypes.

One allele is dominant. The other allele is recessive. The dominant allele masks or covers up the other gene. Brown eyes are dominant over blue eyes. If you have a brown allele, your eyes will be brown no matter whether the other allele is. Thus, if a person is Bb with one brown allele and one non-brown allele, then they will have brown eyes, not a mixture of brown and blue.

If you are BB, your eyes will be brown.
If you are Bb, your eyes will be brown.
If you are bb, your eyes will be blue.

Every gene has two alleles or forms, one that is dominant and one that is recessive. For each of the traits we looked at, there is a dominant and a recessive form. CelebTable1.gif
Hair texture is a little more complicated because curly textured hair (T) is not completely dominant over straight hair (t).
If you have one curly allele and one straight allele (Tt) then you end up with wavy hair. This is called incomplete dominance.

Step 1 – Figure out the genotype
So… what’s a genotype? Remember, everyone has two copies of every gene! One gene comes from each parent.

If a phenotype (an observable traits like eye color) is recessive (b), then the genotype (which forms of the gene are present) has to be two recessive alleles (bb).

If the phenotype is dominant (B), then the genotype could be EITHER two dominant alleles (BB) or one dominant and one recessive allele (Bb). In this exercise, if the dominant phenotype is present, assume that the individual has one dominant and one recessive allele (Bb) unless you know for SURE that NO relative (grandparent, aunt, uncle, parent or sibling) has the recessive trait. Only if NO relative is recessive should two dominant alleles (BB) be given. Determine the phenotype and genotype of each celebrity. Record the phenotypes and genotypes in a table. Make a table for each person like the one below without the 2nd and 3rd column.
(Make tables like the ones at this link or print them. )

Step 2 – Make eggs and sperm (Meiosis)
To begin, two gametes (sperm and/or eggs) will need to be made. Sperm and eggs are special because while every other cell in our bodies has two copies of our genes (one from mom and one from dad), sperm and eggs have only one copy of each gene.

Sperm and eggs are created through a process called meiosis. Meiosis is a special form of cell division in which you start with a parent cell with 2 copies of every gene and end up with a daughter cell that has only one copy of every gene. The two alleles for any given gene are randomly divided into gametes. Thus, if a genotype is Bb, some gametes will have the dominant B allele and some gametes will have the recessive b allele.

In this lab, you will flip a coin for each trait to determine which allele is in each gamete.

With your partner, decide which person will make sperm and which person will make eggs. Each person will make 2 gametes.

Look closely at your genotype. Toss the coin for each gene (each trait).
Heads  the gamete will have the first allele
Tails  the gamete will have the second allele

For example, let’s say your genotype is Bb for eye color. If you flip heads, then give sperm #1 the B allele. Flip again for the second gamete. If you flip tails, then give sperm #2 the b allele.

Fill in the sperm and eggs below for the celebrities you chose.

Notice, there is an extra line for gender under the sperm. That is because sperm pass on the information that determines whether the child will be a boy or a girl. The sperm providing partner should flip their coin one extra time.
Head  girl
Tails  boy

Step 3 – Fertilization

Offspring are now ready to be made! Two children will be made. Sperm #1 will fertilize egg #1 to create baby #1. They combine their genes to make a baby. That baby now has two copies of each gene – one copy from mom, and one from dad.

In the chart below, fill in each baby’s genotype and phenotype. Once you are finished with the final questions, feel free to draw a picture of what each child will look like as a freshman.

Conclusion Questions

1. a) How many copies of each gene do you have? _
b) Where do they come from?
2. What’s the difference between your phenotype and your genotype?
3. What does it mean for an allele to be dominant?
4. a) For the freckles trait, having freckles (F) is dominant while no freckles (f) is recessive.
b) What will someone that is Ff look like? _
5. a) If someone does not have freckles, what do you know about their genotype?
b) Explain how you know.
6. What are gametes?
7. How many copies of each gene do gametes have? _
8. a) Look at the gametes you made. Are they exactly the same? _
b) Explain why or why not.
9. a) Did either of the celebrity children look exactly like one parent?
b) How likely is it for someone to have kids that look exactly like them?
c) Explain why.