Genetics, Punnett Squares, and probability.
Standards: *Note: I have many ELD standards as well, but am not including them on the website for lack of space.*
7.2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for under standing this concept:
b. Students know sexual reproduction produces offspring that inherit half their genes from each parent.
d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.
· Laboratory worksheet “Genetics with a Smile” (see Attached) – one for each student
· “Genetics with a Smile Directions” Sheet (see Attached) – one for each student
· “Smiley Face Traits” Sheet (see Attached) – one for each student
· Red Poker chips with “D” on one side and “r” on the other – one for each student
· Blue Poker chips with “D” and multiple “X”s on one side and “r” and multiple “Y”s on the other – one for each student
· One box of coloring supplies for each group of four students
Students will already have considerable practice with Punnett Squares and the following vocabulary terms and their meanings: dominant, recessive, genotype, phenotype, homozygous, heterozygous, purebred and hybrid. They must also be able to determine the probability of traits occurring. They will already be aware that the options for a trait’s probability are 0/4, ¼, 2/4, ¾, or 4/4; they will also know that these fractions can be expressed in percentages as 0%, 25%, 50%, 75% and 100%, respectively.
Part A - Choosing traits
1. Check to make sure all supplies are present.
2. Each member will need an orange characteristic paper to draw their baby.
3. Each member will need a red chip to represent mom’s DNA and a blue chip to represent dad’s DNA.
4. Flip the red chip (female) for the first trait (Face Shape).
5. Circle whether you flipped a dominant (C) or a recessive (c) under female in your data table.
6. Flip the blue chip (male) for the first trait (Face Shape).
7. Circle whether you flipped a dominant (C) or a recessive (c) under male in your data table.
8. Repeat directions 4-7 for all traits.
9. Use the orange characteristic paper to write all the genotypes and phenotypes based on what you flipped.
Part B - It's a boy! It's a girl!
10.Flip only the blue chip to determine the sex of your baby because male sperm cells carry the 2nd X chromosome for girl or the Y chromosome for boy.
11.If your baby is a girl, she must have a pink bow. If your baby is a boy, he must have a blue bow.
12. Draw your baby.
13. Answer the questions.
The purpose for this experiment is to solidify the concept of inheritance; specifically, the students will gain an understanding of how half of the traits come from the female parent and the other half from the male parent. By flipping the chip for each trait, students should realize that the chances of inheriting each allele 50% from each parent. They will also continuously write the new genotypes and phenotypes and gain practice in these tasks. The repetition ought to be enough to ingrain in them the concept of inheritance. The sketching is a fun way to put all of these concepts together (literally), and it gives the students an opportunity to be creative. It is also a way to synthesize a "baby" from the traits.
1. Why did you only need to flip the male parent chip in order to determine the gender of the baby?
If you looks on the traits page, you will see that the genotype for female gender is XX. If you were to put an X on one side of a chip and another X on the other and flipped the chip, you would ALWAYS get an X. Henceforth, you would not need to flip the female chip because you would get an X no matter what. The genotype for male gender is XY, however. You need to flip the male chip because the male determines the gender of the baby.
2. Uncle Smiley, who is heterozygous for a yellow face (Yy), married a woman with a green face. Create a Punnett square to show the possible face color genotypes for their children.
3. Aunt Smiley has the cutest pointed ears (vv) and would love to have children with pointed ears! What type of ears would her husband need to have in order to get her wish? Give the genotype and phenotype as part of your answer.
Her husband would need to either have pointed ears as well (vv) or be heterozygous for curved ears (Vv). If her husband had the heterozygous curved ears, however, her children would only have a 50% chance of having pointed ears. In order to guarantee pointed eared children, Aunt Smiley should marry a pointed eared man.
The first application to everyday life that this experiment addresses is inheritance of traits from parents to children. They are flipping the chips to show that to inherit a trait from a parent is both dependent upon genotype and chance. They will actually be able to look at their own parents’ traits and their own traits and perhaps understand why they look like a combination of their parents’ traits.
The second application comes in when the students determine their baby’s gender and when they answer the first question. It is intended to have students think about why the baby’s gender is not determined by the female parent. It also relates back to being homozygous or heterozygous for a trait; except, here we talk about a whole chromosome.
Finally, this experiment is applicable to everyday life because it will solidify that dominant traits are always expressed over recessive. They will be able to conjecture why some traits (on an animal, plant, or anything) are more numerous and expressed.
C. Waishwile, personal interview. April 4-8, 2011.