Using the model of a Punnett Square to predict offspring ratios

Objectives Objective 1: Students will know that chromosomes have genes that control the phenotype (appearance) of organisms Objective 2: Students will calculate the percentages of various types of potential offspring based on a simple dominance model and using a single trait. Objective 3. Students will extend the model of the Punnett Square in order to apply the concept of simple dominance to new traits.

“Will your kids be able to roll their tongues?”

Sperm + Egg = Offspring We have been talking about the idea of sperm and egg getting together to create a new life. We know that this happens in both plants and animals. In animals, the male contributes the sperm, and the female contributes the egg. In plants, the male part of the plant contributes pollen, which acts like the sperm, and in the female part of the plant is the egg.

Mysteries & Inheritance If we look at brothers or sisters who all come from the same parents, do these brothers and sisters all look exactly the same? So are we not clones of our parents? What are some differences between brothers or sisters who come from the same parents? There are some mysteries involved in how you all have inherited traits from your fathers and mothers. For those of you who are adopted think about a friend’s family or help me understand my family.

More questions If you have a mother who is 5 feet 5 inches tall and a father who is 6 feet tall, and they have four children, how tall do you think they should be? All the same? Is it possible for a child to end up shorter than both parents? Or taller than both parents?

And what about… Have any of you seen a person who looks like they have the traits of one of their grandparents but not the parent, like the traits skipped a generation? Do any of you have traits more similar to your grandmothers or grandfathers than your parents?

To begin to understand how these kinds of traits can be inherited, we have to go back to the idea of the sperm and the egg contributing to who we are. We have mentioned that in order to create a human being, you need sperm from a father & an egg from the mother. These sex cells carry chromosomes. Is this an accurate picture?

23+23 46 Chromosomes Female & Male

that make up the human body. These paired chromosomes are made up of thousands of sections called genes. Each gene controls some kind of trait, like color of hair, or color of eyes, or contribute to height. There are about 100,000 genes that make up the human body. 1 eye color gene from mom and one from dad. Mother Father

Which form of the gene is dominant? Recessive? What is interesting is that we can tell a little about what kind of genes we have by observing various traits in ourselves. Free (F) Attached (f) What is interesting is that we can tell a little about what kind of genes we have by observing various traits in ourselves. I’d like you to take a little data now with your classmates (show earlobes and tongue OH and talk about which is dominant). There is a gene for whether or not your earlobes are attached and a gene for whether you can roll your tongue. I’d like half of you in pairs, to record the number of people that have attached versus free earlobes. The other half will do another chart for the tongue. For those of you with free earlobes- what does this mean about your parents? What if a kid gets 1 gene for free earlobes from 1 parent and a gene for attached earlobes from the other parent? What’s the kid going to look like? What are our options- free, attached, both. WHY will the kid end up with free earlobes???? ONE GENE WINS OUT- like many genes, some forms of the genes are dominant and some are recessive. We use upper case letters to represent dominance and lower case letters to represent recessiveness. Roll (R) Not Roll (r) Which form of the gene is dominant? Recessive?

? Beaker Babies F F or f f F f Quick exercise to look at what the possibilities are for a child with a mom who has attached and a father who has free earlobes. What MUST the mother have for her genes? ff What CAN the father have for his genes? FF/Ff NOW- partner up and figure out 1st what genes you have and 2nd what genes an offspring would have from the 2 of you. ?

f F F F F f f F f f F f Punnett Square Male Punnett Square f F F F F f f F f f F ema l e F f 1905, Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including sex linkage and sex determination. He worked with the feather color traits of chickens in order to quickly separate male and female chickens. These are the combinations that are possible. Only possible! They are all equally possible. Go through each cell, what will they look like? What fraction will have free earlobes? Percent? NOW- you and your partner do a punnett square for you. Isn’t this easier for predicting what kids will look like??? NOW- try one for tongue rolling… Phenotype Ratio (what shows): 3:1

Now to answer our question for the day… Male r r r F ema l e rr r NOW- you do one for you and your partner. Phenotype Ratio (what shows): 4:0

Tasks for the day: 1. If you can roll your tongue, what do you know about the two genes that you have inherited? Explain. 2. If you cannot roll your tongue, what do you know about the two genes you have inherited? Explain. 3. Using a Punnett Square, can you show if it is possible to have another and a father who can roll their tongues, but have children that cannot roll their tongues? Explain. 4. Using a Punnett Square, can you show if it is possible to have a mother and a father who cannot roll their tongues, but have children that can roll their tongues? Explain. 5. Extra challenge: Create a Punnett Square that incorporates not one, but two traits (tongue rolling AND earlobes). Hint: You will need a total of 16 cells in your Punnett Square. Tell about the different kind of offspring that are possible.

So what did we learn today? About ourselves About genes About inheritance About Punnett Squares About science

Where are we going? To study the particular diseases that can be inherited & what those patterns of inheritance are… We can laugh about rolling our tongues but some genes control some pretty serious traits- for example genes that control genetic disorders such as sickle cell anemia.

How did your partner help you learn today? What’s something you did well together? Say thanks & something you appreciate about them.

Female- Body Cell Chromosomes

Male- Body Cell Chromosomes