Project cost ($):
The student needs to perform coin tosses and draw a creature using a key.
You will need some pennies, paper and colored pencils - all of these are easily found at home.
Heredity can be a complicated process, but the basic principles of heredity result from the fact that you inherit half of your genes from your mother and half from your father. Because of this, heredity is comparable to a coin toss, with the genes of each parent represented by one side of the coin. For each trait that you have, you get heads or tails, your mother's or father's genes. In this project, you are going to travel to the planket Planktonia to perform breeding experiments. You will design a zoomonster by performing coin tosses for each trait. This project will give you a sense of the diversity of phenotypes that can result from two parents. Good luck and remember to wear your breathing mask!
To gain an understanding of the basic principles of heredity. To gain an understanding of the concept of probability and its role in heredity.
Have you ever looked around and marvelled at how different one person is from another in terms of physical appearances as well as behaviour? Some people are tall and others are short. Some people are talkative, while others are quiet.
Perhaps you and your sibling are nothing alike! Or perhaps you look a lot like one of your relatives? In that case you may wonder, what are the odds of you looking so much like your relative?
In fact, it isn't so strange to think about the odds of a person turning out the way they are. We are all a result of the combined influence of our genes and our environment - nature and nurture. Certain traits, however, are largely determined by our genes. The best example of this is whether we are male or female. We each have 23 pairs of chromosomes. Remember, a chromosome contains our DNA and our DNA determines our traits. If we are female our 23rd chromosome pair is XX, but if we are male our 23rd pair is XY.
When an ovum (human egg) is fertilized, half of its genetic material comes from the mother and half from the father. Every baby inherits an X from Mom, and either an X or a Y from Dad. The likelihood of having a particular outcome for an event is called probability. In this case, the event is the baby, or egg fertilization, and the outcome is its sex. Consider a coin toss. If there are two possible outcomes with every coin toss, what is the probability of flipping heads? Since the coin is not weighted on one side, flipping heads or tails are both equally likely outcomes. When the probabilities of two outcomes are equal, each is expressed as 1/2 (50%).
Your phenotype consists of all your traits that are visible to others, such as appearance and personality, as well as many traits that aren't. You have traits that you may have never guessed are part of your phenotype, including blood type, hormone levels and metabolic rate. In fact, your phenotype is simply the expression of your genes, or your genotype.
A variation of the same trait, such as type A or type B blood, is called an allele. For all genes that humans have, we get one allele from our mother and one allele from our father. In the case of sex determination, a male gets one X allele from Mom and one Y allele from Dad. For every one of our thousands of genes, there is more than one allele. In fact, sperm and egg cells are genetically unique from other sperm and egg cells from the same person. Because of this there are thousands or hundreds of thousands of possible "yous".
Alleles can be dominant or recessive, although genetics is often more complicated than that because a trait can be controlled by more than one gene. If an allele is dominant, the person will have the dominant trait. If an allele is recessive, the person needs two recessive alleles, one from each parent, to have the recessive trait. In genetics, dominant alleles are represented by capital letters, while recessive alleles are represented by lower-case letters.
We can use punnett squares to determine the probability of getting a certain phenotype when crossing the two genotypes of the parents. In the case of sex determination, the genotype of each phenotype, male and female, is known. An example of a punnett square used to determine the probabilities of getting male or female offspring is provided below. The possible genotypes of the offspring are in red in the center of the table. The alleles each parent can donate to the offspring are in bold on the outside of the table. Because there are 2 XX (females) and 2 XY (males) produced, either genotype is equally likely.
Punnett squares probability event outcome trials allele dominant recessive homozygous heterozygous phenotype genotype
For this science fair project, let's put on our jet packs and head to the planet "Planktonia" to perform some breeding experiments. Students, heed this warning: keep your breathing mask on at all times, and please, do not swim in the water!!
As an example, let's say you have chosen to make predictions about possible antenna types in the offspring given your zoomonster pairing. Your zoomonster has whip antenna (genotype dd), while your partner's zoomonster has bugle antenna (genotype DD). To predict the genotype of the offspring, set your punnett square up like this:
Welcome to the planet Planktonia!
It's time to create your Zoomonster planktonites!
All students heed this warning:
Do not swim in the water and please keep your breathing mask on at all times!!
Table 1. Coin toss traits.
Table 2. Genotype key.
You will notice that the dominant traits have two possible genotypes: a homozygous dominant (AA) and a heterozygous (Aa). To simplify, you are going to use the homozygous dominant genotype. The genotype for a zoomonster with the traits bell, gelatinous, cilia, one bugle antenna, two red eyespots, spiraling, solitary and non-bioluminescent is: aa/bb/CC /DD/ff/GG/HH/ii/jj
Figure 1. Some examples of zoomonsters
Figure 2. Zoomonster traits, part 1
Figure 3. Zoomonster traits, part 2
You should have a sense now that the basic principles of heredity can result in a diverse number of phenotypes. If you performed the coin toss project over and over, your zoomonster babies would probably all be different in some way. Similarly, you are different from your siblings and your parents are different from their siblings.
In step 5 of the procedure, you made punnett squares for 4 traits to determine the possible offspring phenotypes. You used the homozygous genotype when the trait was dominant. What did you notice about the offspring that resulted from each pairing? You may have noticed that when one parent has the homozygous dominant genotype for a trait, and the other parent has the recessive trait, the offspring will always have the dominant trait.
Questions & Answers
Given the information provided in the background section about the 23rd pair of chromosomes in humans, which parent determines the sex of a baby?
The father determines the sex of the baby since he can donate an X or Y chromosome, while the mother can only donate an X chromosome.
What is the probability of having a male baby?
Because it is equally likely that the father will donate an X or Y, the probability of having a male baby is ? or 0.5.
What is the probability of having a female baby?
We know the two probabilities of having a male or female are equal, so the probability of having a female is 0.5. The question can also be approached using the following reasoning. When there are only two outcomes, the individual probabilities of each outcome must sum/add-up to 1. Since the probability of having a male baby is .5, the probability of having a female baby is 1-0.5 = 0.5.
Make it Your Own
Use your imagination to design your own creatures for breeding experiments. First, pick the planet you will travel to. Next, pick 5 traits for the creature and determine the dominant and recessive phenotype for each trait. Set your table up the same way it was set up for the zoomonsters from Planktonia (see Table 1). Perform five coin tosses, one for each trait, and keep track of your outcomes (ie, heads or tails, dominant or recessive). Draw your creature! Finally, determine the genotypes of each phenotype in your table. Set your genotype table up like table 2. Remember, you can pick any letter of the alphabet to represent the genotype for a given trait, but the dominant form will have the capital letter, while the recessive form will have the lower-case letter. There will be two possible genotypes for each dominant trait. Finished? Excellent work!