5.06Genotypes and Phenotypes Need a little help?
Important vocabulary to know Alleles are corresponding pairs of genes located on an individual’s chromosomes . Together, alleles determine the genotype of an individual. The Genotype describes the specific genetic make up of an individual. A person’s genotype tells us exactly what Alleles/genes they have. You cannot see someone’s genotype. Phenotypes are the observable traits of an individual which the individual’s genes (alleles) have expressed.
Let’s take a look at some Phenotypes: This image shows a widow’s peak, this means the hair line on the forehead dips down into a peak. You either have the phenotype of a widow’s peak or you don’t. If you don’t, your hair line on your forehead goes straight across without the point. AA or Aa The second image shows an unattached earlobe. People either show a phenotype of an attached earlobe or an unattached earlobe. Now lets’ talk about the Genotypes. See the letters above each picture? Those letters are the individual’s GENOTYPE and they represent the Genes or Alleles that determine the observable trait (phenotype) in the picture. Alleles are a PAIR of genes which is why you see the letters in groups of 2. You may be wondering why the genes are in pairs, this is because one of the genes came from the mother and one of the genes came from the father. But why are there upper case letters and lower case letters? I’m so glad you asked.
Dominant and Recessive traits You noticed that there are Uppercase letters and Lowercase letters . Again, these letters are the Genotype When dominant alleles are present, the information they carry is always expressed. In other words, a dominant trait is always observed if a dominant allele for that trait is present. So, if you have the genotype WW, will you have the widow’s peak phenotype? ABSOLUTELY!!!!
An individual can have 1 dominant gene and 1 recessive gene in their genotype (ex: Ww) depending on what genes they got from each parent. So, if you have the genotype Ww, will you have the widow’s peak phenotype? ABSOLUTELY!!!! Because you have one dominate gene (W) you will have the phenotype. When two recessive alleles are present, the recessive trait is expressed. So, if you have the genotype ww, will you have the widow’s peak phenotype? NEVER!!!! Because you have got recessive genes (w) from both your parents.
Who is the heir to the fortune! A rich couple that died in a traffic accident 10 days ago has one heir to their fortune. Five people claim to be the lost heir of the rich couple and they have filed a claim to the family’slawyer to receive their rightful inheritance. By using genetic evidence and looking at the parent’s Phenotypes, you will help the family lawyer to determine which individual is the rightful heir. Father Mother The Claimants
First, let’s look at their Earlobes. Having attached or detached earlobes is a trait you inherit from your parents. In this example we are using an Upper case A to represent the Dominant Gene and a lower case a to represent the Recessive Gene. Read the information below and see if you can answer these questions. 1. Do the parents have attached or detached earlobes?2. What about the claimants? Attached or detached earlobes?3. If you have detached earlobes, what possible genotypes can you have?4. If you have attached earlobes, what possible genotypes can you have?
Both parents have Attached earlobes. Since we know that having attached earlobes is a Recessive trait we can determine that the parents can only have the recessive genes for this trait. Therefore, the only possible genotype that the parents can have is aa. If both parents have the recessive trait then they can only pass on a Lower case a (recessive gene) to their offspring. Because we know this information, it will be easy to rule out one or more claimants by simply looking at their earlobes. If a claimant has DETACHED Earlobes, they can’t be the offspring of this couple. If a claimant has DETACHED earlobes, then they have at least one Dominant gene or Uppercase A in their Genotype. aa aa a a aa aa aa aa Aa or AA
Now let’s look at another phenotype, Dimples. Having Dimples is a Dominant Trait. Look over the information below and see if you can answer the following questions If an individual has dimples, what is their possible Genotype? (remember, these are letters and you can have more than one possible genotype) Do the parents have dimples or not? What is there genotype? Can you eliminate any claimants based on this phenotype (dimples or no dimples?
This is a tough one. Let’s take a closer look Both the parents have Dimples. This means that they have the Dominant Trait. This also means that they must have at least one Dominant Gene in their Genotype. Both Mom and Dad could have a DD or a Dd as their Genotype. What does this mean for the offspring? Is it possible for these Parents to have offspring with out dimples? The answer is Yes. For example if both Mom and Dad have a Genotype of Dd then it is possible for them to pass on the recessive traits. A Lower case d can come from Mom and a Lower case d can come from the dad which would produce an Offspring WITHOUT dimples (dd). Cool huh?
You are doing great! Keep it up! We have a few more phenotypes to look at. Remember the Widow’s peak? Take a look at the info below and see if you can answer the following questions. Is having a Widow’s peak a Dominant or Recessive trait? If you have a Widow’s peak, what are your possible Genotypes? If you don’t have a Widow’s peak, what is your possible Genotype? Can you eliminate any claimants based on this Phenotype?
Last Phenotype: Blood Types A, B, AB or O This is a tricky one! For blood types we do not worry about Uppercase or Lowercase letters. A and B are the Dominant genes for blood type and O is considered the recessive gene. A and B can be co-dominant. For example: If a mom has type A blood and the father has type 0 blood then the offspring of this couple with have type A blood because the A from the mom is dominant over the dad’s recessive O gene. A + O = O Mom has Blood type A Genotype AA Dad has Blood type O Genotype OO Son gets A from Mom and O from Dad. A is Dominant so the son has blood type A Son’s Genotype is AO
Another Blood type example A and B can be co-dominant. If a mom had type A blood and the dad had type B blood then the offspring of this couple could have type AB blood because both A and B are dominant genes and they form a sort of team so that both A and B are present. They co-dominate. A + B = AB Mom has Blood type A Genotype AO Dad has Blood type B Genotype BO Son get’s A from mom and B from Dad. Both A and B are Dominant traits so son has type AB blood.
Blood type: Now that you know a little bit more about what Alleles determine an individual’s blood type you should be able to eliminate another claimant based on their blood type. Take a look at the Mother’s blood type and Father’s Blood type. The Father is AB and the mother is O. Which one of the3 claimants below can you eliminate as the heir?
DNA test The DNA test is final test to determine the true heir to the fortune. When DNA from the offspring is compared with the DNA of the Parents, specific chromosomes are compared. If certain chromosomes match up then there is a very high probability that the individuals are related.
Final Summary: You should now be ready to write your final report for the family attorney. Your final report should be at least one well developed paragraph that identifies the heir to the fortune. Your final report should state…. if the heir is male or female, the heir’s possible genotypes and phenotype for earlobes the heir’s possible genotypes and phenotype for dimples. the heir’s possible genotypes and phenotype for widow’s peak. Include the heir’s blood type and the results from the DNA test.