GENETICS

WHAT IS A GENE?? What are some things that our genes might code for? A GENE is found on a chromosome. It is a sequence of DNA that “codes” for a trait. That means it holds the information for something about us, like eye color, or skin tone, or height, or how to make bone. What are some things that our genes might code for?

WHAT IS AN ALLELE? An ALLELE is the part of the gene that holds the actual trait. There are TWO alleles for every gene. You get one from your mom and the other from your dad.

WHAT IS AN ALLELE? For example: I have a gene for eye color. The allele from one parent is for brown eyes, the allele from the other parent is for blue eyes. Alleles are the different variations that the gene can have.

Traits can be either DOMINANT or RECESSIVE. Depending on which ones you get from your parents will determine which ones you see. Your GENOTYPE tells you what genes you have. Capital letters represent DOMINANT, and lower-case letters represent RECESSIVE. Being you get one from mom and one from dad, you have 2 letters for each trait. They can look like this: BB Bb bb In the first one, you got a dominant trait from both parents, in the second one, you got a dominant trait from one parent and a recessive trait from the other, and in the third, you got a recessive trait from both parents.

Now let’s say that Black hair is dominant to Blonde hair. So Black is “B” and blonde is “b”. If you have “BB” that means you got Black hair from both your parents, so your hair is Black. If you have “Bb” that means you got Black hair from one parent, and Blonde from another. Because Black is dominant to Blonde, your hair is Black. If you have “bb” that means you got Blonde hair from both your parents, so your hair is blonde. PHENOTYPE is what you see. So your phenotype is either Black hair or blonde hair.

BB Bb bb So our Genotype determines our Phenotype. What genes we get from our parents determine what we look like. But what decides which genes we get? Unfortunately, it is completely random, but we can predict the odds of a single trait by doing something called a “Punnett Square”.

B BB b Bb BB Bb How do we do it? If these two people were to have a child, what would it look like? Let’s find out! How do we do it? We start by making a Punnett Square, which is like a multiplication table. We put the letters from one parent along the top, the letters from the other parent on the side, and multiply. We do this because the child can only take ONE from each parent. What’s the percent phenotype for this child? What about the percent genotype? B BB b Bb

B b BB Bb bb Bb Bb What are the phenotypes these parents can have? If these two people were to have a child, what would it look like? Let’s find out! What are the phenotypes these parents can have? What’s the percent phenotype for this child? What about the percent genotype? B b BB Bb bb

Different genotypes have different names. BB is called HOMOZYGOUS DOMINANT Bb is called HETEROZYGOUS bb is called HOMOZYGOUS RECESSIVE BB Bb bb

WHERE DID WE DISCOVER THIS?? Gregor Mendel was a monk who experimented with pea plants. He found that if you took certain peas with certain traits, like color or texture, and crossed them to make new peas, you could predict the odds of the traits of the next generation of peas. This was the basis for Punnett Squares, and genetics.

LABELING GENERATIONS The first set of parents we look at are called the PARENT GENERATION, or P-GENERATION. The first set of offspring is called the F1-GENERATION. The offspring of the offspring (grandchildren of the P-Generation) is called the F2 Generation

LAWS OF HEREDITY LAW OF SEGREGATION Whenever gametes form, only ONE allele for each trait is given to that gamete. Remember, you carry 2. One from mom, one from dad. When you make a new sperm/egg, you only get to give ONE of those, and it’s random. LAW OF INDEPENDENT ASSORTMENT When all your alleles separate, they do so individually. Meaning, nothing is grouped together. Your allele for hair color doesn’t stay with your allele for hair texture. Everything is on its own, and random.

This means our Punnett Square is going to be bigger. BBAA BBaa bbAA bbaa Sometimes, we have more than two phenotypes for a trait, like hair color. We can have black, blonde, brown, or red. This means that more than one gene controls this trait. This means our Punnett Square is going to be bigger.

BA Ba bA ba BBAA BBAa BbAA BbAa BBaa Bbaa bbAA bbAa bbaa What if these to parents had a kid? They can only give ONE allele from every gene (pair), so if they have TWO pairs for hair color, they are going to give TWO alleles. Let’s see what the Punnett Square would look like. BbAa BbAa BA Ba bA ba BBAA BBAa BbAA BbAa BBaa Bbaa bbAA bbAa bbaa

BA Ba bA ba BBAA BBAa BbAA BbAa BBaa Bbaa bbAA bbAa bbaa So which phenotype will we see? Remember, homozygous dominant and heterozygous genotypes will give you the same phenotype! BA Ba bA ba BBAA BBAa BbAA BbAa BBaa Bbaa bbAA bbAa bbaa

B BB b Bb NAMING MY PUNNETT SQUARES BA Ba bA ba BBAA BBAa BbAA BbAa Only working with one gene? You just did a MONOHYBRID CROSS. BA Ba bA ba BBAA BBAa BbAA BbAa BBaa Bbaa bbAA bbAa bbaa Working with 2 genes? You did a DIHYBRID CROSS.

EXCEPTIONS TO THE RULE CODOMINANCE When neither trait is dominant, so you see BOTH expressed in the phenotype INCOMPLETE DOMINANCE When one trait is not completely dominant over the other, so you see a blend of both traits

WHAT ABOUT MUTATIONS? Mutations occur when there is an error in DNA replication. The mutation becomes a part of the person’s genetics, and CAN be passed on to children!

Some mutations can be seen. However, some mutations cannot!