Introduction to Genetics Brought to you by: Your Favorite Science Teacher (that would be me)

Learning Goal: Students will be able to explain the basic principles of heredity by demonstrating the following… - distinguish between dominant and recessive traits - use human examples - use punnett squares 4= I know it & can teach it! 3= I know it 2= I know some of it 1= I know a little of it 0= What?

Heredity  The passing on of characteristics from parents to offspring Genetics  The branch of biology that studies heredity

Gregor Mendel  He was an Austrian monk  1 st person to study heredity  He was able to predict how traits are transferred from one generation to the next  Studied garden peas – He would transfer pollen from one plant to another plant with different traits  Controlled Experiment: only studied one trait at a time! (what a fantastic scientist!!)

The Pea Plants  Mendel studied several traits

Mendel’s Pea Experiments  Mendel chose pea plants because their traits were easy to see and distinguish.  He crossed plants with two different traits, for example purple flowers with white flowers.  He started his experiments with purebred plants.  Purebred plants ALWAYS produce offspring with the same trait as the parents. For example, if the parents are tall, all offspring will be tall. If the parents are short, all offspring will be short.

Let’s take a look at how that is… but first… some definitions!  Dominant: visible, observable trait of an organism that masks a recessive form of the trait. This trait is expressed ANYTIME the dominant allele is present. Expressed with a capital letter.  Recessive: a hidden trait of an organism that is masked by a dominant trait. This trait is only expressed if both alleles are recessive. Expressed with a lowercase letter

Dominant and Recessive Traits  It seemed to Mendel, that for each characteristic in peas, one trait was stronger than the other.  He called the “stronger” one, the dominant trait.  He called the “hidden” one, the recessive trait.

Learning Goal: Students will be able to explain the basic principles of heredity… - distinguish between dominant and recessive traits - use human examples - use punnett squares 4= I know it & can teach it! 3= I know it 2= I know some of it 1= I know a little of it 0= What?

And a couple more…  Allele: gene form for each variation of a trait (ex. Gene for short plants (t); gene for tall plants (T) )  Genotype: the gene combination of an organism, made up of 2 alleles (ex: Tt) – the capital/lowercase letter is extremely important!  Phenotype: the way an organism looks and behaves (ex: tall plants, white flowers, etc.)

And two more…  Heterozygous (hybrid): different alleles: Tt  Homozygous (purebred): same alleles: TT or tt – Homozygous Dominant: TT – Homozygous Recessive: tt No more definitions… I promise… well… at least for a couple more slides!

Understanding Mendel’s Experiments Part I (flower color) 2 alleles for purple PP Pp 2 alleles for white pp 1 allele for purple. 1 allele for white heterozygous homozygous

The result… One purple plant (PP) was bred with one white plant (pp). The result was 4 purple plants. Let’s look at a Punnett Square: Plant One  Plant Two pppp P PpPp Pp heterozygous

Plant One  Plant Two pppp Pp PpPp PpPp PpPp Pp P The genotypes in the boxes are the possible offspring of the two plants. Since each has the dominant allele (P) all the plants will be PURPLE. The PHENOTYPE would be PURPLE

Confused Yet?? Let’s take it one step further! Let’s cross two of the offspring from the first cross (remember, they were all Pp)

Understanding Mendel’s Experiment Part II 1 allele for purple 1 allele for white 2 alleles for purple PP 1 allele for purple 1 allele for white Pp 2 alleles for white pp Pp

The Result… Plant One  Plant Two PpPp P p PPPpPpppPPPpPppp One purple plant (Pp) was bred with one purple plant (Pp). The result was 3 purple plants and one white plant.

What is the phenotype of each plant??? Plant One  Plant Two PpPp P p PPPp Pppp Purple! WHITE!

Let’s take a more in depth look at genotype & phenotype  Genotype: Pp, PP, pp  Phenotype: Purple, white

What if…. G= green, g= blue Genotype:  GG  Gg  gg Phenotype:  Green  Blue

Learning Goal: Students will be able to explain the basic principles of heredity… - distinguish between dominant and recessive traits - use human examples - use punnett squares 4= I know it & can teach it! 3= I know it 2= I know some of it 1= I know a little of it 0= What?

Creating your own punnett square What are the possible offspring if you cross a short tailed cat (heterozygous- Ss) with a long tailed cat (homozygous – ss)? Short tails are dominant. Cat One  Cat Two ssss S s SsssSsssSsssSsss

Cat One  Cat Two ssss S s SsssSsssSsssSsss Possible offspring: Ss (short tail) or ss (long tail) What percent chance is there, if the cats produce ONE kitten, that it will have a short tail? 50% - a 2 out of 4 chance!

Try another… What are the possible offspring if you cross two 2-eyed monsters (heterozygous – Ee)? E= 2 eyes, e = 3 eyes Monster One  Monster Two EeEe EEEeEeeeEEEeEeee E e

Monster One  Monster Two EeEe EEEeEeeeEEEeEeee E e EE EE = two eyes Ee, Ee Ee = two eyes ee ee = three eyes

A Question to Ponder… Can two species have different GENOTYPES but the same PHENOTYPE???

ABSOLUTELY! 2 species can have different genotypes, but have the same phenotype. Example: TT= tall Tt= tall Both species have different GENOTYPES, but they are both TALL (phenotype!)

What questions do you have?

Learning Goal: Students will be able to explain the basic principles of heredity… - distinguish between dominant and recessive traits - use human examples - use punnett squares 4= I know it & can teach it! 3= I know it 2= I know some of it 1= I know a little of it 0= What?

F 1 Generation  Mendel called the parent plants the P generation.  He called the offspring from the parents the F 1 generation.  F is from the Latin word, filial, which means son.  When Mendel crossed pure pea plants with purple flowers with pure pea plants with white flowers, all the F 1 generation had purple flowers. P Generation F 1 Generation

F 2 Generation  When he crossed the F 1 generation peas with one another, only some of the offspring had purple flowers. These formed the F 2 generation.  Mendel found that in the F 2 generation, ¾ of the plants had purple flowers and ¼ of them had white flowers. F 1 Generation F 2 Generation x

Mendel’s Amazing Discovery Mendel did the same experiment with all 7 traits that he studied and discovered the same pattern each time: In the F1 generation, one trait was always hidden. That trait appeared in the F2 generation in about ¼ of the plants. Purebred P Generation Cross Pollination Hybrid F1 Generation Self-Pollination Hybrid F2 Generation

There is always an exception to the rule…

Codominance  In codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other. Roan Cow Is both white and red