Population Genetics  A population is any group of organisms that are able to interbreed with one another.  Gene frequencies represent how often alleles occur in a given population. If the gene frequency for the ability to roll your tongue is 35%- that means that in successive generations roughly 35% of the population would be able to roll their tongue.

Population Samples  As we evaluate traits in a given population, the more individuals that are surveyed the greater the accuracy.  With more samples: More likely to assess all allele combinations Accuracy increases

Introduction to Inheritance Objectives:  Describe how traits are passed from one generation to the next  Describe Mendel and his contribution to genetics.’  Define and give examples of phenotype and genotype

Mendel’s Contribution  Gregor Mendel was a monk who experimented with pea plants. His experiments with these simple plants changed our understanding of genetics forever.  Mendel studied the traits, or specific characteristics that each type of pea plant possessed.

Mendel’s Contribution  He then crossed one pea plant with another. This cross produces the first filial generation offspring, or the F1 generation. The plants that Mendel produced from these crosses are called hybrids, because they are the offspring of crosses between parents with two different traits.

 When you cross a wrinkled pea and a smooth pea… the result is a smooth pea

Mendel’s Experiments  Each time that Mendel did this he was intentionally crossing pea plants to see what traits the offspring would have. Example - Mendel crossed a round pea producing plant with a wrinkled producing plant the outcome was a round pea.

Mendel’s Experiments Continued  Mendel continued to experiment with the pea plants and found that if he crossed specific traits then he would get the same results.  This got Mendel thinking… There must be something behind these results.

Mendel’s Conclusions  Mendel concluded that there are factors that are passed from one generation to the next, called genes.  He determined that there are different forms of genes, called alleles.  These alleles caused some of the pea plants to be tall and others to be short.

Principle of Dominance  He came up with the principle of dominance that states, that some alleles are dominant and some are recessive.  An organism with a dominant allele for a particular form of a trait will always have that form. Example: If a pea plant has a dominant allele for height that is tall, the plants produced will always be tall. These are represented using CAPITAL letters.

Principle of Dominance Cont.  An organism that has a recessive allele for a trait, will only have that form if the dominant allele is not present. Example: If a plant has the recessive allele for short height, then only offspring yielded from two plants having this allele will produce offspring that are short. These are always represented by lowercase letters.

Mendel’s thinking again…  Mendel wondered what happened to the recessive alleles when a dominant allele was present, so he allowed the plants to be crossed a second time, producing a second filial or F2 generation.

What Mendel found…  The results of crossing the F1 generations were that both types of plants were produced, tall and short.  This indicated that recessive alleles don’t disappear when the dominant allele is present.

What it all means…  Mendel’s contributions allow us to understand how specific characteristics, or traits, are passed from one generation to the next.  His research was also the first to explain dominant and recessive alleles.

How is it used?  We use Mendel’s ideas to predict crosses of animals, insects, plants and now humans.  This allows us to see what the phenotype, the physical characteristics of an offspring, as well as the genotype, the genetics of an offspring might be before they are crossed.

Phenotype  With your partner brainstorm phenotypic characteristics that you could possess below.

Genotype  With your partner brainstorm genotypic characteristics that you may possess below.

Allele Combinations  If you are short… What is your phenotype? What is your genotype?  Figuring out your genotype can be a little more tricky then figuring out your phenotype. Since your phenotype is your physical characteristics you can usually see them.

Allele Combinations  Your genotype, or genetic make-up is not something that you can see, this makes it more difficult to point out.  If you are short your genotype would have to be tt.  How do you know? Tall is dominant for height. You must have no dominant alleles if you are not tall.

Allele Combinations  What if you are tall? If you are tall, you can have two possible gene combinations. TT- Two dominant alleles Tt- One dominant and one recessive allele. Remember the recessive allele t is masked by the dominant allele.

Allele Combinations  When you have two alleles that are either both dominant or both recessive this is called homozygous. TT (homozygous dominant) or tt (homozygous recessive)  When you have two alleles that are not the same, such as one dominant and one recessive this is called heterozygous. Tt

Punnett Squares Objectives:  Complete a punnett square  Define the essential vocabulary  Determine the probability of specific traits from a punnett square

Vocab. Revisited  Define the following from your notes: Homozygous Heterozygous Dominant Recessive Allele

Punnett Squares… What are they good for…  A punnett square is a diagram in which gene combinations can be determined.  Across the top and side of the punnett square you will find the genotype of the gametes produced in the F1 generation.  Remember: Capital letters represent dominant alleles Lowercase letters represent recessive alleles

Starting off easy…  Punnett squares are used to predict the genotype and phenotype of offspring.  Complete the punnett square below, using the principles of math. A A A A Parent One Parent 2

A A A A Each square represents a 25% probability of that phenotype/ genotype being expressed If this were a mutliplication table as in math, what would you write in each of the squares??

Practice time Using the white boards, create the punnett square that answers the question posed by the teacher.

A little harder now…  In guinea pigs a rough coat (R) is dominant over smooth (r). If a heterozygous rough guinea pig is mated to a rough animal that is also heterozygous, what is the chance that they will produce a smooth-coated guinea pig?

Fill in the punnett square with the given information… Given Information: Parent 1: Heterozygous Rough coat Rr Parent 2: Heterozygous Rough coat Rr Rr R r RRRr rr

What does this punnett square tell you…  Probable genotypes of the offspring produced in the F2 generation ______ ______  Probable phenotypes of the offspring produced in the F2 generation ______ ______

How do you determine probability?  Each piece of the punnett square represents a 25% probability of having that trait. Rr R r RRRr rr 25%

 If you have two genotypes that represent the same phenotype then you would add the two genotypes together.  In this example: Rough Coat 25%+25%+25%=75% Smooth Coat 25%  At the end the probability should add up to 100% 25% + 75% = 100% Rr R r RRRr rr 25%

Now answer the question  In guinea pigs a rough coat (R) is dominant over smooth (r). If a heterozygous rough guinea pig is mated to a rough animal that is also heterozygous, what is the chance that they will produce a smooth-coated guinea pig? Answer:________________________

A little harder still…  Tall tomato plants are produced by the action of a dominant allele (T) and dwarf plants by its recessive allele (t). A homozygous tall plant is crossed with a dwarf tomato plant.  Use a punnett square to answer the questions that follow.

Question 1.  What are the two genotypes of the parents? Parent 1: ______ Parent 2: ______  Complete the punnett square below.

Question 2.  What is the probability of having an offspring that is a dwarf?  What is the probability of having an offspring that is tall?

Even Harder…  A black coat in cocker spaniels is dominant (B), while red coat color is recessive (b). A black male is mated to a red female and produces a litter of eight pups: four black and four red. Determine the genotypes of the parents.

What do you know?  What must the phenotype of the red female be? Fill this information in on the punnett square.  Now fill in the rest of the information that you know. bb b bb b

Working through it  What must go in the punnett square to make this statement true: four black and four red are produced? Fill in your punnett square to make this statement true.

Reasoning it out…  What is the phenotype of the father? bb Bb bb Bb ? ?

 You have now answered one of the hardest type of punnett square questions of this type… Congrats!  Now complete the practicing with punnett squares packet.