PowerPoint Breakdown:

Slide 2 and 3: Have the students write two or three sentences on the importance of the pictures

on the slide (Mendel worked with pea plants to study genetics; peas can be green or yellow,

smooth or round; all species, like the butterfly, have genes that make them different from

each other). After discussing their thoughts, ask the students important vocabulary (generations

= parental and filial; hybrids = cross) from Mendel’s work and questions about simple genetics

(What is genetics = study of inheritance; Why is it important = determines what we look like).

Walk students through Mendel’s first cross. The parents are the first plants that are crossed

(what is the difference between the two parents = one is smooth and one is wrinkled; what

causes the smooth one to be smooth = SS; what causes the wrinkled one to be wrinkled = ss).

When the plants are crossed, they create the filial generation, which means offsprings – literally,

it means son. What do these peas look like (all are smooth). What do these have in common

with the smooth parents (both have big S). Yes, the big S means that it is dominant, and it

overshadows any little letters. However, just like you get your genes from both mom and dad,

the filial generation also contains a little s. If we cross the peas from the filial generation, what

do we get (3 smooth, 1 wrinkled). What does the big S mean? (dominant) What does the

small s mean? (recessive)

Slide 4: Ask students, what does it mean that inheritance is passed down between generations

(some genes come from mom, others come from dad); discuss the difference between genes

and alleles – genes are the traits, alleles are the different ways those traits express themselves.

For example, a gene could be hair color. An allele would be brown, blonde, red, etc. Can you

think of an example of a gene with its alleles? (Gene = eye color, allele = brown, blue, green,

etc.). Explain the difference between dominant and recessive – dominant means the

characteristic is expressed, recessive means the characteristic can be hidden. How do you know

which trait is dominant (big letters) How do you know which trait is recessive (small letters)

The way the letters are combined are called the characteristics genotype. They way the

characteristic looks is the phenotype. A good way to remember is that genotype can be broken

down into the TYPE of GENE and the ph in phenotpe relates to physical characteristics.

Slide 5: Mendel studied seven different plant characteristics. In this chart, it lists which are

dominant and which are recessive. Lets go ahead and think of the genotype for these

characteristics. Flower color is the first the gene. What letter should we give it (C). Okay, now

if purple is the dominant trait, what would the letters look like – remember, there are always two

letters (CC) Can it look any other way? (Cc) If there are blank stares, follow with remember,

what happens if the recessive is hidden, what does that look like? (Cc). Now white is the

recessive trait, what would that look like (cc). Now, what I would like you to do is discuss

within your groups the genotypes for each the six other traits. Remember dominant traits will

have TWO genotypes, recessive traits will only have one.

Slide 6: How many of you have studied probability in math class? Can someone explain it?

(The chance that something will happen). Good, now in genetics, it is all probability or

chance. There is never a 100% chance of a certain outcome; however, there can be a 100%

chance of something not occuring. What are some ways we express the chance of something

happening? (By percentage). Okay, and a percentage is basically what (a fraction). If blank

stares, prompt with, remember it is something out of 100 (a fraction). Now, there is one other

way to express probability. Has anyone heard of a ratio? How are ratios expressed (with a :)

Good. So, if we were to say that something ways a two to one, how would you write it (2:1)

Slide 7: Punnet Squares are the way we work out the probability, or chance, of a cross between

two parents. Before we begin, there is some terminology that we need to go over. Some of this

you have seen before. What does homozygous mean (the same) What does heterozygous mean

(different). Good, now lets think what this means in terms of genotype. If homozygous means

they have to be the same, then they have to both be big C big C or what? (little c little c) What

would you guess the genotype of heterzygous would be (big C little c). Just to review,

phenotype is what type of characteristic (physical) and gentoype is the type of (gene). How do

we represent genetoype (with letters). Lets look at the different offspring we have in this

Punnett square. What is unique about this one is that we have combined two different genes, the

one for color and the one for skin. We have to look at both genes together. So, how many of

these are Smooth/Yellow (9). Good, now how many possible offspring are there – count up each

block (16). Okay, so what is the percentage (about 56%) Good. How else could we write it

(9/16) and how about a ratio (9:16). Good, now in your groups, do the percentage, fraction, and

ratio of Wrinkled/Yellow, Green/Round, and Green/Wrinkled. Discuss results. Now, if I said

what is the ratio of Smooth/Yellow to Wrinkled/Yellow, to Green/Round, to Green/Wrinkled –

what would it be – how many of each are there – (9:3:3:1). What color do you think is dominant

(Yellow) what skin type do you think is dominant (Smooth). Now, I’m going to give you a

Punnett Square idea – each of you will be crossing different things and writing the probability in

different ways. When you finish, come put them on the board.

Slide 8 and 9: Show Mendel’s Punnett square on Yellow/Round Peas crossing with

Green/Wrinkled Peas. His cross was done with true-breeding plants – plants that are either

homozygous dominant or homozygous recessive. What does homozygous mean (same), so

for homozygous dominant both the letters are (big) and for homozgous recessive both the ltters

are (small). Unlike the monohybrid (mono = 1) crosses you have just done, he crossed two

different traits – color and skin appearance. What do you think this cross is called….if mono

was 1, then 2 will be (dihybrid) When you do this, you have to mutliply the possible

combination of genotype. So for dominant RRYY, you would multiply the first R by the first Y

which equals = (RY), the first R by the second Y, the second R by the first Y, and then the

second R by the second Y, which equals = (RY). Now the recessive is rryy. How do multiply it

out (first r by first y, first r by second y, second r by first y, second r by second y) This is our

first cross. So, we set up the different combinations around the top and down the side of

our Punnett Square, like you did in yours. Now, what is the only outcome? (RrYy) After this

first cross, Mendel crossed the offsprings together. So now we have RrYy – what different

combinations can we have? (RY, Ry, rY, and ry) Now, we put these across the top and down

the side and solve out Punnett Square. From the diagram, how many are Yellow/Round, how

can you tell (9 – because they have a Y and an R). In your groups, determine how many are

Yellow/Wrinkled, Green/Round, Green/Wrinkled. Discuss answers. Now what we have done is

distinguised the what the offspring look like, which is what, genotype or phenotype

(phenotype). Now lets do the genotype. What we really are looking for is the amount

of offspring that are homozygous – how many are homozygous Yellow/Round (1). In your

groups, determine how many are homozygous Yellow/Wrinkled, Green/Round,

Green/Wrinkled. Discuss answers.

Slide 10: Mendel got very lucky in his pea plant studies, because the characteristics Mendel

choose segrated independently of each other, we call this independent assortment. This basically

means that when the gamete cells split in meiosis, the whole trait will separate into the new

cell. For example, the trait for eye color normally segrates independently – making both eyes

the same color. However, if it doens’t, then we see people with two different eye colors.

Slide 11 and 12: During this short video – its only a minute long – I want you to write down 4

important conclusions from Mendel’s studies. Show rap video of Mendel’s theory; remind

students that this could be an option for the extra credit on the mutations lab! Discuss their

conclusions with Mendel’s – clarifying any descrepencies. Why do you think meiosis is

important for Mendel’s studies (because it depends on the separation of chromosomes to

determine what we look like)

Slide 13-16: Remind students that nothing in science is 100% true in all circumstances. Not all

characteristics follow the rules of dominance. Remember in normal dominance, a dominant red

flower and recessive white flower, will produce a red or white flower. For normal dominance,

red + white = red or white. In codominance – both the dominant and recessive trait contribute to

the appearence. So in this flower, we have a dominant red and recessive white – when they

combine they produce a flower that has both colors. A nice way to remember this is that in

codominance, red + white = red and white. In incomplete dominance, the heterozygous flower

will have the two traits mixed together. So red + white = pink. Many traits, are not black and

white though. For example, with hair color, there are multiple alleles that contribute to the gene

– this is why no two people have the exact same hair color. Sometimes, a trait will have

different genes that contribute. The easiest way to remember this is through the skin color. We

all have red genes, yellow genes, and brown genes. Its the combination of these three genes that

lead to an individuals skin color.

Slide 17: They way we look is not just dependent on our genes. The enviornment plays a big

factor. Lets discuss the articles you found. In your groups, write 10 things to turn in as a group

about the effect of the environment. I woudl like each group to present their findings – if one

group has said something on your list – talk about something else. If all your points to talk about

are gone, don’t worry – I have your sheet to see what you’ve written down.