Gregor Mendel & Punnett Squares Monohybrid & Dihybrid Crosses

How Mendel’s pea plants Helped us to understand Genetics Youtube video fives an overview of today’s lesson Time= 3:06 mins https://www.youtube.com/watch?v=Mehz7tCxjSE

Punnett Square Genotypes & phenotypes How do we use this Punnett Square? What would I write across the top and what would I write on the side? What would I write in the boxes? What does this chart show me? Why might this be useful?? Lets say parent1 : FF and parent 2:ff Can I write F along side and F along top? No you can’t split up the pair of alleles

Using a Punnett Square Predicts the likely outcomes of a genetic cross with the alleles taken from the parents Shows all the genotypes that could result from a given cross If we can figure out the offpsrings genotype we can predict their phenotypes On the board map out the P1,F1,P2, F2 generations and use the pea seed color again to demonstrate it

This is Mendel’s results for his pea plant experiments What does the column TRAIT refer to? (The gene we are looking at, the characteristic of the plant) What does the column DOMINANT vs RECESSIVE tell us? (that the characteristics on the left are dominant and the characteristics on the right are recessive so when we initially cross them all of our offspring will be the dominant trait, the recessive traits will appear only when we see the F2 offspring) What does F2 GENERATIONS mean? (these are the results of the second generation offspring, happens when we crossed the second parents, so two of the offspring from the first generation) Now what can we say about the RATIO column? Do we see and patterns?( looks like all the ratios are about 3:1)

Mendel’s F2 generations (Dominant : Recessive)

Using Probability Likelihood that a specific event will occur Probability = # of one kind of possible outcomes total # of all possible outcomes Probability of a specific allele in a gamete Represented as a fraction or ratio When he totalled his results he found that there was a unique ratio of yellow to green baby plants. These second generation plants produced baby plants that were in ratio of 3:1 yellow to green seeds. 75% of the offspring were yellow and 25% were green. Take a look at the cross of the F2 parents ( yellow x yellow= Yy x Yy) Write out the probability Fractions and ratios for the results So what can we conclude? When we are doing a heterozygous cross the offspring will always be in a ration of 3:1 (Dominant : Recessive)

What do you notice?? Look at this slide and see if there are any similarities? When you cross two heterozygous parents you get a ratio of 3:1 So if I give you Ff x Ff= can you predict the ratio of offspring? Mmx Mm? Dd x Dd? What would the genotypes be without using a punnett square? How many would look like the dominant trait? How many would look like the recessive trait?

Monohybrid Cross Cross involving a single trait All of the crosses involved the alleles for one gene only Mono= one hybrid=combination So a cross showing combination of alleles for one gene For example we looked at a cross of seed color- one trait but the two different alleles( yellow vs green) Or Flower color-one trait but two different alleles (purple vs white) Or plant height-one trait but two different alleles ( tall vs short)

Punnet Square Practice Board demonstrations of pea plant height (tall and small cross) P1,F1,P2,F2 Board demonstrations of pea plant color (purple and white) P1,F1,P2,F2

Divide class into two teams Team right is flower colour Team left is plant height A race to who can complete their cross first Rules: each person can only write one thing then someone else has to take a turn- Can only go up once Must write out all the alleles and stick up the correct phenotype

We look at crossing pea plants With two different traits? So What happens When We look at crossing pea plants With two different traits?

Cross that involves 2 traits Dihybrid Cross Cross that involves 2 traits Di= Two Hybrid=Combination Di=two hybrid= combination So a cross showing combination of alleles for two different genes Ex: A pea that is yellow and wrinkled crossed with a pea that is green and round

This is what the dihybrid punnett square chart will look like Across the top will be the allele combinations for the gametes of one parent Across the side will be the allele combinations for the gametes of the other parent It is a grid that is 4 x 4 So how many possible offspring will we look at? (16) So for probability with dihybrid crosses it will be ( / 16)

Bikini Bottom Genetics Bikini bottom genetics practice work sheet, to be done in class independently and passed in for marking If not enough time to complete they may take it home for homework There will be extra punnett square problems to be done for next class- only if you need the extra practice Although * PRACTICE MAKES PERFECT*

Parents= true breeding Dominant Yellow ( Y ) Round ( R ) Recessive Green ( y ) Wrinkled ( r ) So mendel crossed two true breeding parents who had round green peas and yellow wrinkled peas What would the parents genotypes be? RR yy x rr YY (round green) x (wrinkled yellow) Cross: round green peas and yellow wrinkled peas

Parents RRyy x rrYY F1 Generation (Use Foil) To figure out the F1 offspring use the foil method Review foil technique First Outside Inside Last This is what gives us the alleles to label each column/row So all of the F1 offspring are RrYy

Parents ( P2) RrYy x RrYy F2 Generation

Step 1 : Step 2: Step 3: Step 4: Determine the parental genotypes Determine the gametes (FOIL method) Combine the 2 different genes for each parent to represent a sperm cell and an egg cell Step 2: Set up a Punnet Square 4x4, place one gamete set from each parent on the top and side Step 3: These are the steps for completing a Dihybrid cross using a punnet square Step 4: Write the genotypes and phenotypes of each offspring (ratios)

Recessive= wrinkled ( r ) Consider this cross A cross between two heterozygous peas for round, yellow seeds. What are the parents genotypes? STEP 1 Dominant=Round ( R ) Recessive= wrinkled ( r ) Dominant= yellow ( Y ) Recessive=green ( y ) Rr Yy x Rr Yy

STEP 2 Rr Yy x Rr Yy FOIL method to figure out the gametes for each parent RY,Ry,rY,rY x RY, Ry, rY, rY