CLASSICAL GENETICS II

Review for Lecture P101b

LAB THIS WEEK

• START in lecture room to go over instructions

• LATE-COMERS: come back at 2:30 (or 9:00). But no help after 4 (or 10:30)

• Report due Monday.• Focus on the logic. The “control” in genetics

experiments is the predicted ratio.

LAB LAST WEEK

• fix & resubmit by Monday:

• CODE on paper and grade sheet– 1= problems with graph;

– 2=wrong format;

– 3=other problems with written part;

– 4=graph + more problems

LAB LAST WEEK

• fix & resubmit by Monday: – MOST COMMON PROBLEM IS LOGICAL

THINKING.

– THE HYPOTHESIS AND RESULTS AND CONCLUSION MUST MATCH.

– DIVERSITY = COUNTING SPECIES.

THE HYPOTHESIS: BIG AREAS HAVE MORE SPECIES

– AND RESULTS : DID THE BIG AREA HAVE MORE SPECIES? Is that what your graph showed?

– AND CONCLUSION: DID YOUR CONCLUSION REJECT/NOT REJECT A HYPOTHESIS ABOUT species numbers BECAUSE OF THE RESULTS, WHICH WERE ABOUT species numbers ?

1 error?

SO WHY DID WE COUNT CRITTER INDIVIDUALS?

• AND IS THERE A WAY TO SHOW ALL THAT WORK IN YOUR GRAPH?

LAB LAST WEEK

• fix & resubmit by Monday: – MOST COMMON PROBLEM IS LOGICAL

THINKING.

– THE HYPOTHESIS AND RESULTS AND CONCLUSION MUST MATCH.

– DIVERSITY = COUNTING SPECIES.

Also you can re-do lab 1

• by Monday.

• Old and new grades will be averaged.

____1. An albino (white) bunny would have which genotype?

[a] AA. [b] aa. [c] Aa. [d] more

____2. A homozygous dominant genotype would be written as

[a] AA. [b] aa. [c] Aa. [d] more

____3. A heterozygous genotype would be written as

[a] AA. [b] aa. [c] Aa. [d] more

____4. A bunny with a heterozygous genotype would have

[a] colored fur. [b] white fur. [c] pale colored

5. Draw a Punnett Square showing a cross between two heterozygous

bunnies.

___ 6. What proportion of the offspring of the two heterozygous bunnies are heterozygous?

[a] 1/4 [b] 1/2 [c] 1/4 [d] all [e] none

___ 7. What proportion of the offspring of the two heterozygous bunnies are homozygous recessive?

[a] 1/4 [b] 1/2 [c] 1/4 [d] all [e] none

___ 8. What proportion of the offspring of the two heterozygous bunnies are albino?

[a] 1/4 [b] 1/2 [c] 1/4 [d] all [e] none

9. If the same two bunnies (the ones who were crossed in #5) produced 45 babies, how MANY of the babies are likely to be albino? (write the number)

__________11_________

• ____10. If two albino bunnies are mated, what is the probability that their first baby bunny will have colored fur?

• [a] 1/4 [b] 1/2 [c] 3/4 [d] all [e] none

11. How could we test the hypothesis that Petri, the Biology Department Bunny, is heterozygous for albinism? (Assume that we do not want to kill Petri in the experiment and also assume that we have been successful in reversing Petri's neutering surgery.) Briefly describe the experimental procedure and the predicted results of the experiment.

most important concept:

Genetic inheritance is based on probabilities of specific chromosomes and genes being present in the gametes which produce a zygote, the cell which multiplies to produce a new individual.

All possible problem types are based on two basic questions:

• Given these parents, what is the probability that an offspring will have __ genotype or ___ phenotype?

• Given this ratio of offspring, what are the most likely parental genotypes or phenotypes?

four possible types of crosses

• P-1 or homozygous cross (AA x aa)

• Hybrid cross (Hh x Hh)

• Test cross (Tt x tt) (Failed test cross) (Ff x FF)

PKU PROBLEMS(phenylketonuria: see the label on a diet drink)

• When a phenylketonuriac marries a person who does not have PKU and has been tested and found not to be a carrier, what is the probability that their first child will have PKU?

“RULES FOR WORKING GENETICS PROBLEMS”

1. For labs and predicted results on quizzes, the phenotype ratios are the results (or observations). Genotypes are hypotheses and conclusions (inferences and interpretations) and explanations for the phenotypes. Genotype includes words like dominant, recessive, heterozygous, sex-linked, etc. Genotype words cannot be in the “results” sections or in the predictions. Genotypes are only in the hypothesis and conclusion parts.

“RULES FOR WORKING GENETICS PROBLEMS”

2. Do a SIMPLE Punnett square for every problem. If it’s a dihybrid type problem, do two Punnett squares and multiply the fractions. If the problem is more complex, do more Punnett squares.

“RULES FOR WORKING GENETICS PROBLEMS”

3. For almost every problem, begin by writing down the phenotypes and genotypes like this example:

– Sickle-cell aa

– Normal Aa or AA

– (Carrier Aa)

“RULES FOR WORKING GENETICS PROBLEMS”

• 4. For almost every problem, symbolize or reiterate the question. For example, if it asks how many of the children will be carriers, write down something like this:

– ? Aa

• This is just a good habit to make sure you’re aiming toward the answer and not wasting time calculating how many are not carriers or something else not needed for answering the question.

“RULES” FOR WORKING GENETICS PROBLEMS

1. Results = observations = phenotypes, not….

2. Keep Punnett squares simple.

3. Write genotype/phenotype chart first

4. Make sure you’re answering the question.

5. Don’t even think about ….

Dihybrid cross

Dihybrid = 2 kinds of genes

• Color + texture. Do 2 Punnett Squares.

• Then apply the product principle of probability (multiply)

Bad high school method.

• Don’t do this

• It’s good for explaining, like theprevious slide

• but not goodfor working problems

Cystic fibrosis is recessive. Sickle cell anemia is recessive

• If Frances and Francis are both heterozygous for both cystic fibrosis and sickle cell anemia, – what is the probability that their first child will

have cystic fibrosis?– what is the probability that their first child will

have sickle cell anemia?

Cystic fibrosis is recessive. Sickle cell anemia is recessive

• If Frances and Francis are both heterozygous for both

cystic fibrosis and sickle cell anemia, – what is the probability that their first child will

be a carrier of both diseases?– What is the probability that their second child

will be homozygous dominant for both diseases?

Polydactyly is dominant

• Two 6-toed dogs mate and have 7 puppies, 6 with 6 toes but one with normal toes. What is the most likely genotype of the parent dogs?

Polydactyly is dominant

• A 6-toed dog, Fluffy, mates with a normal-toed dog, Ralph. They have 14 puppies, all with 6 toes. What are the most likely genotypes of the parent dogs?

Polydactyly is dominant and albinism is recessive

• An albino dog with normal toes, Archie, mates with a yellow 7-toed dog, Precious. Precious was sired by a

normal-toed albino, Fido. If Archie and Precious have 12 puppies, how many are likely to be yellow and normal-toed?

Polydactyly is dominant and albinism is recessive

• An albino dog with normal toes, Archie, mates with a yellow 7-toed dog, Precious. Precious was sired by a

normal-toed albino, Fido. If Archie and Precious have 12 puppies, how many are likely to be yellow and normal-toed and female?