Biology 22: Genetics and Molecular Biology
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Transcript of Biology 22: Genetics and Molecular Biology
Biology 22: Genetics and Molecular Biology
Spring Semester 2008
Enrollment
Biology 22 is currently full.
Please sign-in on the sheet to your left (next to your name) if you are in the class.
Please sign-in on the sheet to your right if you want to add the class; include lab section.
Enrollment
If you want to add, you must show up on the first lab day to see if a spot is available.
If a places are available, names will be chosen on Friday in lab.
All decisions to determine if places are available and the handing out of “add numbers” will be completed by this Friday.
Syllabus Please read through carefully. Brief discussion of key points Summary of key points:
Bio 21 (or equivalent) & Chem 11 pre-requisites English 1 advisory Bio 22 covers genetics and molecular No make-up exams or assignments
Ch 3 Basic Principles of Heredity
Outline
Mendelian Genetics & monohybrid crosses Mendel’s 1st Law
Predicting Genetic Outcomes
Punnett Squares Formulas for more complex problems
Other genetic concepts
Test Cross Incomplete dominance
IN LAB ON FRIDAY
Di-hybrid Crosses
Chi-Square Test (you will apply this test to the data collected).
Gregor Mendel
1822-1884
homozygotes
F1 filial
MONOHYBRID CROSS
F2 3:1 ratio
(Or the other way around!)
Reciprocal cross
heterozygotes
MONOHYBRID CROSS
The disappearance of trait in F1?
The re-appearance of trait in 25% of F2?
But why did Mendel observe…
Mendel reasoned that: 2 alleles exist
Alleles are either Dominant Recessive
wrinkled
Round
1. Each trait is governed by two factors – now called 1. Each trait is governed by two factors – now called genesgenes..
2. Genes are found in alternative forms called 2. Genes are found in alternative forms called allelesalleles. .
3. Some alleles are 3. Some alleles are dominantdominant and mask alleles that are and mask alleles that are recessiverecessive..
Thus Mendel proposed:Thus Mendel proposed:
Mendel’s 1st Law Principle of Segregation
A diploid organism has 2 alleles for a characteristic.
The alleles separate and the gamete receives only one
of these alleles.
Alleles separate in equal proportions.
Review concept: Segregation during meiosis
Be able to identify
Homologous chromosomes
Alleles
PUNNETT SQUARE
(backcross example)
1) a method to predict genotypic and phenotypic ratios
Round seeds versus wrinkled seeds
Parentals: Parentals: RR x rrRR x rr
R R r r R R r r
RR
RR
r r r r
F1 x F1: F1 x F1: Rr x RrRr x Rr
R r R r R r R r
½ R½ R
½ r½ r
½ R ½ r ½ R ½ r ¼ RR¼ RR ¼ Rr¼ Rr
¼ Rr¼ Rr ¼ rr¼ rr
RrRr RrRr
RrRr RrRr
2) Rules of probability to predict outcomes
Independent eventsordered
Mutually exclusive
and
either/or
1/6 x1/6 =1/361/6 + 1/6=2/6=1/3
Genetic applications What is the P that two heterozygous parents
have 3 children ALL with albinism?
What is the P that they have 3 children, 1 with albinism and 2 with normal pigmentation? ANN or NAN or NNA
9/64 + 9/64 + 9/64 = 27/64
¼ x ¼ x ¼ = 1/64
What is the P that they have 5 children 2 with albinism and three normal pigmentation? “unordered event”
P = n!/s!t! asbt
P = 5!/2!3! (1/4)2 (3/4)3 = 0.26
Binomial Rule
A “Test Cross” What is a test cross?
Known recessive genotype X unknown genotype
What do we learn from a test cross?
Intermediate expression of traits.
Incomplete dominance
Know these terms Gene Allele
Dominant Recessive
Locus Genotype Homozygote Heterozygote Phenotype Incomplete Dominance Character
End of lectureclick to practice some
problems.
End of lectureclick to practice some
problems.
Practice Problems Try your skills at the following problem.
First some rules & concepts are reviewed.
Problem
Powerpoint will be updated with answers and posted on ecompanion.
Note: When solving genetics problems
1. Convert parental phenotypes to genotypes
1. Use Punnett Square to determine genotypes of offspring
1. Convert offspring genotypes to phenotypes
Using Probability in Genetic Analysis
1. Probability (P) of an event (E) occurring:1. Probability (P) of an event (E) occurring:
P(E) = P(E) = Number of ways that event E can occurNumber of ways that event E can occur
Total number of possible outcomesTotal number of possible outcomes
Eg. P(Rr) from cross Rr x RrEg. P(Rr) from cross Rr x Rr 2 ways to get Rr genotype 2 ways to get Rr genotype 4 possible outcomes 4 possible outcomes P(Rr) = 2/4 = 1/2 P(Rr) = 2/4 = 1/2
Using Probability in Genetic Analysis
2. Addition Rule of Probability – used in an “either/or” situation
Eg. P(Rr or RR) from cross Rr x Rr Eg. P(Rr or RR) from cross Rr x Rr 2 ways to get Rr genotype 2 ways to get Rr genotype 1 way to get RR genotype 1 way to get RR genotype 4 possible outcomes 4 possible outcomes P(Rr or RR) = 2/4 + 1/4 = 3/4 P(Rr or RR) = 2/4 + 1/4 = 3/4
P(EP(E11 or E or E22) = P(E) = P(E11) + P(E) + P(E22))
Using Probability in Genetic Analysis
3. Multiplication Rule of Probability – used in an “and” situation
Eg. P(wrinkled, yellow) from cross RrYy x RrYy Eg. P(wrinkled, yellow) from cross RrYy x RrYy
P(rr and Y_) = 1/4 x 3/4 = 3/16 P(rr and Y_) = 1/4 x 3/4 = 3/16
P(EP(E11 and E and E22) = P(E) = P(E11) X P(E) X P(E22))
Using Probability in Genetic Analysis
4. Conditional Probability: Calculating the probability that each individual has a particular genotype
INTRODUCTION TO PROBLEM
Phenylketonuria (PKU) is a genetic disorder that is characterized by an inability of the body to utilize the essential amino acid, phenylalanine.
PROBLEM
Jack and Jill Jack and Jill do notdo not have PKU, have PKU, however however eacheach has a sibling with the has a sibling with the disease. What is the probability that disease. What is the probability that Jack and Jill will have a child with Jack and Jill will have a child with PKU?PKU?
What is the probability they will not What is the probability they will not have a child with PKU?have a child with PKU?
PROBLEM
What is the probability they will What is the probability they will notnot
have a child with PKU?have a child with PKU?
Using Probability in Genetic Analysis
5. Ordered Events: use Multiplication Rule
For Jack and Jill, what is the probability that For Jack and Jill, what is the probability that the first child will have PKU, the second child the first child will have PKU, the second child will not have PKU and the third child will have will not have PKU and the third child will have PKU?PKU?
Using Probability in Genetic Analysis
6. Binomial Rule of Probability Out of 3 children born to Jack and Jill,
what is the probability that 2 will have PKU?
The End