How to study for this course
Genetics is a different biology class
Reading,attending lectures And
understanding the concept-not
memorizing
Do problem sets
Introduction to Genetics
What is Genetics?
Genetics research is focused on three areas.
Genetics has a long history.
Genetics is an experimental science.
How do geneticists choose experimental organisms?
Genetics is the study of heredity and
variation
Genetics is the
study of the
inheritance of
traits.
The gene is the
basic unit of
heredity.
Geneticists study
the inheritance,
structure,
function and
change of genes.
Genetics research is focused on three areas
Transmission Genetics
Molecular Genetics
Population/Evolutionary
Genetics
Transmission Genetics:
Mendelian Rules
Mutational Analysis
Controlled Breeding
Pedigree Analysis
Gene Interaction
Genetic Mapping
Chromosomal Mechanics
Developmental Analysis
Molecular Genetics:
DNA Structure
DNA Replication
Genetic Code
Transcription and Translation
Recombinant DNA
DNA Sequencing
Gene Cloning
Transgenic Plants and
Animals
Population/Evolutionary Genetics:
Measuring gene frequencies
Measuring gene changes
Estimating the rates of
change
Measuring the forces that
drive genetic change
Mutation,migration,
selection,genetic drift
History of Genetics
Before 1860
Lamarckian inheritance
Cell theory
1860 - 1900
Cell Cycle
1900 - 1944
Mendel
Chromosome theory
1944 - 1977
DNA
Genetic code
1977- today
Gene cloning
Eukaryotic gene structure
The Scientific Method
Genetics relies on the scientific method to
study genes and traits
Observation
Hypotheses
Testing
Genetics is an Experimental Science
Observation
Hypothesis
Prediction
Experiment
New Hypothesis
Information comes from
observation
Ideas are tested by
experimentation
Controlled experiments
generate reliable data
Model organisms are widely
used
Choosing an Experimental Organism
The organism should be small.
The organism should produce
many progeny.
The life cycle should be short.
The organism should have a small
genome.
The organism should be
developmentally complex.
Accumulated knowledge is
essential.
Mendelian Genetics
Who was Gregor Mendel?
What were Mendel’s experiments?
How did Mendel derive his rules?
How do geneticists diagram crosses?
What are the rules of probability geneticists use?
What can we learn from pedigree analysis?
Mendel performed simple crosses
Parent generation P1 X P2
First Filial generation F1
Second Filial generation F2
In each generation he recorded the phenotype of each
individual and the number with each phenotype,
Dominance,One allele controls the phenotype.
Dominant phenotype is given by two genotypes:
Homozygote and heterozygote,RR and Rr
Recessive phenotype is given by one phenotype:
Homozygote:rr
Mendel’s first observation,
Alleles show dominance
Mendel’s Rule of Segregation
Somatic cells have two alleles of each gene but gametes
have only one allele.
The alleles of each gene segregate during gamete
formation,
The principle of allele segregation is known as Mendel’s
first rule.
Parent = Rr
Gametes = 1/2 R 1/2 r
Conclusions from monohybrid crosses:
The F2 had a constant phenotypic ratio of 3:1
The F2 had a constant genotypic ratio of 1:2:1
Smooth Yellow 51 Rr Yy
wrinkled green X F1 backcross results
wrinkled green 52 rr yy
Smooth green 51 Rr yy
wrinkled Yellow 49 rr Yy
Parents
wrinkled green X Round Yellow
rr yy RR YY
F1 Round Yellow
Rr Yy
F2?
Mendel’s dihybrid cross,Do the rules of
monohybrid crosses hold for dihybrid crosses?
Are multiple traits
inherited as a unit,or
are they inherited
independently?
Test,a dihybrid
cross.
Smooth Yellow 315 9/16
F2 Phenotypes
wrinkled green 32 1/16
Smooth green 108 3/16
wrinkled Yellow 101 3/16
Observed Ratio
Mendel’s second rule,Independent
Assortment.
Mendel used the rule of segregation to derive a new
hypothesis,
The alleles of the two genes segregate
independently,producing four equally frequent
gamete genotypes.
Random gamete fusion produces 4 X 4 = 16 offspring
classes,some with the same genotype.
Dominance produces four phenotypes in a 9:3:3:1
ratio.
Rules of Probability
Sum rule,The probability that either of two events will
occur is the sum of their separate probabilities.
p(A or B) = p(A) + p(B)
Product rule,The probability that two events will both
occur simultaneously is the product of their separate
probabilities.
p(A and B) = p(A) X p(B).
Problems
If you flip a coin 5 times,what is the possibility that
all five times you get the face side?
A dice has six sides with numbers 1-6,what is the
possibility that you get a number no smaller than 5?
If you roll the dice 3 times,what is the possibility
you get all of them no smaller than 5?
In statistics,there are two significance levels that
people often adopt,One at 95% (5%) and another
99% (1%),Anything beyond the adopted number is
to be rejected at that particular threshhold
(significance) level.
In the previous example,the possibility of getting
all 5 face side is 1/32,So at 95% significance level,
the possibility of the event happening is rejected,
However,at 99% significance level,it cannot be
rejected,
Take-home question
Two isolated islands have different family planning
policies,In island A,one couple can have only one
child,In island B,couples with one girl are allowed to
have a second child,but couples with one boy are not
allowed to do so,Does this policy difference affect the
male-female ratio of the future generation in these two
islands?
Crosses can be illustrated using a branching diagram
2.7
Problem:
In a cross
Rr Yy Tt X rr Yy tt
What is the probability that the first offspring will have a
rr YY tt genotype?
What is the probability that the first offspring will have a
R Y t phenotype?
Answer:
Rr x rr = 1/2 Rr,1/2 rr = 1/2 round 1/2 wrinkled
Yy x Yy = 1/4 YY,1/2Yy,1/4 yy = 3/4 yellow,1/4 green
Tt x tt = 1/2 Tt and 1/2 tt = 1/2 tall,1/2 short
Each event is independent,so the product rule is used
for combinations.
Pedigree Analysis
Mendel’s laws allow us to analyze the genetic
information in family records (pedigrees).
From this we can determine the nature of alleles
controlling traits,From this we can:
deduce whether the trait is dominant or recessive
deduce whether the trait is sex linked
deduce the genotypes of members of the family,
predict the phenotypes of future offspring.
deduce the genotypes of parents from their offspring
phenotypes.
In a pedigree,each individual
is represented by a symbol.
The shape,color,and
location of the symbol carry
information about the sex and
phenotype of the individual.
2.11
Is this a
dominant or
recessive trait?
Is this a dominant or recessive pattern of inheritance?
What is the nature of the allele?
What are the genotypes of each individual?
What is the probability that a cross between III1 and III2
will produce an individual with the trait?
I
II
III
The allele is recessive.
Some cannot be determined exactly.
Probability of homozygous offspring = 2/3 X 2/3 X 1/4 = 1/9
Aa Aa Aa Aa
A- A- aa Aa Aa A- A- aa
A- A- A- A- aa A- aa
Genetics is a different biology class
Reading,attending lectures And
understanding the concept-not
memorizing
Do problem sets
Introduction to Genetics
What is Genetics?
Genetics research is focused on three areas.
Genetics has a long history.
Genetics is an experimental science.
How do geneticists choose experimental organisms?
Genetics is the study of heredity and
variation
Genetics is the
study of the
inheritance of
traits.
The gene is the
basic unit of
heredity.
Geneticists study
the inheritance,
structure,
function and
change of genes.
Genetics research is focused on three areas
Transmission Genetics
Molecular Genetics
Population/Evolutionary
Genetics
Transmission Genetics:
Mendelian Rules
Mutational Analysis
Controlled Breeding
Pedigree Analysis
Gene Interaction
Genetic Mapping
Chromosomal Mechanics
Developmental Analysis
Molecular Genetics:
DNA Structure
DNA Replication
Genetic Code
Transcription and Translation
Recombinant DNA
DNA Sequencing
Gene Cloning
Transgenic Plants and
Animals
Population/Evolutionary Genetics:
Measuring gene frequencies
Measuring gene changes
Estimating the rates of
change
Measuring the forces that
drive genetic change
Mutation,migration,
selection,genetic drift
History of Genetics
Before 1860
Lamarckian inheritance
Cell theory
1860 - 1900
Cell Cycle
1900 - 1944
Mendel
Chromosome theory
1944 - 1977
DNA
Genetic code
1977- today
Gene cloning
Eukaryotic gene structure
The Scientific Method
Genetics relies on the scientific method to
study genes and traits
Observation
Hypotheses
Testing
Genetics is an Experimental Science
Observation
Hypothesis
Prediction
Experiment
New Hypothesis
Information comes from
observation
Ideas are tested by
experimentation
Controlled experiments
generate reliable data
Model organisms are widely
used
Choosing an Experimental Organism
The organism should be small.
The organism should produce
many progeny.
The life cycle should be short.
The organism should have a small
genome.
The organism should be
developmentally complex.
Accumulated knowledge is
essential.
Mendelian Genetics
Who was Gregor Mendel?
What were Mendel’s experiments?
How did Mendel derive his rules?
How do geneticists diagram crosses?
What are the rules of probability geneticists use?
What can we learn from pedigree analysis?
Mendel performed simple crosses
Parent generation P1 X P2
First Filial generation F1
Second Filial generation F2
In each generation he recorded the phenotype of each
individual and the number with each phenotype,
Dominance,One allele controls the phenotype.
Dominant phenotype is given by two genotypes:
Homozygote and heterozygote,RR and Rr
Recessive phenotype is given by one phenotype:
Homozygote:rr
Mendel’s first observation,
Alleles show dominance
Mendel’s Rule of Segregation
Somatic cells have two alleles of each gene but gametes
have only one allele.
The alleles of each gene segregate during gamete
formation,
The principle of allele segregation is known as Mendel’s
first rule.
Parent = Rr
Gametes = 1/2 R 1/2 r
Conclusions from monohybrid crosses:
The F2 had a constant phenotypic ratio of 3:1
The F2 had a constant genotypic ratio of 1:2:1
Smooth Yellow 51 Rr Yy
wrinkled green X F1 backcross results
wrinkled green 52 rr yy
Smooth green 51 Rr yy
wrinkled Yellow 49 rr Yy
Parents
wrinkled green X Round Yellow
rr yy RR YY
F1 Round Yellow
Rr Yy
F2?
Mendel’s dihybrid cross,Do the rules of
monohybrid crosses hold for dihybrid crosses?
Are multiple traits
inherited as a unit,or
are they inherited
independently?
Test,a dihybrid
cross.
Smooth Yellow 315 9/16
F2 Phenotypes
wrinkled green 32 1/16
Smooth green 108 3/16
wrinkled Yellow 101 3/16
Observed Ratio
Mendel’s second rule,Independent
Assortment.
Mendel used the rule of segregation to derive a new
hypothesis,
The alleles of the two genes segregate
independently,producing four equally frequent
gamete genotypes.
Random gamete fusion produces 4 X 4 = 16 offspring
classes,some with the same genotype.
Dominance produces four phenotypes in a 9:3:3:1
ratio.
Rules of Probability
Sum rule,The probability that either of two events will
occur is the sum of their separate probabilities.
p(A or B) = p(A) + p(B)
Product rule,The probability that two events will both
occur simultaneously is the product of their separate
probabilities.
p(A and B) = p(A) X p(B).
Problems
If you flip a coin 5 times,what is the possibility that
all five times you get the face side?
A dice has six sides with numbers 1-6,what is the
possibility that you get a number no smaller than 5?
If you roll the dice 3 times,what is the possibility
you get all of them no smaller than 5?
In statistics,there are two significance levels that
people often adopt,One at 95% (5%) and another
99% (1%),Anything beyond the adopted number is
to be rejected at that particular threshhold
(significance) level.
In the previous example,the possibility of getting
all 5 face side is 1/32,So at 95% significance level,
the possibility of the event happening is rejected,
However,at 99% significance level,it cannot be
rejected,
Take-home question
Two isolated islands have different family planning
policies,In island A,one couple can have only one
child,In island B,couples with one girl are allowed to
have a second child,but couples with one boy are not
allowed to do so,Does this policy difference affect the
male-female ratio of the future generation in these two
islands?
Crosses can be illustrated using a branching diagram
2.7
Problem:
In a cross
Rr Yy Tt X rr Yy tt
What is the probability that the first offspring will have a
rr YY tt genotype?
What is the probability that the first offspring will have a
R Y t phenotype?
Answer:
Rr x rr = 1/2 Rr,1/2 rr = 1/2 round 1/2 wrinkled
Yy x Yy = 1/4 YY,1/2Yy,1/4 yy = 3/4 yellow,1/4 green
Tt x tt = 1/2 Tt and 1/2 tt = 1/2 tall,1/2 short
Each event is independent,so the product rule is used
for combinations.
Pedigree Analysis
Mendel’s laws allow us to analyze the genetic
information in family records (pedigrees).
From this we can determine the nature of alleles
controlling traits,From this we can:
deduce whether the trait is dominant or recessive
deduce whether the trait is sex linked
deduce the genotypes of members of the family,
predict the phenotypes of future offspring.
deduce the genotypes of parents from their offspring
phenotypes.
In a pedigree,each individual
is represented by a symbol.
The shape,color,and
location of the symbol carry
information about the sex and
phenotype of the individual.
2.11
Is this a
dominant or
recessive trait?
Is this a dominant or recessive pattern of inheritance?
What is the nature of the allele?
What are the genotypes of each individual?
What is the probability that a cross between III1 and III2
will produce an individual with the trait?
I
II
III
The allele is recessive.
Some cannot be determined exactly.
Probability of homozygous offspring = 2/3 X 2/3 X 1/4 = 1/9
Aa Aa Aa Aa
A- A- aa Aa Aa A- A- aa
A- A- A- A- aa A- aa
