Transcript Rule of multiplication

Ch. 14 Mendelian Genetics
• Gregor Mendel (1822-1884)
– Determined particulate nature of inheritance –
parents transmit discrete inheritable factors
(genes) that remain as separate factors from
one generation to the next.
• Mendel liked peas. Peas are good.
• Peas have several characters with two
distinct forms (traits)
– flower color is purple or white
– Seed shape is round or wrinkled
• Mendel did separate experiments looking
at seven individual pea characters. He
crossed two plants, each true breeding for
alternate traits of a character (example:
purple flowers and white flowers). This
was the parental generation (p1).
• Each time he found the offspring all had
the same trait. This was the first filial (f1)
generation.
• He then crossed the f1 generation with
itself to get the f2 generation.
• He found that the other parental trait came
back! And…… the two traits were always
in a 3:1 ratio.
• This happened for all 7 characters he
studied.
• Soooooo…… getting back to flower
color…
• Soooooo…… getting back to flower
color…
– Since the white color came back, the plants in
the f1 generation must have still had a
discrete factor for white color, but it was
hidden. He called that factor recessive and
the other dominant.
• Soooooo…… getting back to flower
color…
– Since the white color came back, the plants in
the f1 generation must have still had a
discrete factor for white color, but it was
hidden. He called that factor recessive and
the other dominant.
– Each plant must have 2 factors for each
character, one from male parent, one from
female parent.
• Soooooo…… getting back to flower color…
– Since the white color came back, the plants in the f1
generation must have still had a discrete factor for
white color, but it was hidden. He called that factor
recessive and the other dominant.
– Each plant must have 2 factors for each character,
one from male parent, one from female parent.
– These factors must segregate during gamete
formation, leaving the possibility for factors to
randomly combine during fertilization
• Soooooo…… getting back to flower color…
– Since the white color came back, the plants in the f1
generation must have still had a discrete factor for
white color, but it was hidden. He called that factor
recessive and the other dominant.
– Each plant must have 2 factors for each character,
one from male parent, one from female parent.
– These factors must segregate during gamete
formation, leaving the possibility for factors to
randomly combine during fertilization
– Today we know these factors to be genes and the
alternate forms alleles.
• Mendel’s Law of Segregation
• Mendel’s Law of Segregation
– Allele pairs segregate during gamete
formation and the paired condition is restored
by the random fusion of gametes at
fertilization.
• Outcomes of crosses, in genotypic and
phenotypic ratios, may be predicted with
Punnett squares.
• Test crosses can determine unknown
genotypes
• Mendel’s second group of experiments
were like the first except he looked at the
inheritance of two traits together.
• Mendel’s second group of experiments
were like the first except he looked at the
inheritance of two traits together.
– Were characters for different traits inherited
together or independently?? If so, the f2
generation would have the same 3:1
phenotype ratio.
• Mendel’s Law of Independent
Assortment resulted from his dihybrid
crosses:
• Mendel’s Law of Independent
Assortment resulted from his dihybrid
crosses:
– Each allele pair segregates independently of
other gene pairs during gamete formation.
• Using the laws of probability to predict
mating outcomes.
• Using the laws of probability to predict
mating outcomes.
– Probability scale:
• Using the laws of probability to predict
mating outcomes.
– Probability scale:
– Probabilities of all possible outcomes =
• Using the laws of probability to predict
mating outcomes.
– Probability scale:
– Probabilities of all possible outcomes =
– Rule of multiplication
• Using the laws of probability to predict
mating outcomes.
– Probability scale:
– Probabilities of all possible outcomes =
– Rule of multiplication
• Used to determine the chance that two or more
independent events will occur together.
• Using the laws of probability to predict
mating outcomes.
– Probability scale:
– Probabilities of all possible outcomes =
– Rule of multiplication
• Used to determine the chance that two or more
independent events will occur together.
• Determined by multiplying the probability of each
independent event
– Rule of addition
– Rule of addition
• The probability of an event that can occur in two or
more different ways is the sum of the separate
probabilities
• Other forms of Inheritance
• Other forms of Inheritance
– Incomplete dominance
• Other forms of Inheritance
– Incomplete dominance
• Neither allele is fully dominant
• Other forms of Inheritance
– Incomplete dominance
• Neither allele is fully dominant
• Heterozygote phenotype is intermediate
• Other forms of Inheritance
– Incomplete dominance
• Neither allele is fully dominant
• Heterozygote phenotype is intermediate
• Mendel’s particulate nature of inheritance still
applies.
– Codominance
– Codominance
• Both alleles are fully expressed in the phenotype
– Codominance
• Both alleles are fully expressed in the phenotype
– Example: MN blood groups, roan coat color in horses
– Multiple alleles
– Multiple alleles
• When there are more than two alternate forms of a
gene.
– Multiple alleles
• When there are more than two alternate forms of a
gene.
• Each individual carries only two
– Multiple alleles
• When there are more than two alternate forms of a
gene.
• Each individual carries only two
– Example ABO blood group
– Epistasis
– Epistasis
• A gene at one locus alters the phenotypic
expression of a gene at another locus
– Epistasis
• A gene at one locus alters the phenotypic
expression of a gene at another locus
– Example coat color and melanin deposition in mice
– Epistasis
• A gene at one locus alters the phenotypic
expression of a gene at another locus
– Example coat color and melanin deposition in mice
– Example labrador retriever coat color
– Polygenic Inheritance
– Polygenic Inheritance
• Quantitative characters with a continuum of
expression
– Polygenic Inheritance
• Quantitative characters with a continuum of
expression
• Characters controlled by more than one gene
– Polygenic Inheritance
• Quantitative characters with a continuum of
expression
• Characters controlled by more than one gene
• Often are “multifactorial” and have a broad “Norm
of reaction”
– Polygenic Inheritance
• Quantitative characters with a continuum of
expression
• Characters controlled by more than one gene
• Often are “multifactorial” and have a broad “Norm
of reaction”
– Example : skin color