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Observable Patterns of Observable Patterns of InheritanceInheritance
Earlobe Variation Earlobe Variation
Whether a person has attached or Whether a person has attached or detached earlobes depends on a single detached earlobes depends on a single genegene
Attached earlobes: two copies of the Attached earlobes: two copies of the recessive allele for this generecessive allele for this gene
Detached earlobes: either one or two Detached earlobes: either one or two copies of the dominant allelecopies of the dominant allele
Early Ideas about Heredity Early Ideas about Heredity
People knew that sperm and eggs People knew that sperm and eggs transmitted information about traitstransmitted information about traits
Blending theoryBlending theory Problem:Problem:
Would expect variation to disappearWould expect variation to disappear Variation in traits persistsVariation in traits persists
Gregor MendelGregor Mendel
Strong background Strong background in plant breeding and in plant breeding and mathematicsmathematics
Using pea plants, Using pea plants, found indirect but found indirect but observable evidence observable evidence of how parents of how parents transmit genes to transmit genes to offspringoffspring
Comments: GeneComments: Gene
MendelMendel never used the term, never used the term, genegene, , although he clearly made a distinction although he clearly made a distinction between, genotypes and phenotypes.between, genotypes and phenotypes.
The term, gene, was coined by The term, gene, was coined by Wilhelm Wilhelm Johannsen Johannsen (1909) based on the term, (1909) based on the term, PangenisisPangenisis which which Hugo de Vries Hugo de Vries (1889) (1889) used to describe Mendel’s concept of used to describe Mendel’s concept of inherited units that determine phenotypes.inherited units that determine phenotypes.
GenesGenes
Units of information about specific traitsUnits of information about specific traits
Passed from parents to offspringPassed from parents to offspring
Each has a specific location (locus) on a Each has a specific location (locus) on a chromosomechromosome
AllelesAlleles
Different molecular forms of a gene Different molecular forms of a gene
Arise by mutationArise by mutation
Dominant allele masks a recessive Dominant allele masks a recessive
allele that is paired with itallele that is paired with it
Allele CombinationsAllele Combinations
Homozygous Homozygous having two identical alleles at a locushaving two identical alleles at a locus AAAA or or aaaa
Heterozygous Heterozygous having two different alleles at a locushaving two different alleles at a locus AaAa
Genetic TermsGenetic Terms
A pair of homologous chromosomes
A gene locus
A pair of alleles
Three pairs of genes
Figure 11.4Page 179
Figure 11.4Page 179
Genotype & PhenotypeGenotype & Phenotype
Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries
Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits
Cannot always determine genotype by Cannot always determine genotype by observing phenotypeobserving phenotype
Parental generation P
mates to produce
First-generation offspring F1
mate to produce
Second-generation offspring F2
Monohybrid CrossesMonohybrid Crosses
Experimental intercross between Experimental intercross between
two two FF11 heterozygotes heterozygotes
AA X aa Aa (F1 monohybrids)
Aa X Aa ?
Mendel’s Mendel’s Monohybrid Monohybrid
Cross ResultsCross Results
787 tall 277 dwarf
651 long stem
207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
F2 plants showed dominant-to-recessive ratio that averaged 3:1
Figure 11.5Page 180
ProbabilityProbability
The chance that each outcome of a given The chance that each outcome of a given event will occur is proportional to the event will occur is proportional to the number of ways that event can be reachednumber of ways that event can be reached
Monohybrid Monohybrid CrossCross
IllustratedIllustrated
True-breedinghomozygous recessiveparent plant
True-breedinghomozygous dominantparent plant
An F1 plantself-fertilizesand producesgametes:
F1 PHENOTYPES
F2 PHENOTYPES
aa
Aa
AA
aaAa
Aa
Aa Aa
Aa Aa
Aa Aa
Aa Aa
Aa
Aa
AA
aa
A
A
A
A
a a
a
a
AA
Figure 11.7Page 181
Monohybrid Cross #1Monohybrid Cross #1
Long hair is dominant to short hair in Long hair is dominant to short hair in guinea pigs. Show the results of a cross guinea pigs. Show the results of a cross between a homozygous short haired male between a homozygous short haired male and a pure long haired female.and a pure long haired female.
Monohybrid Cross #1Monohybrid Cross #1
What do we know?What do we know? Both parents are homologous. Both parents are homologous. Short haired male hhShort haired male hh Long haired female HH (“H” gene is Long haired female HH (“H” gene is
dominant)dominant) hh x HHhh x HH Draw the Punnett SquareDraw the Punnett Square
#1 Punnett Square#1 Punnett Square
hh x HHhh x HH
HhHh HhHh
HhHh HhHh
All of the F1’s are hybrids, or heterogenous and they are long haired.
H
h
h
H Ova
sperm
zygotes
Meiosis2n -> n
Monohybrid #2Monohybrid #2
What is the probability that a cross What is the probability that a cross between two guinea pigs both between two guinea pigs both heterogeneous for long would produce a heterogeneous for long would produce a short haired guinea pig?short haired guinea pig?
Monohybrid #2Monohybrid #2
Hh x HhHh x Hh Draw the Punnett squareDraw the Punnett square
Complete the problem (p = ¼ or 25%)Complete the problem (p = ¼ or 25%)
H h
H
h
Monohybrid #3Monohybrid #3
In Holstein cattle the spotting of the coat is In Holstein cattle the spotting of the coat is due to a recessive allele while the solid due to a recessive allele while the solid colored coat is controlled by a dominant colored coat is controlled by a dominant allele. What types of offspring might be allele. What types of offspring might be produced by a cross between two spotted produced by a cross between two spotted animals?animals?
Monohybrid #3Monohybrid #3
Cross: spotted cow x spotted cowCross: spotted cow x spotted cow Cross: ss x ss Cross: ss x ss (where S = solid and s = spotted)(where S = solid and s = spotted)
Is it possible to have a solid calf?Is it possible to have a solid calf?
Monohybrid #4Monohybrid #4
In lemurs brown eyes are dominant over In lemurs brown eyes are dominant over blue eyes. If a heterozygous brown eyed blue eyes. If a heterozygous brown eyed female mates with a blue eyed male, what female mates with a blue eyed male, what would be the expected genotypic and would be the expected genotypic and phenotypic ratios of their offspring?phenotypic ratios of their offspring?
Monohybrid #4Monohybrid #4
Cross: Brown eyed heterozygous female and a Cross: Brown eyed heterozygous female and a blue eyed male (homozygous)blue eyed male (homozygous)
B = brown and b = blueB = brown and b = blue
Bb x bb = 2 Bb and 2 bbBb x bb = 2 Bb and 2 bb Genotypic ratioGenotypic ratio Bb:bb 1:1Bb:bb 1:1 Phenotypic ratioPhenotypic ratio Brown: blue 1:1Brown: blue 1:1
Monohybrid Problem SetMonohybrid Problem Set
Form cooperative groups of 2 to 4 andForm cooperative groups of 2 to 4 and Solve the problems in the Solve the problems in the Monohybrid Monohybrid
Problem Set.Problem Set. We’ll check the answers in class.We’ll check the answers in class.
Mendel’s Theory Mendel’s Theory of Segregationof Segregation
An individual inherits a unit of information An individual inherits a unit of information (allele) about a trait from each parent(allele) about a trait from each parent
During gamete formation, the alleles During gamete formation, the alleles segregate from each other segregate from each other
Test CrossTest Cross
Individual that shows dominant phenotype Individual that shows dominant phenotype is crossed with individual with recessive is crossed with individual with recessive phenotypephenotype
Examining offspring allows you to Examining offspring allows you to determine the genotype of the dominant determine the genotype of the dominant individualindividual
BB or Bb ?Both brownphenotypes
Punnett Squares of Punnett Squares of Test CrossesTest Crosses
Homozygous recessive
a a
A
a aa
Aa Aa
aa
Homozygous recessive
a a
A
A Aa
Aa Aa
Aa
Two phenotypes 1:1 All dominant phenotype
Dihybrid Cross Dihybrid Cross
Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different
versions of versions of twotwo traits traits
Dihybrid Cross: Dihybrid Cross: FF11 Results Results
AABB aabbx
AaBb
AB AB ab ab
TRUE-BREEDING PARENTS:
GAMETES:
F1 HYBRID OFFSPRING:
purple flowers, tall
white flowers,dwarf
All purple-flowered, tall
Figure 11.9 (1)Page 183
1/16aaBB
1/16aaBb
1/16aaBb
1/16Aabb
1/16Aabb
1/16AAbb
1/16AABB
1/16AABb
1/16AaBB
1/16AaBb
1/16AABb
1/16AaBb
1/16AaBB
1/16AaBb
1/16AaBb
1/4 AB 1/4 Ab 1/4 aB 1/4 ab
1/16aabb
1/4 AB
1/4 Ab
1/4 aB
1/4 ab
AaBb AaBbX
1/16 white-flowered, dwarf
3/16 white-flowered, tall
3/16 purple-flowered, dwarf
9/16 purple-flowered, tall
Dihybrid Cross: Dihybrid Cross: FF22 Results Results
Figure 11.9(2)Page 183
Dihybrid Problem #1Dihybrid Problem #1
A person is heterozygous for tongue-rolling and A person is heterozygous for tongue-rolling and homozygous recessive for freckles. This person homozygous recessive for freckles. This person marries an individual who is heterozygous for marries an individual who is heterozygous for both tongue-rolling and freckles. Show all the both tongue-rolling and freckles. Show all the possible genotypes for their children. possible genotypes for their children.
Tongue roller – Dominant Tongue roller – Dominant and and Non-tongue Non-tongue roller Recessiveroller Recessive
Freckles- Dominant Freckles- Dominant andand No Freckles RecessiveNo Freckles Recessive
Dihybrid Problem #1Dihybrid Problem #1
(Tongue roller – no-freckles) x (Tongue (Tongue roller – no-freckles) x (Tongue roller- freckles)roller- freckles)
T = tongue rolling dominantT = tongue rolling dominant tt = non-tongue rollingtt = non-tongue rolling F = freckles dominant ff = no frecklesF = freckles dominant ff = no freckles Ttff x TtFf (the cross)Ttff x TtFf (the cross) TtffTtff produces produces TfTf and and tftf gametes gametes TtFfTtFf produces produces TFTF, , TfTf,, tFtF, and , and tf tf gametesgametes
Dihybrid Problem #1Dihybrid Problem #1
Ttff x TtFf (symbolizes the cross)Ttff x TtFf (symbolizes the cross)
TTFf TTff TtfF Ttff
TtFf Ttff ttFf ttff
TF Tf tF tfOva
Tf
tf
sperm
zygotes
Dihybrid Problem #1Dihybrid Problem #1
Ttff x TtFf (symbolizes the cross)Ttff x TtFf (symbolizes the cross)
TTFf TTff TtfF Ttff
TtFf Ttff ttFf ttff
TF Tf tF tfOva
Tf
tf
sperm
zygotes
Roller-frecked
Roller-no freckles
Non-rollerfreckles
Non-rollerNo freckles
Phenotypic ratios: 3:3:1:1
Independent AssortmentIndependent Assortment
Mendel concluded that the two “units” for Mendel concluded that the two “units” for the first trait were to be assorted into the first trait were to be assorted into gametes independently of the two “units” gametes independently of the two “units” for the other traitfor the other trait
Members of each pair of homologous Members of each pair of homologous chromosomes are sorted into gametes at chromosomes are sorted into gametes at random during meiosis random during meiosis
Independent AssortmentIndependent Assortment
Metaphase I:
Metaphase II:
Gametes:
1/4 AB 1/4 ab 1/4 Ab 1/4 aB
A A A A
A A A A
AAAA
B B
B B
BB
B B
BBBB
a a a a
aa aa
aaaa
bb b b
bb b b
b b b b
OR
Dihybrid Problem SetDihybrid Problem Set
Form cooperative groups of 2 to 4 andForm cooperative groups of 2 to 4 and Solve the problems in the Solve the problems in the Dihybrid Dihybrid
Problem Set.Problem Set. We’ll check the answers in class.We’ll check the answers in class.
Tremendous VariationTremendous Variation
Number of genotypes possible in Number of genotypes possible in
offspring as a result of independent offspring as a result of independent
assortment and hybrid crossing is assortment and hybrid crossing is
22nn
((nn is the number of gene loci is the number of gene loci
at which the parents differ)at which the parents differ)
Impact of Mendel’s WorkImpact of Mendel’s Work
Mendel presented his results in 1865Mendel presented his results in 1865
Paper received little noticePaper received little notice
Mendel discontinued his experiments in Mendel discontinued his experiments in 18711871
Paper rediscovered in 1900 Paper rediscovered in 1900
Dominance Relations Dominance Relations
Complete dominance Complete dominance
Incomplete dominanceIncomplete dominance
CodominanceCodominance
Incomplete Incomplete DominanceDominance
XHomozygous parent
Homozygous parent
All F1 are heterozygous
X
F2 shows three phenotypes in 1:2:1 ratio
Incomplete Dominance
Figure 11.10Page 184
Codominance: ABO Blood Codominance: ABO Blood Types Types
Gene that controls ABO type codes for Gene that controls ABO type codes for enzyme that dictates structure of a enzyme that dictates structure of a glycolipid on blood cellsglycolipid on blood cells
Two alleles (Two alleles (IIAA and and IIBB) are codominant ) are codominant when pairedwhen paired
Third allele (Third allele (ii) is recessive to others) is recessive to others
ABO Blood Type:ABO Blood Type:Allele CombinationsAllele Combinations
Range of genotypes:
Blood types:
IA IA
IA i IA IB IB i
IB IB
ii
A AB B O
or or
Figure 11.11Page 184
ABO and TransfusionsABO and Transfusions
Recipient’s immune system will attack Recipient’s immune system will attack
blood cells that have an unfamiliar blood cells that have an unfamiliar
glycolipid on surfaceglycolipid on surface
Type O is universal donor because it has Type O is universal donor because it has
neither type A nor type B glycolipidneither type A nor type B glycolipid
Pleiotropy Pleiotropy
Alleles at a single locus may have effects Alleles at a single locus may have effects on two or more traitson two or more traits
Marfan syndrome - Mutation in gene for Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin system, lungs, eyes, and skin
Marfan SyndromeMarfan Syndrome
Campodactyly: Campodactyly: Unexpected Phenotypes Unexpected Phenotypes
Effect of allele varies:Effect of allele varies:
Bent fingers on both handsBent fingers on both hands
Bent fingers on one handBent fingers on one hand
No effectNo effect
Many factors affect gene expressionMany factors affect gene expression
Continuous VariationContinuous Variation
A more or less continuous range of small A more or less continuous range of small differences in a given trait among differences in a given trait among individualsindividuals
The greater the number of genes and The greater the number of genes and
environmental factors that affect a trait, the environmental factors that affect a trait, the
more continuous the variation in versions more continuous the variation in versions
of that traitof that trait
Human VariationHuman Variation
Some human traits occur as a few discrete Some human traits occur as a few discrete typestypes Attached or detached earlobes Attached or detached earlobes Many genetic disordersMany genetic disorders
Other traits show continuous variationOther traits show continuous variation HeightHeight WeightWeight Eye colorEye color IQIQ
Polygenic InheritancePolygenic Inheritance
Suppose height in humans is controlled by Suppose height in humans is controlled by three sets of genes each on a different three sets of genes each on a different chromosome (independently assorted). chromosome (independently assorted). Assume that each dominant allele Assume that each dominant allele contributes “1 unit of height” and a recessive contributes “1 unit of height” and a recessive allele produces only “½ unit of height”.allele produces only “½ unit of height”.
Two average heigth parents have the Two average heigth parents have the genotypes:genotypes:
AaBbCc x AaBbCcAaBbCc x AaBbCc
Polygenic InheritancePolygenic Inheritance
Each parent can produce 8 gametic gene Each parent can produce 8 gametic gene combinations:combinations:
ABC, ABc, AbC, aBC, Abc, aBc, abC, abcABC, ABc, AbC, aBC, Abc, aBc, abC, abc What size Punnett Square would we What size Punnett Square would we
need?need?
AABBCC
AABBCc
AABbCC
AaBBCC
AaBbCC
AaBBCc
AABbCc
AaBbCc
AABBCc
AABBcc
AABbCc
AaBBCc
AaBbCc
AaBBcc
AABbcc
AaBbcc
AABbCC
AABbCc
AAbbCC
AaBbCC
AabbCC
AaBbCc
AAbbCc
AabbCc
AaBBCC
AaBBCc
AaBbCC
aaBBCC
aaBbCC
aaBBCc
AaBbCc
aaBbCc
AaBbCC
AaBbCc
AabbCC
aaBbCC
aabbCC
aaBbCc
AaBbcc
aabbCc
AaBBCc
AaBBcc
AaBbCc
aaBBCc
aaBbCc
aaBBcc
AaBbcc
aaBbcc
AABbCc
AABbcc
AAbbCc
AaBbCc
AabbCc
AaBbcc
AAbbcc
Aabbcc
AaBbCc
AaBbcc
AabbCc
aaBbCc
aabbCc
aaBbcc
Aabbcc
aabbcc
ABC ABc Ab
CaBC
abC
aBc
Abc
abc
ABC
ABc
AbC
aBC
abC
`abc
Abc
aBc
5.5 units
5 units
4.5 units
4 units
3.5 units
6 units
3 units
ParentsAaBbCc4.5 units each
Roughly bell shaped
Polygenic inheritanceproduces a more or lesscontinuous distribution ofphenotypes. The more genesinvolved, the smoother thedistribution.
Describing Continuous Variation Describing Continuous Variation
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
(line of bell-shaped curve indicates continuous variation in population)
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
Temperature Effects Temperature Effects on Phenotype on Phenotype
Rabbit is homozygous for Rabbit is homozygous for an allele that specifies a an allele that specifies a heat-sensitive version of an heat-sensitive version of an enzyme in melanin-enzyme in melanin-producing pathwayproducing pathway
Melanin is produced in Melanin is produced in cooler areas of bodycooler areas of body
Figure 11.18Page 190
Environmental Effects on Plant Environmental Effects on Plant PhenotypePhenotype
Hydrangea macrophyllaHydrangea macrophylla Action of gene responsible for floral Action of gene responsible for floral
color is influenced by soil aciditycolor is influenced by soil acidity Flower color ranges from pink to blueFlower color ranges from pink to blue
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