1 Mendelian Mendelian Inherita Inherita nce nce Ch. 11 Outline – Mendelian Ch. 11 Outline – Mendelian Inheritance Inheritance Blending Inheritance Blending Inheritance Monohybrid Cross Monohybrid Cross Law of Segregation Law of Segregation Modern Genetics Modern Genetics Genotype vs. Phenotype Genotype vs. Phenotype Punnett Square Punnett Square Dihybrid Cross Dihybrid Cross Law of Independent Assortment Law of Independent Assortment Human Genetic Disorders Human Genetic Disorders
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Mendelian Inheritance 1 Ch. 11 Outline – Mendelian Inheritance Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype vs.
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Law of Independent AssortmentLaw of Independent Assortment
Human Genetic DisordersHuman Genetic Disorders
2Mendelian IMendelian Inheritancenheritance
Gregor MendelGregor Mendel
Austrian monkAustrian monkStudied science and mathematics at Studied science and mathematics at University of ViennaUniversity of Vienna
Conducted breeding experiments with the Conducted breeding experiments with the garden pea garden pea Pisum sativumPisum sativum
Carefully gathered and documented Carefully gathered and documented mathematical data from his experimentsmathematical data from his experiments
Formulated fundamental laws of heredity in Formulated fundamental laws of heredity in early 1860searly 1860sHad no knowledge of cells or chromosomesHad no knowledge of cells or chromosomesDid not have a microscopeDid not have a microscope
3Gregor Mendel
4Fruit and Flower of the
Garden Pea
5Garden Pea TraitsStudied by
Mendel
6Mendelian IMendelian Inheritancenheritance
Blending InheritanceBlending Inheritance
Theories of inheritance in Mendel’s time:Theories of inheritance in Mendel’s time:
Based on blendingBased on blending
Parents of contrasting appearance produce Parents of contrasting appearance produce offspring of intermediate appearanceoffspring of intermediate appearance
Mendel’s findings were in contrast with thisMendel’s findings were in contrast with this
He formulated the particulate theory of He formulated the particulate theory of inheritanceinheritance
Inheritance involves reshuffling of genes from Inheritance involves reshuffling of genes from generation to generationgeneration to generation
7Mendelian IMendelian Inheritancenheritance
One-Trait InheritanceOne-Trait Inheritance
Mendel performed cross-breeding Mendel performed cross-breeding experimentsexperiments
Used “true-breeding” (homozygous) plantsUsed “true-breeding” (homozygous) plants
Chose varieties that differed in only one trait Chose varieties that differed in only one trait (monohybrid cross)(monohybrid cross)
Performed reciprocal crossesPerformed reciprocal crosses
Formulated the Law of SegregationFormulated the Law of Segregation
8Mendel’s Monohybrid Crosses:An Example
9Mendelian IMendelian Inheritancenheritance
Law of SegregationLaw of Segregation
Each individual has a pair of factors (alleles) Each individual has a pair of factors (alleles) for each traitfor each trait
The factors (alleles) segregate (separate) The factors (alleles) segregate (separate) during gamete (sperm & egg) formationduring gamete (sperm & egg) formation
Each gamete contains only one factor (allele) Each gamete contains only one factor (allele) from each pairfrom each pair
Fertilization gives the offspring two factors Fertilization gives the offspring two factors for each traitfor each trait
10Mendelian IMendelian Inheritancenheritance
Modern Genetics ViewModern Genetics View
Each trait in a pea plant is controlled by two Each trait in a pea plant is controlled by two alleles (alternate forms of a gene)alleles (alternate forms of a gene)
Dominant allele (capital letter) masks the Dominant allele (capital letter) masks the expression of the recessive allele (lower-expression of the recessive allele (lower-case)case)
Alleles occur on a homologous pair of Alleles occur on a homologous pair of chromosomes at a particular gene locuschromosomes at a particular gene locus
Heterozygous = different allelesHeterozygous = different alleles
11Homologous Chromosomes
12Mendelian IMendelian Inheritancenheritance
Genotype Versus PhenotypeGenotype Versus Phenotype
Genotype Genotype
Refers to the two alleles an individual has for Refers to the two alleles an individual has for a specific traita specific trait
If identical, genotype is homozygousIf identical, genotype is homozygous
If different, genotype is heterozygousIf different, genotype is heterozygous
Phenotype Phenotype
Refers to the physical appearance of the Refers to the physical appearance of the individualindividual
13Mendelian IMendelian Inheritancenheritance
Punnett SquarePunnett Square
Table listing all possible genotypes resulting Table listing all possible genotypes resulting from a crossfrom a cross
All possible sperm genotypes are lined up on All possible sperm genotypes are lined up on one sideone side
All possible egg genotypes are lined up on the All possible egg genotypes are lined up on the other sideother side
Every possible zygote genotypes are placed Every possible zygote genotypes are placed within the squareswithin the squares
14Punnett Square ShowingEarlobe Inheritance
Patterns
15Mendelian IMendelian Inheritancenheritance
Monohybrid TestcrossMonohybrid Testcross
Individuals with recessive phenotype always Individuals with recessive phenotype always have the homozygous recessive genotypehave the homozygous recessive genotype
However, Individuals with dominant However, Individuals with dominant phenotype have indeterminate genotypephenotype have indeterminate genotype
May be homozygous dominant, orMay be homozygous dominant, or
HeterozygousHeterozygous
Test cross determines genotype of individual Test cross determines genotype of individual having dominant phenotypehaving dominant phenotype
16One-Trait Test CrossUnknown is
Heterozygous
17One-Trait Test CrossUnknown is Homozygous
Dominant
18Mendelian IMendelian Inheritancenheritance
Two-Trait InheritanceTwo-Trait Inheritance
Dihybrid cross uses true-breeding plants Dihybrid cross uses true-breeding plants differing in two traitsdiffering in two traits
Observed phenotypes among FObserved phenotypes among F22 plants plants
Formulated Law of Independent AssortmentFormulated Law of Independent Assortment
The pair of factors for one trait segregate The pair of factors for one trait segregate independently of the factors for other traitsindependently of the factors for other traits
All possible combinations of factors can occur All possible combinations of factors can occur in the gametesin the gametes
19Two-Trait (Dihybrid) Cross
20Two-Trait Test Cross
21Mendelian IMendelian Inheritancenheritance
Human Genetic DisordersHuman Genetic Disorders
Autosome - Any chromosome other than a sex Autosome - Any chromosome other than a sex chromosomechromosome
Genetic disorders caused by genes on autosomes Genetic disorders caused by genes on autosomes are called autosomal disorders are called autosomal disorders Some genetic disorders are autosomal dominantSome genetic disorders are autosomal dominant An individual with AA has the disorderAn individual with AA has the disorder An individual with Aa has the disorderAn individual with Aa has the disorder An individual with aa does NOT have disorderAn individual with aa does NOT have disorder
Other genetic disorders are autosomal recessiveOther genetic disorders are autosomal recessive An individual with AA does NOT have disorderAn individual with AA does NOT have disorder An individual with Aa does NOT have disorder, but is a An individual with Aa does NOT have disorder, but is a
carriercarrier An individual with aa DOES have the disorderAn individual with aa DOES have the disorder
Progressive deterioration of psychomotor Progressive deterioration of psychomotor functionsfunctions
Cystic FibrosisCystic Fibrosis
Mucus in bronchial tubes and pancreatic Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscousducts is particularly thick and viscous
Phenylketonuria (PKU)Phenylketonuria (PKU)
Lack enzyme for normal metabolism of Lack enzyme for normal metabolism of phenylalaninephenylalanine
Tan or dark spots develop on skin and darken Tan or dark spots develop on skin and darken
Small, benign tumors may arise from fibrous Small, benign tumors may arise from fibrous nerve coveringsnerve coverings
Huntington DiseaseHuntington Disease
Neurological disorderNeurological disorder
Progressive degeneration of brain cellsProgressive degeneration of brain cells
Severe muscle spasmsSevere muscle spasms
Personality disordersPersonality disorders
27A Victim of Huntington Disease
28Huntington Disease:Normal and Diseased
Brain
29Mendelian IMendelian Inheritancenheritance
Incomplete DominanceIncomplete Dominance
Heterozygote has phenotype intermediate Heterozygote has phenotype intermediate between that of either homozygotebetween that of either homozygote
Homozygous red has red phenotypeHomozygous red has red phenotype
Homozygous white has white phenotypeHomozygous white has white phenotype
Heterozygote has pink (intermediate) Heterozygote has pink (intermediate) phenotypephenotype
Phenotype reveals genotype without test Phenotype reveals genotype without test crosscross
30Incomplete Dominance
31Mendelian IMendelian Inheritancenheritance
Multiple Allelic TraitsMultiple Allelic Traits
Some traits controlled by multiple allelesSome traits controlled by multiple alleles
The gene exists in several allelic forms (but each individual The gene exists in several allelic forms (but each individual only has two)only has two)
ABO blood typesABO blood types
The alleles:The alleles: IIAA = A antigen on red cells, anti-B antibody in plasma = A antigen on red cells, anti-B antibody in plasma IIBB = B antigen on red cells, anti-AB antibody in plasma = B antigen on red cells, anti-AB antibody in plasma II = Neither A nor B antigens, both antibodies = Neither A nor B antigens, both antibodies
A (actually AA or AO)A (actually AA or AO) IIAAIIAA or I or IAAiiB (actually BB or BO)B (actually BB or BO) IIBBIIBB or I or IBBii
ABAB IIAAIIBB
O (actually OO)O (actually OO) iiii
32Inheritance of Blood Type
33Mendelian IMendelian Inheritancenheritance
Polygenic InheritancePolygenic Inheritance
Occurs when a trait is governed by two or Occurs when a trait is governed by two or more genes having different allelesmore genes having different alleles
Each dominant allele has a quantitative effect Each dominant allele has a quantitative effect on the phenotypeon the phenotype
These effects are additiveThese effects are additive
Result in continuous variation of phenotypesResult in continuous variation of phenotypes
34Height in Human Beings
35Frequency Distributions in
Polygenic Inheritance
36Mendelian IMendelian Inheritancenheritance
TerminologyTerminology
PleiotropyPleiotropyA gene that affects more than one A gene that affects more than one characteristic of an individualcharacteristic of an individual
CodominanceCodominanceMore than one allele is fully expressedMore than one allele is fully expressedABO blood type (multiple allelic traits)ABO blood type (multiple allelic traits)
EpistasisEpistasisA gene at one locus interferes with the A gene at one locus interferes with the expression of a gene at a different locusexpression of a gene at a different locus
Human skin color (polygenic inheritance)Human skin color (polygenic inheritance)