Mendelian Inheritance Chapter 11. Mendelian Inheritance 2Outline Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype

Mendelian Inheritance

Chapter 11

2Mendelian IMendelian Inheritancenheritance

OutlineOutline

Blending InheritanceBlending Inheritance

Monohybrid CrossMonohybrid Cross

Law of SegregationLaw of Segregation

Modern GeneticsModern Genetics

Genotype vs. PhenotypeGenotype vs. Phenotype

Punnett SquarePunnett Square

Dihybrid CrossDihybrid Cross

Law of Independent AssortmentLaw of Independent Assortment

Human Genetic DisordersHuman Genetic Disorders


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

4Gregor Mendel

5Fruit and Flower of the

Garden Pea

6Garden Pea TraitsStudied by

Mendel



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


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

Parental generation = PParental generation = P

First filial generation offspring = FFirst filial generation offspring = F11

Second filial generation offspring = FSecond filial generation offspring = F22

Formulated the Law of SegregationFormulated the Law of Segregation

9Mendel’s Monohybrid Crosses:An Example



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


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

Homozygous = identical allelesHomozygous = identical alleles

Heterozygous = different allelesHeterozygous = different alleles

12Homologous Chromosomes


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



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

15Punnett Square ShowingEarlobe Inheritance

Patterns


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

17One-Trait Test CrossUnknown is

Heterozygous

18One-Trait Test CrossUnknown is Homozygous

Dominant


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

20Two-Trait (Dihybrid) Cross

21Two-Trait Test Cross



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

23Autosomal Recessive Pedigree Chart

24Autosomal Dominant Pedigree Chart


Autosomal Recessive DisordersAutosomal Recessive Disorders

Tay-Sachs DiseaseTay-Sachs Disease

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

26Cystic Fibrosis Therapy


Autosomal Dominant DisordersAutosomal Dominant Disorders

NeurofibromatosisNeurofibromatosis

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

28A Victim of Huntington Disease

29Huntington Disease:Normal and Diseased

Brain


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

31Incomplete Dominance


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

PhenotypePhenotype(Blood Type)(Blood Type) GenotypeGenotype

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

33Inheritance of Blood Type


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

35Height in Human Beings

36Frequency Distributions in

Polygenic Inheritance


TerminologyTerminology

PleiotropyPleiotropyA gene that affects more than one A gene that affects more than one characteristic of an individualcharacteristic of an individual

Sickle-cell (incomplete dominance)Sickle-cell (incomplete dominance)

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)

38Environment and Phenotype:

Himalayan Rabbits


ReviewReview


Monohybrid CrossMonohybrid Cross


Modern GeneticsModern Genetics

Genotype vs. PhenotypeGenotype vs. Phenotype


Dihybrid CrossDihybrid Cross

Law of Independent AssortmentLaw of Independent Assortment


Mendelian Inheritance

Ending Slide Chapter 11

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Mendelian Inheritance Chapter 11. Mendelian Inheritance 2Outline Blending Inheritance Monohybrid Cross Law of Segregation Modern Genetics Genotype