Transmission of Genes From Generation to Generation Chapter 3

3.1 Heredity: How are Traits Inherited?  Why do we begin examining inheritance by discussing Gregor Mendel and pea plants?  Before Mendel there was no clear understanding of how traits were inherited and passed from one generation to the next  Mendel used experimental genetics to uncover the fundamental principles of inheritance

3.2 Mendel’s Experimental Design  Mendel’s experiments defined the ideal properties of an experimental organism:  It should have a number of different traits that can be studied  The plant should be self-fertilizing and have a flower that reduces accidental pollination  Offspring of self-fertilized plants should be fully fertile so more crosses can be made  hz7tCxjSE hz7tCxjSE

ANIMATION: Crossing garden pea plants To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/cross_pollination.html

Mendel’s Experiments in the Monastery Garden

Traits Selected for Study by Mendel

3.3 Crossing Pea Plants: Single Traits  Mendel’s initial crosses studied the inheritance of a single trait such as seed shape or seed color  When plants with smooth peas were crossed with plants having wrinkled peas, the offspring all produced smooth peas

3.3 Crossing Pea Plants: Single Traits P1:P1:Smooth X wrinkled F1:F1:Smooth Self-fertilize F 1 plants 5,474 Smooth 1,850 wrinkled F2:F2: Total peas in F 2 : 7,324 When the plants from these smooth seeds were crossed with each other, the offspring yielded 7,324 peas 5,474 were smooth and 1,850 were wrinkled

ANIMATION: Monohybrid cross To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/monohybrid_v2.html

INTERACTION: Test Cross To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

Mendel’s Terminology  P1 = parental generation  F1 = first filial (generation after parent generation) generation  F2 = second generation  So in this experiment  P1: smooth x wrinkled  F1: offspring all smooth  F2: offspring smooth (5,474) and wrinkled (1,850)

Mendel’s Conclusions  Only one of the parental traits was expressed in the F1 plants  Genetic factors can be hidden (unexpressed)  Despite identical appearance, P1 and F1 plants must have different genetic factors  F1 plants must carry hidden genetic factors  The trait not expressed in the F1 plants reappeared in 25% of the F2 plants  F1 plants must carry two factors, one from each parent. (these factors are now referred to as genes)  Traits were not blended as they passed though parents

Traits  Dominant Trait - Trait expressed in the F1 (heterozygous) condition  Recessive Trait - Trait repressed in the F1 but re- expressed in some members of the F2 generation  Phenotype - Observable properties of an organism  Genotype - The specific genetic constitution of an organism

Phenotype and Genotype P 1 : GenotypesSSss Meiosis PhenotypesSmoothwrinkled GametesSSss Fertilization F 1 : GenotypeSs PhenotypeSmooth X

Mendel’s Principle of Segregation  Pairs of factors (genes) separate from each other during gamete formation and exhibit dominant/recessive relationships  deWjUJBxGk deWjUJBxGk

Gene Pairs Segregate during Gamete Formation  Genes - Fundamental units of heredity  Segregation - Members of a gene pair separate from each other during gamete formation Ss Smooth S s S s F 1 cross Gamete formation by F 1 parents

Combinations of Gene Forms (Alleles)  Allele - One possible alternative form of a gene  Usually distinguished by its phenotypic effects  Homozygous - Having identical alleles for one or more genes  AA or aa  Heterozygous - Having two different alleles for one or more genes  Aa

ANIMATION: Genetic terms To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/genetic_terms_v2.html

Punnett Square Ss S s S Smooth S s S s s F 1 cross Gamete formation by F 1 parents Set up Punnett square GenotypePhenotype S s 1 SS 3/4 Smooth 2 Ss S sS Smooth Ss Smooth 1 ss 1/4 wrinkled s F 2 ratio Gamete combinations represent random fertilization ss wrinkled SS Smooth

3.4 The Principle of Independent Assortment  Members of one gene pair separate or segregate independently of other gene pairs  s s

Mendel’s Principle of Independent Assortment  Independent assortment - The random distribution of alleles into gametes during meiosis  Leads to formation of all possible combinations of gametes with equal probability in a cross between two individuals  ns/content/independentassortment.html ns/content/independentassortment.html

3.4 The Principle of Independent Assortment P 1 cross Smooth Yellow wrinkled green F1:F1: All Smooth Yellow F 1 x F 1 : Smooth Yellow F2:F2: 9/16 Smooth Yellow 3/16 Smooth green 3/16 wrinkled Yellow 1/16 wrinkled green x x

ANIMATION: Dihybrid cross To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

A Dihybrid Cross F1:F1: Smooth Yellow X F2:F2: Of all offspring Combined probabilities if Smooth 3/4 are Yellow ( 3/4 )( 3/4 ) = 9/16 Smooth Yellow 3/4 are Smooth 1/4 are green ( 3/4 )( 1/4 ) = 3/16 Smooth green and if wrinkled 1/4 are green ( 1/4 )( 1/4 ) = 1/16 wrinkled green 1/4 are wrinkled 3/4 are Yellow ( 1/4 )( 3/4 ) = 3/16 wrinkled Yellow

Punnett square Illustrates Independent Assortment in a Dihybrid Cross P 1 cross SSYY ssyy ssYY SSyy Smooth Yellow x wrinkled green wrinkled Yellow Smooth green Gamete formation SY sy sYSy Fertilization SsYy F 1 = Smooth Yellow F 1 cross SsYy P 1 cross x

Punnett square Illustrates Independent Assortment in a Dihybrid Cross SYSysYsy SY SSYY Smooth Yellow SSYy Smooth Yellow SsYY Smooth Yellow SsYy Smooth Yellow Sy SSYy Smooth Yellow SSyy Smooth green SsYy Smooth Yellow Ssyy Smooth green F2GeneratIonF2GeneratIon sY SsYY Smooth Yellow SsYy Smooth Yellow ssYY wrinkled Yellow ssYy wrinkled Yellow sy SsYy Smooth Yellow Ssyy Smooth green ssYy wrinkled Yellow ssyy wrinkle d green F 2 Genotypic ratios F 2 Phenotypic ratios SSYY 9/16 Smooth Yellow SSYy SsYY 4/16 SsYy 1/16 SSyy 3/16 Smooth green 2/16 Ssyy 1/16 ssYY 3/16 wrinkled Yellow 2/16ssYy 1/16ssyy1/16 wrinkled green SsYy F 1 cross SsYy x 1/16 2/16

Exploring Genetics: Evaluating Results: The Chi Square Test  A statistical test to determine whether the observed distribution of individuals in phenotypic categories is as predicted or occurs by chance X 2 = ∑ d 2 /E  Acceptable probability depends on the number of phenotypic classes df=n-1

Chi-Square Analysis of Mendel’s Data

Mendel’s Contribution  Mendel’s principle of segregation and principle of independent assortment are fundamental to our understanding of the science of heredity (genetics)

3.5 Meiosis Explains Mendel’s Results  Genes pairs (alleles) are located on chromosome pairs  The position occupied by a gene on a chromosome is referred to as a locus  The behavior of chromosomes in meiosis causes segregation and independent assortment of alleles

ANIMATION: Independent assortment To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/independent_assort.html

Genes, Chromosomes, and Meiosis

AaaAAaa Meiosis I BBb bbBB AAaa AAaa Metaphase II BBbb bbBB Gametes ABABababAbAbaBaB A b Segregation and Independent Assortment in Meiosis

3.6 Mendelian Inheritance in Humans  Inheritance of certain human traits is predictable based on Mendelian inheritance patterns

Aa AaAa GenotypePhenotype Aa 1 AA 3/4 normal 2 Aa A AA normal Aa normal 1 aa 1/4 albino a Aa normal aa albino Segregation of Albinism

AaDd ADADAdAdaDaDadad AADD Pigment Hearing AADd Pigment Hearing AaDD Pigment Hearing AaDd Pigment Hearing ADAD AADd Pigment Hearing AAdd Pigment Deaf AaDd Pigment Hearing Aadd Pigment Deaf AdAd AaDD Pigment Hearing AaDd Pigment Hearing aaDD Albino Hearing aaDd Albino Hearing aDaD AaDd Pigment Hearing Aadd Pigment Deaf aaDd Albino Hearing aadd Albino Deaf adad Independent Assortment of Two Traits Can be Followed

Pedigree  A diagram listing the members and ancestral relationships in a family  Used in the study of human heredity  Uses a standard form and symbols  Uses family history to show how a trait is inherited and estimate risk for family members  Provides genetic counseling for those at risk of having children with genetic disorders

Symbols Used in Pedigree Construction Male Aborted or stillborn offspring Female Deceased offspring Mating Mating between relatives (consanguineous) orUnaffected individual I Parents and children. Roman numerals symbolize generations. Arabic numbers symbolize birth order within generation (boy, girl, boy) orAffected individual II or 123 Proband; first case in family that was identified PP Monozygotic twins or Known heterozygotes Carrier of X-linked recessive trait Dizygotic twins Offspring of unknown sexInfertility

Numbering System used in Pedigrees  Each generation is identified by a Roman numeral  Each individual within a generation is identified by an Arabic number  Proband: The first affected family member who seeks medical attention for a genetic disorder

Following a Trait Through a Pedigree

ANIMATION: Pedigree diagrams To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/pedigree.html

3.8 Variations from Mendel  Alleles can interact in ways other than dominant/recessive  Incomplete dominance  Codominance  Multiple alleles  Different genes can interact  Epistasis

Incomplete Dominance  The expression of a phenotype that is intermediate to those of the parents.  An example is the inheritance of flower color in snapdragons:  R 1 R 1 (red) x R 2 R 2 (white) = R 1 R 2 (pink) x

INTERACTION: Incomplete dominance To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE file:///D:/Media/PowerPoint_Lect ures/chapter3/videos_animation s/snapdragon_crosses.html

Codominance  Full phenotypic expression of both members of a heterozygous gene pair  Blood Types - If a person is type AB this means that both the A allele and the B allele are equally expressed and are therefore codominant.  Roan fur in cattle. Many breeds of cattle are dominant for red hair or white hair

Multiple Alleles  Genes that have more than two alleles  The inheritance of the ABO blood types in humans  Rabbit coat color

Multiple Alleles A B AA B B A A B B A I Ai I A or I A i B I B or I B i A B B A A AB I A I B B O ii

Genes Can Interact to Produce Phenotypes  Epistasis - A form of gene interaction in which one gene masks or prevents expression of another gene.  Lab coat color  Albino gene is an epistatic gene. When the albino condition occurs, the genes that determine skin color are present, but not expressed.