Patterns of InheritancePatterns of Inheritance

Chapter 10Chapter 10

Blending Hypothesis of Blending Hypothesis of InheritanceInheritance TraitTrait

A variation of a particular A variation of a particular characteristiccharacteristic

Blending hypothesis (1800s)Blending hypothesis (1800s) Early explanation of how offspring Early explanation of how offspring

inherit trait from both parentsinherit trait from both parents Example: if a red flower plant Example: if a red flower plant

crossed with a yellow flower, the crossed with a yellow flower, the offspring would be orangeoffspring would be orange

Later discardedLater discarded

Gregor MendelGregor Mendel

Austrian monkAustrian monk Father of Father of GeneticsGenetics (study of (study of

heredity)heredity) Said parents pass on to their Said parents pass on to their

offspring separate and distinct genesoffspring separate and distinct genes Studied 7 characteristics in pea Studied 7 characteristics in pea

plantsplants

True breeding plantsTrue breeding plants A true plant will show the same physical A true plant will show the same physical

appearance generation after generation appearance generation after generation after after self-fertilizationself-fertilization

Cross fertilizationCross fertilization The sperm from the pollen of one true The sperm from the pollen of one true

flower fertilizes the eggs in the flower of flower fertilizes the eggs in the flower of a different planta different plant

Mendel's ExperimentsMendel's Experiments

Cross-fertilizedCross-fertilized 2 true-breeding 2 true-breeding plants each with contrasting traits plants each with contrasting traits (i.e. white and purple flowers)(i.e. white and purple flowers)

What color of flowers do you think What color of flowers do you think the offspring plants were? the offspring plants were?

Principle of SegregationPrinciple of Segregation P generationP generation

Parental plants (purebred and true Parental plants (purebred and true breeding) breeding)

FF1 1 generationgeneration ( F for filial “son”) ( F for filial “son”) Hybrid offspringHybrid offspring HybridsHybrids

The offspring of 2 different true-breeding The offspring of 2 different true-breeding varietiesvarieties

FF2 2 generationgeneration When F1 self-fertilize or fertilize each When F1 self-fertilize or fertilize each

otherother

Monohybrid CrossMonohybrid Cross

Monohybrid crossMonohybrid cross Cross fertilization in which only one Cross fertilization in which only one

physicalphysical characteristic is characteristic is consideredconsidered

In Mendel's cross, all F1 were In Mendel's cross, all F1 were purple but ¼ of F2 were whitepurple but ¼ of F2 were white

Gene Hypotheses #1Gene Hypotheses #1• There are alternative forms of There are alternative forms of

genes which determine physical genes which determine physical appearancesappearances

AlleleAllele is the term is the term Example: Flower color can be white Example: Flower color can be white

or purpleor purple

Gene Hypotheses #2Gene Hypotheses #2

• For each characteristic, an For each characteristic, an organism has 2 alleles for genes organism has 2 alleles for genes controlling the physical controlling the physical appearances (one from each appearances (one from each parent)parent)

• If 2 alleles are the same= If 2 alleles are the same= homozygoushomozygous• If 2 alleles are different =If 2 alleles are different =heterozygousheterozygous

Gene Hypotheses #3Gene Hypotheses #3 Dominant allelesDominant alleles determine the physical determine the physical

appearance in a heterozygous individual.appearance in a heterozygous individual.

Recessive alleleRecessive allele is the other allele that is the other allele that does not affect the physical appearancedoes not affect the physical appearance

Capital letter represents Capital letter represents dominant alleledominant allele : P: P Lower case letter Lower case letter represents represents recessive allelerecessive allele: p: p

PhenotypePhenotype is the physical is the physical appearanceappearance purplepurple purplepurple whitewhite

GenotypeGenotype is the genetic makeup is the genetic makeup Possible genotype are PP, Pp, pp.Possible genotype are PP, Pp, pp.

Gene Hypotheses #4Gene Hypotheses #4

The two alleles for a character The two alleles for a character segregate (separate) during meiosis segregate (separate) during meiosis so that each gamete carries only one so that each gamete carries only one allele for each character, known as allele for each character, known as principle of segregation. principle of segregation.

Punnett SquarePunnett Square

The alignment of combination of The alignment of combination of gametes to form zygotes with pairs of gametes to form zygotes with pairs of alleles is randomalleles is random Like tossing a coin.Like tossing a coin.

Punnett SquarePunnett Square is a diagram that shows is a diagram that shows all possible outcomes of a genetic cross.all possible outcomes of a genetic cross. Used to predict probabilities of outcomes if Used to predict probabilities of outcomes if

you know the genotypes of the parentsyou know the genotypes of the parents

The TestcrossThe Testcross

Breeds an individual of unknown Breeds an individual of unknown genotype, but dominant phenotype genotype, but dominant phenotype (purple) (purple) withwith a homozygous a homozygous recessive individual (white)recessive individual (white) Appearance of F1 will reveal the Appearance of F1 will reveal the

genotype of the mystery parentgenotype of the mystery parent If white flowers are produced, the If white flowers are produced, the

unknown parent must be heterozygous unknown parent must be heterozygous (Pp) and have a recessive trait(Pp) and have a recessive trait

Intermediate DominanceIntermediate Dominance Heterozygotes have a phenotype Heterozygotes have a phenotype

intermediateintermediate between the phenotypes between the phenotypes of the two homozygote of the two homozygote This is referred to as INCOMPLETE This is referred to as INCOMPLETE

DOMINANCEDOMINANCE Rules: (example: snapdragon flowers)Rules: (example: snapdragon flowers)

Capital/lower case letters not usedCapital/lower case letters not used Instead, a C for “color” is paired with a Instead, a C for “color” is paired with a

superscript R for “red” and W for “white”superscript R for “red” and W for “white” CCR R CCRR is red and Cis red and CW W CCW W is whiteis white CCR R CCW W is pinkis pink

There is a breed of chicken called Andalusians, black and white parents produce F1 hybrid offspring, called

"blues," with grayish-blue feathers.

Because neither the black nor white allele is dominant, capital and lowercase letters are not used to represent them.

Instead, a C for "color" is paired with a superscript B for "black" or W for "white" to represent the two alleles.

A heterozygote chicken has one of each allele, CBCW, and is grayish-blue in color

Although the F1 phenotypes are

intermediate, this inheritance pattern does not support the blending hypothesis.

This is because the parent phenotypes can reappear in the F2

generation.

Multiple allelesMultiple alleles

Heterozygote express the distinct traits Heterozygote express the distinct traits of of bothboth alleles alleles

Example: Human blood systemExample: Human blood system A, B, AB, or oA, B, AB, or o The letters are The letters are antigensantigens found on the found on the

surface of red blood cellssurface of red blood cells Red blood cells may be coated with Red blood cells may be coated with

one protein (A), the other (B), both one protein (A), the other (B), both (AB), or neither (O)(AB), or neither (O)

There are six possible genotype There are six possible genotype combinationscombinations

ABO blood type is a genetic example of multiple alleles.

There are three alleles in the gene pool for ABO blood type.

IA

IB

i

IA codes for protein A

IB codes for protein B

i codes for neither protein A nor protein B.

Within this multiple allele pool the gene interactions illustrate both simple dominance as well as co-dominance.

Remember each individual has only two alleles for each trait even if there are multiple alleles in the gene pool.

IAIA

both code for A type blood

IAi

PhenotypePhenotype GenotypeGenotype Protein on Protein on RBC RBC (antigen)(antigen)

Antibodies Antibodies in the in the blood blood plasmaplasma

Type AType A IIAA I IAA and and

IIAA i iAA bb

Type BType B IIBB I IBB and and

IIBB i iBB aa

Type ABType AB IIAA I IBB A and BA and B --------------------------

Type OType O iiii ---------------------- a and ba and b

ABO Blood SystemABO Blood System

AntibodiesAntibodies (proteins) also found in the (proteins) also found in the blood serum that attacks foreign blood serum that attacks foreign antigensantigens Blood A has antibody Anti-BBlood A has antibody Anti-B Blood B has antibody Anti-ABlood B has antibody Anti-A Blood AB has no antibodyBlood AB has no antibody Blood O has Antibody Anti A and BBlood O has Antibody Anti A and B

Blood O is the universal donorBlood O is the universal donor Blood AB can receive any blood typeBlood AB can receive any blood type

Rh FactorRh Factor

Rh positive (Rh +) has protein in Rh positive (Rh +) has protein in bloodblood

Rh negative (Rh -) has no protein in Rh negative (Rh -) has no protein in bloodblood

Rh+ is dominantRh+ is dominant

Blood TypingBlood Typing

Blood TypeBlood Type Anti-a SeraAnti-a Sera Anti-b SeraAnti-b Sera

AA ClumpingClumping No clumpingNo clumping

BB No clumpingNo clumping ClumpingClumping

ABAB ClumpingClumping ClumpingClumping

OO No clumpingNo clumping No clumpingNo clumping

Sex-linked genesSex-linked genes

The eggs contain a single X chromosome The eggs contain a single X chromosome and sperm contain either an X or a Yand sperm contain either an X or a Y Sex of the offspring depends on whether the Sex of the offspring depends on whether the

sperm that fertilizes the egg has an X or a Ysperm that fertilizes the egg has an X or a Y Any gene located on a sex chromosome Any gene located on a sex chromosome

(X) is called a (X) is called a sex-linked genesex-linked gene Most are found on the X (2,000) and few on Most are found on the X (2,000) and few on

the Y (24)the Y (24)

Sex-linked traitsSex-linked traits

Written as a XWritten as a XRRXXr r for heterozygous.for heterozygous. Y chromosome carries no allele and Y chromosome carries no allele and

the phenotype is dependant upon the phenotype is dependant upon the woman’s allelethe woman’s allele

Therefore, males carry one allele for Therefore, males carry one allele for a sex-linked trait.a sex-linked trait.

Sex-linked disordersSex-linked disorders

Red-green blindnessRed-green blindness Hemophilia (inability of blood to clot)Hemophilia (inability of blood to clot)