Patterns of Patterns of InheritanceInheritance

Complete DominanceComplete Dominance

Incomplete DominanceIncomplete Dominance

Co-dominanceCo-dominance

Co-dominance with Multiple Co-dominance with Multiple AllelesAlleles

Sex LinkedSex Linked

Impact of Impact of Mendel’sMendel’s Work Work

Mendel published his results in 1866Mendel published his results in 1866 Paper received little noticePaper received little notice Mendel discontinued his experiments Mendel discontinued his experiments

in 1871in 1871 Paper rediscovered in 1900 Paper rediscovered in 1900

Mendel’s Law of Mendel’s Law of SegregationSegregation

An individual inherits ONE “unit” of An individual inherits ONE “unit” of information (allele) about a trait from information (allele) about a trait from each parenteach parent

During gamete formation, the alleles During gamete formation, the alleles separate from each other (Tt T or t )separate from each other (Tt T or t )

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Mendel’s Law of Mendel’s Law of Independent AssortmentIndependent Assortment

Mendel concluded that one gene did not Mendel concluded that one gene did not affect another geneaffect another gene

Alleles for these genes separated Alleles for these genes separated random from each otherrandom from each other

TtRr TtRr T or t R or r T or t R or r so TR Tr tR trso TR Tr tR tr

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Complete Complete DominancDominanc

e e InheritancInheritanc

ee

True-breedinghomozygous recessiveparent plant

True-breedinghomozygous dominantparent plant

An F1 plantself-fertilizesand producesgametes:

F1 PHENOTYPE

S

F2 PHENOTYPE

S

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 2 alleles; one 2 alleles; one

dominant or the otherdominant or the other

if dominant allele if dominant allele present, it will be present, it will be expressed expressed

2 distinct 2 distinct phenotypes; 3:1 ratiophenotypes; 3:1 ratio

Genetics After Genetics After MendelMendel

1. Incomplete Dominance1. Incomplete Dominance

2. Co-dominance2. Co-dominance

3. Co-dominance with Multiple 3. Co-dominance with Multiple AllelesAlleles

4. Sex Linked4. Sex Linked

Incomplete Incomplete DominanceDominance

XHomozygous parent

Homozygous parent

All F1 are heterozygous

X

F2 shows three phenotypes in 1 : 2 : 1 ratio

1. Incomplete Dominance neither allele is neither allele is

completely completely dominant over dominant over the otherthe other

3 phenotypes3 phenotypes

heterozygous heterozygous is a is a “intermediate “intermediate or “blend”or “blend”

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R R r r

R r

R r

R r

R RR rr r R r

both alleles are both alleles are expressed at the expressed at the same time in the same time in the heterozygous (roan)heterozygous (roan)

3 phenotypes;3 phenotypes;

1 : 2 : 1 ratio1 : 2 : 1 ratio

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2.Co-dominance

3. Co-3. Co-dominance dominance with Multiple with Multiple

Alleles:Alleles:ABO Blood ABO Blood

typestypes

3 alleles; two that are co-dominant 3 alleles; two that are co-dominant and one recessiveand one recessive

IIAA , I , IBB , i , i page page

Genotype Phenotype

IAIA or IAi Type A

IBIB or IBi Type B

IAIB Type AB

ii Type O

ABO Blood TypesABO Blood Types type of blood determined by type of blood determined by antigenantigen on surface (flag) on surface (flag)

type of blood make type of blood make antibodiesantibodies against other antigens against other antigens

Blood TransfusionsBlood Transfusions During transfusions recipient’s antibodies in plasma During transfusions recipient’s antibodies in plasma

will attack blood cells that have an unfamiliar surface will attack blood cells that have an unfamiliar surface

antigen (antigen (agglutinationagglutination – clumping of blood) – clumping of blood)

Type AB is Type AB is universal recipientuniversal recipient since it does not since it does not

have any antibodies because it has both antigens – have any antibodies because it has both antigens –

any blood can be donated to them!any blood can be donated to them!

Type O is Type O is universal donoruniversal donor since it has neither type A since it has neither type A

nor type B antigen for antibodies to attack – give to nor type B antigen for antibodies to attack – give to

anyoneanyone

TransfusionsTransfusions

AntibodieAntibodiess

Can Can Receive Receive

Blood Blood FromFrom

Type AType A BB A or OA or O

Type BType B AA B or OB or O

Type ABType AB nonenone A, B, AB, OA, B, AB, O

Type OType O A and BA and B only Oonly O

Rh FactorRh Factor another protein marker on red blood another protein marker on red blood

cellscells independent of type of bloodindependent of type of blood inheritance works according to complete inheritance works according to complete

dominancedominance either Rh+ or Rh- ; Rh+ is dominant either Rh+ or Rh- ; Rh+ is dominant special problem during pregnancy of special problem during pregnancy of

second child if mom is Rh- and first was second child if mom is Rh- and first was baby Rh+baby Rh+

4. Sex Linked4. Sex Linked genes on the sex genes on the sex

chromosomeschromosomes

have different have different probabilities in probabilities in females and females and malesmales

examples of examples of recessive X recessive X linked traits linked traits – – hemophiliahemophilia

– – red/green red/green colour blindness colour blindness

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Other types of InheritanceOther types of Inheritance5. Multifactorial/Multiple 5. Multifactorial/Multiple

Genes/PolygenicGenes/Polygenic

6. Sex Limited6. Sex Limited

7. Sex Influenced7. Sex Influenced

8. Gene Linkage8. Gene Linkage

5. Multifactorial/Multiple 5. Multifactorial/Multiple Genes/PolygenicGenes/Polygenic

Traits show wide range of phenotypic Traits show wide range of phenotypic expression; continuous distributionexpression; continuous distribution

Controlled by more than one geneControlled by more than one gene

Traits maybe influenced by other Traits maybe influenced by other factorsfactors

Examples human hair colour, height, Examples human hair colour, height, eye colour, skin coloureye colour, skin colour

Describing Continuous Describing Continuous Distribution Distribution

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)

6. Sex Limited Traits6. Sex Limited Traits

Expression of the trait is limited by sex Expression of the trait is limited by sex of the individualof the individual

Traits NOT on sex chromosomeTraits NOT on sex chromosome Thought to be influenced by hormonesThought to be influenced by hormones Example: heavy beards – phenotype in Example: heavy beards – phenotype in

males only but females inherit but don’t males only but females inherit but don’t express it but can pass trait to sonsexpress it but can pass trait to sons

7. Sex Influenced Traits7. Sex Influenced Traits Idea of how genes are influenced by Idea of how genes are influenced by

internal environmentsinternal environments

Genes may be dominant in one sex Genes may be dominant in one sex but recessive in other; genotype but recessive in other; genotype interpreted differentlyinterpreted differently

Baldness – dominant trait in males; in Baldness – dominant trait in males; in females recessive trait and don’t see females recessive trait and don’t see “bald” but rather thin“bald” but rather thin

Nature verse NurtureNature verse Nurture Expression of traits are not fully under control Expression of traits are not fully under control

of just what your genotype is (NATURE)of just what your genotype is (NATURE)

An organism’s internal environment and An organism’s internal environment and external environmental factors influence how external environmental factors influence how genes may be expressed (NURTURE)genes may be expressed (NURTURE)

Example – height – may have genetics to be Example – height – may have genetics to be tall but if there is hormonal imbalance or tall but if there is hormonal imbalance or nutritional deficiency than won’t reach nutritional deficiency than won’t reach genetic potentialgenetic potential

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 heat-sensitive version of an enzyme in melanin-an enzyme in melanin-producing pathwayproducing pathway

Melanin is produced in Melanin is produced in cooler areas of bodycooler areas of body

Environmental Effects on Environmental Effects on Plant PhenotypePlant Phenotype

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 Flower color ranges from pink to blueblue