Post on 31-Dec-2015
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