Incomplete dominance

 Occurs when neither allele ‘dominates’ the other.

Incomplete dominance  Occurs when neither allele ‘dominates’ the other.  When both alleles are present in the heterozygous genotype, they both contribute to produce a phenotype that is a blend of the genetic information.

Incomplete dominance  Occurs when neither allele ‘dominates’ the other.  When both alleles are present in the heterozygous genotype, they both contribute to produce a phenotype that is a blend of the genetic information.  Therefore, three different phenotypes may occur.

Incomplete dominance  Occurs when neither allele ‘dominates’ the other.  When both alleles are present in the heterozygous genotype, they both contribute to produce a phenotype that is a blend of the genetic information.  Therefore, three different phenotypes may occur.  EG – pure-breeding red (RR) x pure-breeding white (rr) produces all pink (Rr) offspring (such as snapdragons).

Incomplete dominance  Occurs when neither allele ‘dominates’ the other.  When both alleles are present in the heterozygous genotype, they both contribute to produce a phenotype that is a blend of the genetic information.  Therefore, three different phenotypes may occur.  EG – pure-breeding red (RR) x pure-breeding white (rr) produces all pink (Rr) offspring (such as snapdragons).  EG – Rr crossed to produce (see board for punnett)

Incomplete dominance  Occurs when neither allele ‘dominates’ the other.  When both alleles are present in the heterozygous genotype, they both contribute to produce a phenotype that is a blend of the genetic information.  Therefore, three different phenotypes may occur.  EG – pure-breeding red (RR) x pure-breeding white (rr) produces all pink (Rr) offspring (such as snapdragons).  EG – Rr crossed to produce (see board for punnett) 1 Red, 2 pink, 1 white

Co-dominance  Occurs when both alleles are equally dominant – when both alleles are present in the heterozygous genotype they are both expressed in the phenotype.

Co-dominance  Occurs when both alleles are equally dominant – when both alleles are present in the heterozygous genotype they are both expressed in the phenotype.  3 phenotypes can occur  EG – Both alleles give capital letters. R for red and W for white for coat colour.

Co-dominance  Occurs when both alleles are equally dominant – when both alleles are present in the heterozygous genotype they are both expressed in the phenotype.  3 phenotypes can occur  EG – Both alleles give capital letters. R for red and W for white for coat colour.  EG – pure-breeding red (RR) x pure-breeding white (WW) produces roan offspring in horses (RW)

Multiple alleles  Occur with genes that have more than two different alleles, though an individual will have only two of the alleles in its genotype.

Multiple alleles  Occur with genes that have more than two different alleles, though an individual will have only two of the alleles in its genotype.  Inheritance of human blood groups shows multiple alleles, complete dominance, and co-dominance.

Multiple alleles  Occur with genes that have more than two different alleles, though an individual will have only two of the alleles in its genotype.  Inheritance of human blood groups shows multiple alleles, complete dominance, and co-dominance.  Three different alleles I A I B I exist for what is the ABO blood grouping. I A and I B are co-dominant; both are completely dominant to i.

Multiple alleles GenotypePhenotype (blood group) IAIAIAIA A IBIBIBIB B IAIBIAIB AB I A iA I B iB iiO I A I B genotype gives AB blood because both the co-dominant alleles are expressed in the phenotype.

Multiple alleles GenotypePhenotype (blood group) IAIAIAIA A IBIBIBIB B IAIBIAIB AB I A iA I B iB iiO I A I B genotype gives AB blood because both the co-dominant alleles are expressed in the phenotype. I A i and I B i give A and B blood because both I A and I B are dominant over i

Multiple alleles examples  Page 89

Lethal Alleles  Occurs when a mutation results in an allele that produces a non-functional version of an essential protein.

Lethal Alleles  Occurs when a mutation results in an allele that produces a non-functional version of an essential protein.  If it is inherited, the individual will die before or shortly after birth.

Lethal Alleles  Occurs when a mutation results in an allele that produces a non-functional version of an essential protein.  If it is inherited, the individual will die before or shortly after birth.  EG – in fruit flies. A mutated allele caused ‘curly’ wings rather than normal wings. The mutated allele is dominant. Flies with homozygous genotype for curly wings do not hatch from their eggs.  Punnett from pg 90