BEYOND MENDELS OBSERVATIONS OF INHERITANCE

BEYOND MENDELS OBSERVATIONS OF INHERITANCEBEYOND MENDELS OBSERVATIONS OF INHERITANCEHow can we explain inheritance patterns that do not follow simple Mendelian genetics?

Incomplete Dominance Co-dominanceMultiple AllelesINCOMPLETE DOMINANCEA cross between organisms with two different phenotypes produces offspring with a THIRD phenotype that is a BLENDING of the parental traits- The alleles for the same gene cannot completely conceal the presence of the otherINCOMPLETE DOMINANCE

INCOMPLETE DOMINANCEExample:

P: Red Flower x White Flower

F1: Pink FlowerINCOMPLETE DOMINANCEWe can still use the punnett square to solve problems of incomplete dominance

We represent the different phenotypes using all CAPITAL lettersINCOMPLETE DOMINANCECR = Red flowersCW = White flowersCRCW = Pink flowers

Example:

P: Red Flower x White Flower CRCR x CWCW

F1: Pink Flower CRCW

INCOMPLETE DOMINANCECRCRCWCRCW

CRCW

CWCRCW

CRCW

INCOMPLETE DOMINANCEExample: In northeast Kansas there is a creature known as a wildcat. It comes in three colours: blue, red and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BBBB) individual is blue, a homozygous (BRBR) individual is red, and a heterozygous (BBBR) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?INCOMPLETE DOMINANCEBBBBBRBBBR

BBBR

BRBBBR

BBBR

GENTYPIC RATIO:100 % BBBB

PHENOTYPIC RATIO:100% PurpleINCOMPLETE DOMINANCEBBBBBRBBBR

BBBR

BRBBBR

BBBR

GENTYPIC RATIO:100 % BBBB

PHENOTYPIC RATIO:100% Purple

What are the ratios for the F2 generation?INCOMPLETE DOMINANCEHUMAN DISEASE

FAMILIAL HYPERCHOLESTEROLEMIAPrevents tissues from removing low-density lipoproteins (LDLs) from the blood causing high levels of cholesterol in the bloodstreamMutation in the LDLR geneAutosomal dominantHomozygous dominant: 6x amount LDL in bloodHeterozygous: 2x amount LDL in bloodHomozygous recessive: unaffectedINCOMPLETE DOMINANCEHUMAN DISEASE

FAMILIAL HYPERCHOLESTEROLEMIA

CO-DOMINANCEA cross between organisms with two different phenotypes produces offspring with a THIRD phenotype in which BOTH TRAITS appear together- Both alleles are fully expressedCO-DOMINANCE

CO-DOMINANCEExample:

P:Red hair cow x White hair cow

F1: Roan cowCO-DOMINANCEWe can still use the punnett square to solve problems of incomplete dominance

We represent the different phenotypes using all CAPITAL lettersCO-DOMINANCECR = Red hair cowCW = White hair cowCRCW = Roan hair cow

Example:

P:Red hair cow x White hair cow CRCR x CWCW

F1: Roan hair cow CRCW

CO-DOMINANCECRCRCWCRCW

CRCW

CWCRCW

CRCW

CO-DOMINANCEExample:

Predict the phenotypic ratio of offspring when a white hair cow is crossed with a roan bull.

CO-DOMINANCECWCWCRCRCW

CRCW

CWCWCW

CWCW

GENTYPIC RATIO:1 CRCW : 1CWCW

PHENOTYPIC RATIO:1 White hair cow : 1 Roan hair bull

CO-DOMINANCEHUMAN DISEASE

SICKLE CELL ANEMIAResults in mishaped red blood cells that do not transport oxygen efficiently because they cannot pass through small blood vesselsGenotypes:- HbAHbA = Normal- HbSHbS = Sickle Cell- HbAHbS = Some normal and some sickle cells (also resistant to malaria)CO-DOMINANCEHUMAN DISEASE

SICKLE CELL ANEMIA

MULTIPLE ALLELESMore than two alleles code for a specific traitAny individual only has two alleles for each gene (one on each homologous chromosome)Many DIFFERENT ALLELES for a gene can existMULTIPLE ALLELESHUMAN BLOOD GROUPSA single gene determines a persons ABO blood typeThis gene determines what type of antigen protein (if any) is attached to the cell membrane of red blood cellsAntigen: molecule that stimulates the bodys immune systemMULTIPLE ALLELESHUMAN BLOOD GROUPS

MULTIPLE ALLELESHUMAN BLOOD GROUPS

BLOOD TYPEGENOTYPEANTIGEN PRESENTANTIBODY PRESENTAIAIA or IAiABBIBIB or IBiBAABIAIBA and BNoneOiiNoneA and BENVIRONMENTAL EFFECTS ON COMPLEX PATTERNS OF INHERITANCEEnvironmental conditions affect the expression of traits- Example: temperature affects the colouring on Himalayan rabbitsPOLYGENIC INHERITANCECONTINUOUS VARIATION: a range of variation in one trait resulting from the activity of many genesEx: height, skin colour,

POLYGENIC TRAITS: trait controlled by more than one gene (polygenes)Ex: skin colour