There are 3 different alleles, IA, IB, and i Multiple alleles ABO blood group s Table 14.2 There are 3 different alleles, IA, IB, and i Allele IA makes a cell surface antigen, symbolized with a triangle IB makes a different antigen, symbolized as a circle i makes no antigen

3 alleles are present in the human population: Multiple alleles ABO blood group s Human ABO Blood Groups Gene “I” specifies which sugar is found on the outside of red blood cells 3 alleles are present in the human population: IA = N-acetyl-galactosamine IB = galactose i (also referred to as o) = no sugar present 6 possible genotypes

Multiple alleles ABO blood group s Immunology 101 Sugar on the blood cell is an antigen* (A, B, A and B, or none) Your immune system thinks your own antigens are fine Your immune system makes antibodies against non-self antigens Antibodies recognize and target cells with antigens for destruction *something that elicits an immune response

The Human ABO Blood Group System Multiple alleles ABO blood group s The Human ABO Blood Group System With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.  A very very very very very common phenotype used in questions about codominance is roan fur in cattle. Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  A good example of codominance. Another example of codominance is human blood type AB, in which two types of protein ("A" & "B") appear together on the surface of blood cells.

The Human ABO Blood Group System Multiple alleles ABO blood group s The Human ABO Blood Group System multiple alleles With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.  A very very very very very common phenotype used in questions about codominance is roan fur in cattle. Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  A good example of codominance. Another example of codominance is human blood type AB, in which two types of protein ("A" & "B") appear together on the surface of blood cells. codominance

Codominance in the Human ABO Blood Group System Multiple alleles ABO blood group s Codominance in the Human ABO Blood Group System Dominance Dominance Codominance

Sex linked inheritance Sex-linked traits are produced by genes only on the X chromosome. They can be Dominant or Recessive. A = dominant a = recessive What would be the genotypes of a male and female that have a Sex-linked Dominant trait and do not express the trait? Expresses Trait: Male - XA Y Female - XA XA or XA Xa No Expression: Male - Xa Y Female - Xa Xa What would be the genotypes of a male and female that have a Sex-linked Recessive trait and do not express the trait? Expresses Trait: Male - Xa Y Female - Xa Xa No Expression: Male - XA Y Female - XA XA or XA Xa (Carrier) Most Sex-linked traits are Recessive!

Gene located on the X chromosome More males than females affected (males inherit X from mother) Females can only inherit if the father is affected and mother is a carrier (hetero) or affected (homo) An affected female will pass the trait to all her sons Daughters will be carriers if father is not affected Males cannot be carriers (only have 1 X so either affected or not) Can skip generations (hide) E.g. color blindness, hemophilia, Duchene muscular dystrophy

Sex Linked Problems: Red-green color blindness in men is caused by the presence of a sex-linked recessive gene c, whose normal allele is C. a) Can two color blind parents produce a normal son? b) Can they produce a normal daughter? c) Can two normal parents produce a colorblind son or daughter? d) Can a normal daughter have a colorblind father or mother? e) Can a colorblind daughter have a normal father or mother?

Sex influenced traits A phenotypic characteristic or trait that is expressed differently in males and females male pattern baldness

How to Construct a Pedigree A Pedigree is a visual showing the pattern of inheritance for a trait. (Family tree) Symbols and Rules: Male = Female = Affected = Unaffected = Carrier = Link parents together with a line and then make a vertical line to connect to offspring.

Autosomal Dominant Pedigree Draw a Pedigree showing a cross between Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities) Genotypes of Affected and Unaffected: AA and Aa = Affected aa = Unaffected Aa AA aa

Autosomal Recessive Pedigree Draw a Pedigree showing a cross between Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities) Genotypes of Affected and Unaffected: AA=Unaffected Aa=Carrier, Unaffected aa=Affected Aa AA aa

Sex-Linked Recessive Pedigree Draw a Pedigree showing a cross between a Red eyed Male fruit fly and a Carrier Female fruit fly which have 2 males and 2 females. (Show all possibilities) Red is dominant to white. Genotypes of Parents: Male = XR Y Female = XR Xr XRY XRXr XrY XRXR

Characteristics of Autosomal Dominant, Autosomal Recessive, and Sex-linked Recessive Traits In groups, analyze your notes on each type of disorder and examine the pedigrees. Come up with rules/characteristics for each type of Trait.

Autosomal Dominant Traits Heterozygotes are affected Affected children usually have affected parents. Two affected parents can produce an unaffected child. (Aa x Aa) Two unaffected parents will not produce affected children. (aa x aa) Both males and females are affected with equal frequency. Pedigrees show no Carriers.

Autosomal Recessive Traits Heterozygotes are carriers with a normal phenotype. Most affected children have normal parents. (Aa x Aa) Two affected parents will always produce an affected child. (aa x aa) Two unaffected parents will NOT produce affected children unless both are carriers. (AA x AA, AA x Aa) Affected individuals with homozygous unaffected mates will have unaffected children. (aa x AA) Close relatives who reproduce are more likely to have affected children. Both males and females are affected with equal frequency. Pedigrees show both male and female carriers.

Sex-Linked Recessive Traits More males than females are affected. An affected son can have parents who have the normal phenotype. (XAY x XAXa) For a daughter to have the trait, her father must also have it. Her mother must have it or be a carrier. (XaY, XaXa, XAXa) The trait often skips a generation from the grandfather to the grandson. If a woman has the trait (XaXa), all of her sons will be affected. Pedigrees show only female carriers but no male carriers.

AA = dark Aa = less dark aa - light Polygeny Polygenic inheritance: additive effects (essentially, incomplete dominance) of multiple genes on a single trait AA = dark Aa = less dark aa - light And similarly for the other two genes - in all cases dominance is incomplete for each gene. Think of each “capital” allele (A, B, C) as adding a dose of brown paint to white paint.

environment often influences phenotype Environmental effects environment often influences phenotype the norm of reaction = phenotypic range due to environmental effects norms of reactions are often broadest for polygenic characters. Blue require low pH

Environmental effects: effect of temperature on pigment expression in Siamese cats