Presentation on theme: "ABO blood groups. Table 14.2 Multiple alleles ABO blood group s There are 3 different alleles, I A, I B, and i Allele I A makes a cell surface antigen,"— Presentation transcript:
Table 14.2 Multiple alleles ABO blood group s There are 3 different alleles, I A, I B, and i Allele I A makes a cell surface antigen, symbolized with a triangle I B makes a different antigen, symbolized as a circle i makes no antigen
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: I A = N-acetyl-galactosamine I B = 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 Multiple alleles ABO blood group s
The Human ABO Blood Group System Multiple alleles ABO blood group s
The Human ABO Blood Group System multiple alleles codominance Multiple alleles ABO blood group s
Codominance in the Human ABO Blood Group System Dominance Codominance Multiple alleles ABO blood group s
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 - X A Y Female - X A X A or X A X a No Expression: Male - X a Y Female - X a X a 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 - X a Y Female - X a X a No Expression: Male - X A Y Female - X A X A or X A X a (Carrier) Most Sex-linked traits are Recessive! Sex linked inheritance
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 AAaa
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 = X R Y Female = X R X r XRYXRYXRXrXRXr XRYXRY XrYXrY XRXRXRXR XRXrXRXr
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. (X A Y x X A X a ) For a daughter to have the trait, her father must also have it. Her mother must have it or be a carrier. (X a Y, X a X a, X A X a ) The trait often skips a generation from the grandfather to the grandson. If a woman has the trait (X a X a ), all of her sons will be affected. Pedigrees show only female carriers but no male carriers.
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. Polygeny
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
Environmental effects: effect of temperature on pigment expression in Siamese cats Environmental effects