Table 14.2

Table 14.2

Multiple allelesABO blood group s

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

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


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


The Human ABO Blood Group System

multiple alleles

codominance


Codominance in the Human ABO Blood Group System

Dominance

Dominance

Codominance


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!

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 Aa AAaa

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=AffectedAa Aa

Aa 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 = XR Y Female = XR Xr

XRY XRXr

XRY XrY XRXR 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.

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 temperatureon pigment expression in Siamese cats

Environmental effects

Documents

Table 14.2