COMPLEX PATTERNS OF INHERITANCE Exceptions to Mendels Laws

COMPLEX PATTERNS OF INHERITANCE Exceptions to Mendel’s Laws

Beyond Mendelian Inheritance • Incomplete Dominance • Dominant allele does not overpower the recessive allele. • Heterozygous genotype has a “blended” phenotype • In snapdragons: RR x ww Rw (pink)

Incomplete Dominance Examples:

Beyond Mendelian Inheritance Polygenic Inheritance: • Occurs when a trait is governed by two or more sets of alleles. • Each dominant allele adds to the affect on the phenotype. • It results in continuous variation of phenotypes within a population. • The traits may also be affected by the environment. • Examples: • Human skin color • Height • Eye color

Polygenic Inheritance Jump to long image description

Co-Dominance: • Two alleles are dominant for the same trait. • When both dominant alleles are present in the genotype, both phenotypes physically show up together in equal proportions. • In chickens, • B=black • W=white • BW=speckled (black and white)

Codominance Examples:

ROAN COW - What happens when you cross a white and a red cow? Roan is codominant - both alleles R and W are expressed

What happens when two Roan Cows are Crossed?

BLOOD TYPES Genes controlling blood types were 1 st genes to be identified ABO & Rh blood groups ( + and - )

Multiple Allele Trait- ABO Blood Group- • Controlled by 3 alleles: A, B, O • A & B alleles are codominant- both are expressed in the presence of each other • O is recessive to both A & B • The blood type is the phenotype

Genotype Blood Type AA, AO Type A BB, BO Type B AB codominant Type AB (universal recipient) OO recessive Type O (universal donor)

Blood Types Practice Mom has type A blood (genotype AO), dad has type AB blood. What blood types are possible among their children? Mom has heterozygous type B blood , dad has type O blood. What blood types are possible among their children?

Blood Types Examples: (Multiple Alleles & Codominance) 14

Beyond Mendelian Inheritance • X-Linked Inheritance * Females- XX * Males- XY. • The term X-linked is used for genes that have nothing to do with gender. • X-linked genes are carried on the X chromosome. • The Y chromosome does not carry these genes.

X-Linked Inheritance-1

Beyond Mendelian Inheritance • Several X-linked recessive disorders occur in humans: • Color blindness • The allele for the blue-sensitive protein is autosomal. • The alleles for the red- and green-sensitive pigments are on the X chromosome. • Muscular dystrophy • Causes wasting away of the muscle • It is caused by the absence of the muscle protein dystrophin. • Hemophilia • It is an absence or minimal presence of clotting factor VIII or clotting factor IX. • An affected person’s blood either does not clot or clots very slowly.

COLORBLIND TEST

Young children are given pictures instead of numbers

COLORBLINDNESS IS ALSO SEX LINKED What happens when a woman who is a CARRIER (b) marries a normal man (B)? What happens when a colorblind man marries a normal woman?

Sex-Linked Examples: