Incomplete Dominance, Co-Dominance, and Sex-linked dominance NON-MENDELIAN GENETICS

Incomplete Dominance, Co-Dominance, and Sex-linked dominance NON-MENDELIAN GENETICS

INCOMPLETE DOMINANCE

INCOMPLETE DOMINANCE Two alleles dominant and recessive Genotypes are the same as simple Mendelian genetics: AA, Aa, aa Some phenotypes are different than simple Mendelian genetics When an organism is homozygous dominant, they look dominant When an organism is homozygous recessive, they look recessive When an organism is heterozygous, they are a blend of dominant and recessive

INCOMPLETE DOMINANCE Example flower color Red petals are dominant to white petals A flower with red petals is crossed with a flower that has white petals The offspring will have pink petals

INCOMPLETE DOMINANCE If two heterozygous flowers are crossed, they will give a 1:2:1 genotypic ratio AND a 1:2:1 phenotypic ratio Genotypic Phenotypic

INCOMPLETE DOMINANCE If two heterozygous flowers are crossed, they will give a 1:2:1 genotypic ratio AND a 1:2:1 phenotypic ratio Genotypic 1 RR 2 Rr 1 rr Phenotypic 1 red 2 pink 1 white

CO-DOMINANCE

CO-DOMINANCE The alleles are both dominant; neither is recessive Both alleles are FULLY expressed in the offspring Co-dominant alleles are written as capital letters with superscripts A B

CO-DOMINANCE Example: In chickens, the alleles for feather color are co-dominant (letter for the feather color trait is F). One allele is for white feathers, the other is for black feathers

CO-DOMINANCE Example: In chickens, the alleles for feather color are co-dominant (letter for the feather color trait is F). One allele is for white feathers, the other is for black feathers Black feathers = F B White feathers = F W

CO-DOMINANCE Example: In chickens, the alleles for feather color are co-dominant (letter for the feather color trait is F). One allele is for white feathers, the other is for black feathers Black feathers = F B White feathers = F W Genotype Combinations

CO-DOMINANCE Example: In chickens, the alleles for feather color are co-dominant (letter for the feather color trait is F). One allele is for white feathers, the other is for black feathers Black feathers = F B White feathers = F W Genotype Combinations F B F B F W F W F B F W

CO-DOMINANCE Example: In chickens, the alleles for feather color are co-dominant (letter for the feather color trait is F). One allele is for white feathers, the other is for black feathers Black feathers = F B White feathers = F W Genotype Combinations F B F B = a chicken with only black feathers F W F W = a chicken with only white feathers F B F W = A chicken with BOTH white AND black feathers

CO-DOMINANCE

CO-DOMINANCE BLOOD TYPES Human blood types are an example of codominant traits with multiple alleles (3) Type O is recessive Types A and B are codominant with each other (neither dominates over the other) They are both fully dominant to type O The dominant alleles are written with the letter I and a superscript. The recessive allele is a lowercase i

CO-DOMINANCE BLOOD TYPES Type A Type B Type AB Type O -

CO-DOMINANCE BLOOD TYPES Type A I A I A or I A i Type B I B I B or I B i Type AB I A I B Type O - ii

CO-DOMINANCE BLOOD TYPES

CO-DOMINANCE BLOOD TYPES Example cross One parent is heterozygous for type A blood The second parent is heterozygous for type B blood

CO-DOMINANCE BLOOD TYPES Example cross One parent is heterozygous for type A blood The second parent is heterozygous for type B blood

CO-DOMINANCE BLOOD TYPES What is the genotypic ratio? What is the phenotypic ratio?

CO-DOMINANCE BLOOD TYPES What is the genotypic ratio? 25% I A I B 25% I A i 25% I B i 25% ii What is the phenotypic ratio?

CO-DOMINANCE BLOOD TYPES What is the genotypic ratio? 25% I A I B 25% I A i 25% I B i 25% ii What is the phenotypic ratio? 25% AB 25% A 25% B 25% O

BLOOD TYPE EXAMPLES A child is born to a mother who is homozygous for type B blood and a father who is heterozygous for type A blood. What is the probability the child will have type A blood? Type B blood? A child is born to a mother who has type AB blood and a father who has type O blood. What are the possible blood types for the child?

SEX-LINKED DOMINANCE

SEX-LINKED Traits that are found on the X chromosome are known as sex-linked since they are controlled by one of the sex chromosomes Since females have two X chromosomes, they are more likely to be heterozygous carriers (having one recessive X and one normal X)

SEX-LINKED Since males only have one X chromosome (from their mother), they are more affected than females by recessive sex-linked traits They either have the recessive trait or they don t (they cannot be heterozygous) Examples: color-blindness and hemophilia

COLOR BLINDESS

SEX-LINKED Example: A child is born to a mother who is a carrier for hemophilia, and a father who does not have the disease. Hemophilia is a recessive sex-linked disease. What are the chances that the child will be: A boy with hemophilia? A boy without hemophilia? A girl with hemophilia? A girl without hemophilia?

SEX-LINKED

SEX-LINKED

PEDIGREE

PEDIGREES Used to trace the inheritance of a trait through several generations Uses symbols to illustrate inheritance

PEDIGREE TYPES

PEDIGREES Autosomal Dominant Affected offspring cannot have non-affected parents Examples Huntington s Disease Achondoplasia (dwarfism)

PEDIGREES Autosomal Recessive Non-affected parents can have affected offspring (parents are carriers) If both parents are affected, they MUST have affected offspring Examples Cystic Fibrosis Albinism Tay-Sachs Disease

PEDIGREES X-Linked Dominant Affected fathers must have affected daughters Examples: Fragile X Syndrome (causes autism)

PEDIGREES X-Linked Recessive High incidence of affected males (since they have only one X chromosome) Examples Hemophilia Red/Green Color-blindness

PRACTICE

PRACTICE Identify this pedigree as autosomal recessive, autosomal dominant, X-linked dominant, or X- linked recessive

PRACTICE Identify this pedigree as autosomal recessive, autosomal dominant, X-linked dominant, or X- linked recessive

PRACTICE Identify this pedigree as autosomal recessive, autosomal dominant, X-linked dominant, or X- linked recessive