Non-Mendelian Genetics

Mendelian Genetics: Dominant & Recessive Review One allele is DOMINANT over the other (because the dominant allele can “mask” the recessive allele) genotype: PP genotype: pp genotype: Pp phenotype: purple phenotype: white phenotype: purple

Review Problem: Dominant & Recessive In pea plants, purple flowers (P) are dominant over white flowers (p). Show the cross between two heterozygous plants. P p GENOTYPES: - PP (25%) Pp (50%) pp (25%) - ratio 1:2:1 P p PP Pp Pp pp PHENOTYPES: - purple (75%) white (25%) - ratio 3:1

Non-Mendelian Genetics Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex-Linked Traits

Incomplete Dominance a third (new) phenotype appears in the heterozygous condition as a BLEND of the dominant and recessive phenotypes. Ex - Dominant Red (R) + Recessive White (r) = Hybrid Pink (Rr) RR = red rr = white Rr = pink

Problem: Incomplete Dominance Show the cross between a pink and a white flower. GENOTYPES: R r - RR (0%) Rr (50%) rr (50%) - ratio 1:1 r Rr rr Rr rr PHENOTYPES: - pink (50%); white (50%) - ratio 1:1

Codominance NS = some of each NN = normal cells SS = sickle cells sick in the heterozygous condition, both alleles are expressed equally with NO blending! Represented by using two DIFFERENT capital letters. Example: Dominant Black (B) + Dominant White (W) = Speckled Black and White Phenotype (BW) Sickle Cell Anemia - NS = some of each NN = normal cells SS = sickle cells sick

Codominance Example: Speckled Chickens BB = black feathers WW = white feathers BW = black & white speckled feathers Notice – NO GRAY! NO BLEND! Each feather is either black or white

Codominance Example: Rhodedendron R = allele for red flowers W = allele for white flowers Cross a homozygous red flower with a homozygous white flower.

Codominance Example: Roan cattle cattle can be red (RR – all red hairs) white (WW – all white hairs) roan (RW – red and white hairs together)

Codominance Example: Appaloosa horses Gray horses (GG) are codominant to white horses (WW). The heterozygous horse (GW) is an Appaloosa (a white horse with gray spots). Cross a white horse with an appaloosa horse. W W G W GW GW WW WW

Problem: Codominance Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. N S GENOTYPES: - NS (50%) SS (50%) - ratio 1:1 S NS SS PHENOTYPES: - carrier (50%) sick (50%) - ratio 1:1

Multiple Alleles there are more than two alleles for a gene. Ex – blood type consists of two dominant and one recessive allele options. Allele A and B are dominant over Allele O (i)

Multiple Alleles: Lab Mouse Fur Colors Fur colors (determined by 4 alleles): black agouti yellow

Multiple Alleles: Rabbit Fur Colors Fur colors (determined by 4 alleles): full, chinchilla, himalayan, albino

Multiple Alleles: Blood Types (A, B, AB, O) Rules for Blood Types: A and B are co-dominant (Both show) AA or IAIA = type A BB or IBIB = type B AB or IAIB = type AB A and B are dominant over O (Regular dom/rec) AO or IAi = type A BO or IBi = type B OO or ii = type O

Multiple Alleles: Blood Types (A, B, AB, O)

Allele (antigen) on RBC surface Phenotype Possible Genotype(s) Allele (antigen) on RBC surface Can Donate Blood To Can Receive Blood From A IAi IAIA A, AB A, O B IBi IBIB B, AB B, O AB IAIB A, B, AB, O O ii

Problem: Multiple Alleles Show the cross between a mother who has type O blood and a father who has type AB blood. GENOTYPES: i i - Ai (50%) Bi (50%) - ratio 1:1 A B Ai Bi PHENOTYPES: - type A (50%) type B (50%) - ratio 1:1

Problem: Multiple Alleles Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood. GENOTYPES: A i AB (25%); Bi (25%); Ai (25%); ii (25%) - ratio 1:1:1:1 B i AB ii Bi Ai PHENOTYPES: type AB (25%); type B (25%) type A (25%); type O (25%) - ratio 1:1:1:1

Polygenic Traits traits produced by multiple genes example: skin color

Sex-Linked Traits Gene is attached to the X chromosome only, not found on the Y chromosome at all. (women have XX, men have XY chromosomes). These disorders are more common in boys. examples: red-green colorblindness

Sex-Linked Traits in males, there is no second X chromosome to “mask” a recessive gene. If they get an X with the disorder, they have it. Girls must inherit defective X’s from both parents.

Sex-Linked Traits A: 29, B: 45, C: --, D: 26  Normal vision  Red-green color blind A: 70, B: --, C: 5, D: 6  Red color blind A: 70, B: --, C: 5, D: 2  Green color blind