To Mendel and BEYOND!! Mendel was fortunate to use pea plants because each trait that he observed was not only controlled by one set of genes, but there were also two alleles – dominant vs. recessive. Many traits are not that simple!! Other patterns of inheritance include: –Incomplete dominance –Codominance –Multiple Alleles –Polygenic traits

Incomplete Dominance Pattern of inheritance where the dominant trait does not completely “mask” the recessive trait resulting in a blending of the two traits Example: Snapdragons and Four O’Clock flowers –Red x White  Pink

Snapdragons & Four O’Clocks

Incomplete Dominance in Snapdragons Alleles: - Red = R - White = W Genotypes: - RR - WW Phenotypes: - Red - White Genotypes: - RW Phenotypes: - Pink RRWW RW RRRW WW

RR X WW 100% RW Therefore, 100% PINK! RW RR W W Why did the F1 generation only have pink flowers? What happened to the red flowers and the white flowers?

RW RR Heterozygous Crosses What would be the results if the crosses made were between two heterozygous plants? RW x RW The results are as follows: –Genotype: 1 RR: 2 RW: 1 WW –Phenotype: 1 red: 2 pink: 1 white WW R W R W

Codominance Pattern of inheritance where both alleles are dominant and both are expressed independently. Example: Cows –NOT PINK CATTLE... Both red and white fur are present... known as roan. –White cow x red bull  roan

Working with Codominance Red Allele: F R White Allele: F W Red Bull’s Genotype: F R F R White Cow’s Genotype: F W F W The Cross: F R F R x F W F W Roan Genotype: F R F W FRFR FRFR FRFR FRFR FRFR FRFR FWFW FWFW FWFW FWFW FWFW FWFW

Working with Codominance If the cross were between two roan cows: F R F W x F R F W Show a Punnett Square: FRFR FRFR FRFR FRFR FWFW FWFW FWFW FWFW FWFW FWFW FRFR FRFR Genotypic ratio: 1 F R F R :2F R F W :1F W F W Phenotypic ratio: 1 red:2roan:1white

X

Multiple Alleles Mendel worked with traits that had only two alleles: –Pea Flower Color: Purple (P) vs. white (p) –Pea Plant Height: Tall (T) vs. short (t) –Pea Color: Yellow (Y) vs. green (y) Many traits are controlled by more than just two alleles; therefore they are called multiple alleles.

Examples of Multiple Alleles Rabbit fur: In rabbits, coat color is controlled by multiple alleles. Full color (C), white (c), light-gray or chinchilla (c ch ) and white with black points or a Himalayan (c h ). Full color is dominant to all the other alleles. Chinchilla is dominant to Himalayan and white.

ABO Blood Typing ABO blood grouping in people is classic example of multiple alleles in a SINGLE gene Four Blood Types: –A–A –B–B –AB –O–O

Why is it Multiple Alleles? IF it was just simple, there would be only be three genotypes: II ( homozygous dominant ), Ii ( heterozygous ), or ii ( homozygous recessive ). Blood typing is an example of multiple alleles because it has more than two alleles There’s more than just dominant ( I ) and recessive (i) However, there are three different alleles: –I A (dominant) –I B (dominant) –i (recessive) Two forms of the dominant allele!

Genotypes of Blood Types Type A –I A I A or I A i Type B –I B I B or I B i Type O –ii Type AB –IAIB–IAIB

Each allele codes for a specific ANTIGEN that’s found on the surface of the red blood cells: I A = antigen A (protein A) I B = antigen B (protein B) i = no antigen The antibodies in the blood “attack” the antigens making mixed red blood cells to clump.

Summary of Blood Types

Blood Type Patterns Type A can receive A or O Type B can receive B or O Type O can only receive type O Type AB can receive from any blood type (universal recipient) Type O can give blood to any blood type (universal donor) Type AB can only give to other AB

Polygenic Traits Traits that are controlled by two or more genes Not to be confused with genes with multiple alleles!! (One set vs. many sets) In humans: skin color, eye color, height Ex: gene A; gene B; gene D; gene E Each gene would have two alleles: dominant and recessive ( A & a; B & b... Etc )

Interpreting Polygenic Genotypes Skin Color: Dominant allele = pigment Recessive allele = no pigment A, B, D, E = pigment a, b, d, e = no pigment AABBDDEE = 8 dominant: 0 recessive aabbddee = 0 dominant: 8 recessive Which is darkest? Which is lightest?

Interpreting Polygenic Genotypes How many variations are there for AABBDDEE or aabbddee? Only one way to get 8 dominant or 8 recessive alleles Consider genotype: AaBbDdEe How many dominant alleles? How many recessive? What can you infer about the skin color?

Interpreting Polygenic Genotypes Is there another way to get 4 dominant alleles and 4 recessive alleles within the genotype? Examples: AAbbDdEe and aaBBDdEe Each example above have 4 dominant alleles and 4 recessive; therefore, their phenotypes are the same as AaBbDdEe!

Interpreting Polygenic Genotypes The intermediate combination occurs most frequently; therefore, most in a population show that particular phenotype and the two extremes show up the least This pattern is also seen in height!

Polygenic Traits – Skin Color

Polygenic Traits in Humans

Heterochromia

Famous People with Heterochromia Kate Bosworth Mila Kunis Max Scherzer

Heterochromia in Pets

Albinism

Albino Animals

X-linked Disorders (also known as sex-linked)

X-linked Genes located on the X-chromosome Women = two X chromosomes Men = only one X chromosome Disorder occurs more often in males than females Examples: Color blindness, hemophilia, muscular dystrophy

Test for Color Blindness Ishihara Test

Hemophilia

Color Blindness