Non-Mendelian Genetics
Non-Mendelian Genetics Some traits don t follow the simple dominant/recessive rules that Mendel first applied to genetics. Some alleles are neither dominant nor recessive. Sometimes there are more than 2 alleles for each trait Some traits can be controlled by more than one gene. Sometimes traits depend on sex (M or F)
Incomplete Dominance Neither allele is dominant over the other. Both alleles will be capital letters. The heterozygous phenotype is a blending of the two homozygous phenotypes. Example: four o clock flowers RR=red WW=white RW=pink (blending of the two alleles)
Practice Incomplete Dominance: Cross a red and white flower
Practice Incomplete Dominance: Cross two pink flowers
Codominance Both alleles share dominance, so both are expressed (shown) Both alleles are capital letters Coat color in cows RR: Red WW: White RW: Roan, white with red spots (NOT pink!)
Practice Codominance: Cross a red and white cow
Practice Codominance: Now cross two roan cows
Multiple Alleles More than two choices of alleles are present for a trait ABO blood type has three alleles ABO Blood types: A and B are co-dominant (both will be displayed) If both A and B are present, type is AB O is recessive Individuals can be type A, B, AB, or O (recessive)
Multiple Alleles (Blood Type) 6 Genotypes, 4 Phenotypes AA Type A Ao Type A BB Type B Bo Type B AB Type AB oo Type O
Polygenic Traits Some traits are found on more than 1 gene. Each gene has a small effect, and all the genes together have the total effect Examples are often traits with a wide variety (skin color, hair color, eye color)
Eye Color Caused by AT LEAST two genes, with a 3 rd gene suspected but not confirmed Chromosome 15: Brown/blue gene Chromosome 19: Green/blue gene
Eye Color Multiple genes leads to many more variations / possibilities / shades / tones
Skin Color Located on 3 genes (A, B, C) Maximum pigment dominant (A, B, C) Minimum pigment recessive (a, b, c) Darkest color (AABBCC) Lightest color (aabbcc) Results in: 27 genotypes 9 phenotypes
Skin Color Punnett Square
Sex-Linked Inheritance
Review Males have an X and a Y chromosome Females have two X chromosomes These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked traits.
The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome. Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need.
Recessive trait Hemophilia Disorder where individuals are missing the normal blood clotting protein. Uncontrolled bleeds from minor cuts or bruises. Located on X (female) chromosome Much more common in males than females why?
Hemophilia Located on X (female) chromosome Male (XY) needs only one recessive allele Females (XX) need both recessive alleles If H = normal and h = hemophilia, then: Normal Male: X(H) Y Affected Male: X(h) Y Normal Female: X(H) X(H) Carrier Female: X(H) X(h) Affected Femaile: X(h) X(h) very rare
Red/Green Colorblindness Inability to see the colors red and green Located on X chromosome If C = regular and c = colorblind, then: Normal vision male: X(C) Y Colorblind male: X(c) Y Normal/non-carrier female: X(C) X(C) Normal/carrier female: X(C) X(c) Colorblind female: X(c) X(c)
A woman who is heterozygous for normal vision marries a man who is colorblind. What are the chances of them having a son or daughter who is colorblind? **NOTE: You have to use X s and Y s, and read the punnett square separately for boys and girls!**
A woman who is heterozygous for normal vision X(C) X(c) marries a man who is colorblind X(c) Y. What are the chances of them having a son or daughter who is colorblind?
A woman who is homozygous for normal blood clotting X(H) X(H) marries a man who has hemophilia X(h) Y. What are the chances of them having a son or daughter with hemophilia?