Presentation on theme: "Non-Mendelian Genetics. Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics. Traits can be controlled."— Presentation transcript:
Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics. Traits can be controlled by more than one gene. Some alleles are neither dominant nor recessive.
Incomplete Dominance One allele is not completely dominant over another. 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)
Codominance Two alleles are both expressed as a dominant phenotype Coat color in cows RR: Red WW: White RW: Roan, white with red spots (NOT pink!)
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 genes.
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.
Hemophilia Recessive trait Disorder where individuals are missing the normal blood clotting protein. Uncontrolled bleeds from minor cuts or bruises. Female hemophiliac: X h X h Female carrier: X h X Normal: XX Male hemophiliac: X h Y Normal: XY
Colorblindness Recessive Inability to see certain colors
Duchenne Muscular Dystrophy Recessive Progressive weakening and loss of skeletal muscle. Defective version of gene that codes for muscle protein
EXAMPLES!! 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 homozygous for normal blood clotting marries a man who has hemophilia. What are the chances of them having a son or daughter with hemophilia?
-A pedigree is a chart for tracing genes in a family. - When more than one individual in a family is afflicted with a disease, it suggests that the disease might be inherited. Pedigrees
Introduction to Pedigree Symbols -Males are represented by squares. -Females are represented by circles. -Filled symbols show individuals who exhibit the trait in question. -A horizontal line between two symbols represents a mating. -A vertical line descends from parents to a horizontal line shared by all their offspring. -A diagonal line through a symbol indicates that person is deceased. -Roman numerals (I, II, III,…) represent generations. -Arabic numerals (1, 2, 3,…) represent the birth order of siblings. -Specific combinations of numerals (like II-3) uniquely identify each individual in the pedigree.
Phenotypes are used to infer genotypes on a pedigree. Autosomal genes show different patterns on a pedigree than sex-linked genes.
If the phenotype is more common in males, the gene is likely sex-linked.
THE STEPS WHEN INTERPRETING A PEDIGREE CHART -Determine if the pedigree chart shows an autosomal or X- linked disease. -If most of the males in the pedigree are affected, then the disorder is X-linked -If it is a 50/50 ratio between men and women the disorder is autosomal.
-Determine whether the disorder is dominant or recessive. -If the disorder is dominant, one of the parents must have the disorder. -If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.