Complex Patterns of Inheritance Exceptions to Mendel’s rules: not simple dominant/recessive inheritance

The phenotype of the heterozygote is INTERMEDIATE. Incomplete Dominance The phenotype of the heterozygote is INTERMEDIATE. Red + White = Pink

Red parent plant R R RR’ R’ White parent plant R’ All pink offspring!

Both alleles are expressed! Codominance Both alleles are expressed! Cross a Brown and White Cow! B=Brown W=White BW=Brown and White

Multiple Alleles When a gene has more than 2 forms of an allele (conflicts with Mendel’s 2nd conclusion); There are more than just one dominant and one recessive allele Blood Types: A, B, AB, O A and B are codominant O is recessive to both

Type A: IAIA or IAi Type B: IBIB or IBi Type AB: IAIB Type O: ii

http://learn.genetics.utah.edu/content/begin/traits/blood/

Pretend that Brad Pitt is heterozygous for the type B allele and Angelina Jolie is Type O. If they have a child, what are all the possible blood types of their baby? What if he is homozygous for type B?

Polygenic Traits Trait controlled by two or more GENES (not alleles) OR interaction with the environment AaBbCc x AaBbCc Skin Pigmentation Gene to make melanin Gene to bring nutrients to melanin-producing cells (melanocytes) Gene to turn on/off melanin when in continued presence of UV light Traits vary along a bell curve http://waynesword.palomar.edu/lmexer5.htm

Sex-Linked Traits Traits that affect genes on the X chromosome Females: XX Males: XY There are X-linked dominant and X-linked recessive traits Males only have to inherit one version for it to show Females can have a copy of the affected allele on 1 X chromosome and NOT have the disorder Examples of X-linked Dominant Disorders: Vitamin D Rickets Examples of X-linked Recessive Disorders: Male-Pattern Baldness, Color Blindness, Hemophilia Baldness

Vitamin D Rickets Vitamin D allows calcium to be absorbed. No calcium absorption = weak, flimsy bones

Punnett Squares for the sex-linked trait hemophilia Cross a heterozygous (carrier) female for hemophilia with a normal male: XNXn x XNY N = Normal n = hemophilia