Mendel Law Exceptions and Sex Linkage Big Idea 3: Living systems store, retrieve, transmit, and respond to info essential to life processes.

Essential Knowledge 3A4: The inheritance pattern of many traits cannot be explained by simple Mendelian genetics.

Cross white roses (WW) with red roses (RR) Pink roses (RW)! Incomplete Dominance Cross white roses (WW) with red roses (RR) Pink roses (RW)! Heterozygous offspring are in b/t the 2 homozygous phenotypes. BLENDING!

Codominance A condition in which both alleles show up in phenotype. Neither allele is recessive.

Codominance

Codominance: Piebald Black-Pastel Ball Python

Traits that are controlled by 2 or more genes. Polygenic Traits Traits that are controlled by 2 or more genes. Ex: skin/eye color in humans controlled by > 4 genes  Creates wide range of trait

Multiple Alleles Some genes have more than 2 alleles. Ex: Blood type: 4 phenotypes: A, B, AB, O Alleles: i, iA, or iB But, still only get 2 copies of allele, from mom and dad!

(a) The three alleles for the ABO blood groups Fig. 14-11 Allele Carbohydrate IA A IB B i none (a) The three alleles for the ABO blood groups and their associated carbohydrates Red blood cell appearance Phenotype (blood group) Genotype IAIA or IA i A IBIB or IB i B Figure 14.11 Multiple alleles for the ABO blood groups IAIB AB ii O (b) Blood group genotypes and phenotypes

Gene Linkage Genes for traits can be inherited together  linked. Each chromosome is actually a group of linked genes.

Can you tell which traits are linked?

Determination of Sex Girls: XX (homologous sex chroms) X Boys: XY (non-homol. sex chroms) Only ends of Y have regions homologous to X X Y

Found on sex chroms, mainly X (contains more DNA). Sex Linked Genes Found on sex chroms, mainly X (contains more DNA). Easy to spot b/c many males will have trait  XY..if trait is on X, no competition on Y (less DNA)

Fruit Fly Genetics! Good for genetic studies (Drosophila melanogaster:  breed at a high rate  A generation can be bred every 2 weeks  Only have 4 pairs of chromosomes Morgan, an embryologist did many studies with these to locate genes on chromosomes

Wild type = normal phenotype Traits alternative to wild type: mutant phenotypes

Some Traits are Sex Limited and Expression Depends on Sex of Individual

Some Traits Result from Nonnuclear Inheritance Ex: Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells

In Animals… Mitochondrial DNA is passed on by egg, not sperm  inherit mitochondria traits from mom.

Let’s do a Problem!

Sex Linked Fruit Fly Sample Probs and Lab