LESSON TOPIC   COMPLEX PATTERNS OF INHERITANCE

MAIN QUESTION:  How multiple alleles, incomplete dominance, co dominance is affecting the living world?

WHEN HEREDITY FOLLOWS DIFFERENT RULES. 1.INCOMPLETE DOMINANCE – APPEAREANCE OF A THIRD PHENOTYPE. -The phenotype is intermediate between two homozygous parents.   Ex. Capital letters used for both alleles   Snap dragons- red = RR, white= WW, pink = RW

Incomplete dominance

2. Co dominance - expression of both alleles   Occurs when alternative alleles are present in the genotype and fully observed in the phenotype.   See.fig 12.8, pg.323

Codominance in Humans Sickle-cell anemia – sickle red blood cells slow blood flow, produce tissue damage and pain.

3. Multiple phenotypes from multiple alleles - traits controlled by more than two alleles. Ex. Pigeon feathers color

Multiple Alleles in Humans   Multiple alleles govern blood type   Ex.   ABO blood grouping system, where a single gene locus features multiple alleles- IA, IB, and i. Individuals carrying alleles for both A and B express both in the phenotype AB.

GenotypePhenotype (blood group) I A I A or I A iA I B I B, or I B iB IAIBIAIB AB iiO Multiple Alleles in Humans THE BLOOD TYPE

Sex determination:  ……white board

4. Sex - linked inheritance  1919 – T. Morgan – research on Drosophila – fruit flies;  Traits controlled by genes located on sex chromosomes – SEX-LINKED TRAITS. (X –linked trait, Y-link trait) (X –linked trait, Y-link trait)  EX. The allele for eye colors are carried on the X chromosome.

Sex-Linked Traits in Humans  Red-green color blindness - caused by two recessive alleles from X chromosome.  Hemophilia – X linked disorder.

5. Polygenic inheritance  The inheritance pattern of a trait that is controlled by two more genes.  Ex. Skin color, height in humans, cob length in corn.

6. Changes in Chromosome Numbers  It can affect autosomes – Down syndrome (Trisomy 21)  It can affect sex chromosomes – XYY or XXX or XXY