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
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