Patterns of Inheritance 1 Complete Dominance Mendelian Dominance

Patterns of Inheritance

1) Complete Dominance • (Mendelian Dominance) Homozygous dominant and heterozygous individual has same phenotype. • TT = tall ; Tt = tall • Results in only 2 variations

Other types of Inheritance • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

Incomplete Dominance • When one allele is not completely dominant over the other. • Heterozygous phenotype is between the two homozygous phenotypes. FF FF’ F’F’

Incomplete Dominance • A cross between red (RR) and white (R’R’) four o’clock plants produces pink -colored flowers (RR’). F F F’ FF’ FF’

Codominance • Phenotypes of both homozygotes produced in heterozygote. • Neither allele is dominant over the other (both expressed). • Chickens have white feathers, black feathers, and black and white feathers • New allele format: BB = Black feathers (homo) WW = white feathers (homo) BW = Black & White feathers (hetero)

4) Sex Linked: • In humans, 46 total chromosomes w/ 23 pairs • 22 of those are homologous = autosomes • 1 pair are the sex chromosomes (different for males and females)

4) Sex Linked: • What are the chances of getting a boy to a girl? • Some traits besides just sex determination are found on the sex chromosomes. • Traits located on X chromosome • Boys need only 1 allele to express trait. • Colorblind

5) Polygenic Inheritance: • Several genes reflect multiple additive contributions to a phenotype. • These traits have a variety over a wide range. • Ex: Height, Weight, Skin Pigment • The greater the # of genes, the wider the range of variety.

5) Polygenic Inheritance: • Ex: 3 genes control the mass of bristle worms, and every dominant allele contributes 1 g. • How many alleles/gene? • How many alleles are there for mass in bristle worms? • Homozygous skinny = 2 g (genotype? ) • How much mass would the fattest bristle worm have? • The mass of most bristle worms would be?

5) Polygenic Inheritance:

6) Multiple Allele: • When genes can have more than 2 possible alleles for a characteristic in the population’s gene pool. • Any individual organism still inherits only two alleles (one from each parent)

• Different combinations of alleles result in the KEY colors shown here. C= full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele chch ch ch AIbino: Chinchilla: Himalayan: cc CC, ccchhcc, h. Cc , c or c, hhor cch c Full color: , Cc , or Cc c = albino; no color; recessive to all other alleles

6) Multiple Allele: • Ex: Many codominant alleles in human blood types. • The gene encodes an enzyme that adds sugar molecules to the plasma membrane of red blood cells. Act as recognizing markers for the antibodies for the immune system. • Gene is designated I and has 3 possible alleles. • IA, IB, and i • IA and IB are codominant. • Both I’s are completely dominant over i. Figure out how to get the A, B, AB, and O blood types