6 Patterns of Inheritance 1 Complete Dominance Mendelian

6 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

Polydactylism: • Complete dominance

Other more complex types of Inheritance • Roses have flowers of many different colors • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

2) Incomplete Dominance When one allele is not completely dominant over the other. • Heterozygous phenotype is in-between the two homozygous phenotypes. • Neither allele is dominant over the other, so they mix • New allele format

Snap dragons (four o-clocks) flower color varieties: red, white, and pink Red = F White = F’

Incomplete Dominance A cross between 2 pink four o’clock plants produces what phenotypic ratios?

3) Codominance Phenotypes of both homozygotes produced in heterozygote. • Neither allele is dominant over the other (both expressed). • Chickens that have white feathers, black feathers, and black and white feathers • New allele format: • B = black feathers • W = white feathers

WW BW BB

What type of inheretance? • MM’= Medium length legs • Hh= hitch hikers thumb • RB=red and black striped flower

4) Sex Linked: • In humans, 46 total chromosomes w/ 23 pairs • 22 of those are homologous = autosomal • 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? • With sex linked traits the gender will also affect the probability. • Some traits besides just sex determination are found on the X chromosomes. • Traits located on X chromosome = sexlinked (e. g. Color vision, hemophilia, baldness) • Boys need only 1 allele to express trait.

5) Multiple Allele: When genes can have more than 2 possible alleles for a characteristic in the gene pool. Any one individual can still only inherit 2 of those alleles however.

Different combinations of alleles result in the colors shown here. KEY 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 Could a chinchilla bunny have a himalayan baby if dad is full color? c = albino; no color; recessive to all other alleles

5) 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

6) Polygenic Inheritance: The inheritance pattern that is controlled by many (2 or more) genes When several genes reflect multiple additive contributions to a single phenotype. This results in traits that have a variety over a wide range. Ex: Height, Weight, Skin Pigment The greater the # of genes, the wider the range of variety.

6) 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?

6) Polygenic Inheritance: