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Incomplete & Codominance Genetics Biology 30 Mrs. S. Pipke-Painchaud Reviewing All photos from: http://www.naturalselectionreptiles.com/Genetics.html Incomplete Dominance • (a.k.a. partial dominance or blending) • occurs when both alleles contribute to a trait that is not like either parent. • this condition is only seen in the heterozygous individual – ex.. Snap Dragons or Four O’Clocks or Morning Glory or Primrose (Flowers) – Curly (homozygous) or straight (homozygous), but if you are heterozygous you have wavy hair. Example: Snap Dragons Parents: Red X White W = red w = white Parents are both true breeding red and white. WW X ww W http://www.usask.ca/biology/genetics/extensions/ snapdragon.jpg W Genotype: All Ww w Ww Ww Phenotype: All Pink w Ww Ww F1 x F1 Cross http://www.visionle arning.com/library/ modules/mid129/Im age/VLObject3228050216120240.jpg Ww X Ww W w W WW Ww w Ww ww Remember: W = red w = white Ww = pink Genotypic Ratio: 1WW: 2 Ww: 1ww Phenotypic ratio: 1 Red: 2 Pink: 1 White ***NOTE: Because there is no dominance in the heterozygote the phenotypic ratio is identical to the genotypic ratio**** • http://courses.bio.psu.edu/fall2 005/biol110/tutorials/tutorial5_f iles/figure_14_9.gif http://library.thinkquest.org/2046 5/media/flowers.gif How the coloring works . . . • WW – have enough pigment to be red • ww - flowers don’t have any pigment = no color • Ww – only have enough pigment to be pink Codominance • the two dominant genes are expressed at the same time • both traits appear in the heterozygous individual at the same time – ex.. Roan (Red or Blue) coat color in horses and cattle – Chestnut and White color in horses are both dominant traits; the heterozygous individual is a palomino (golden). Blue Roan Example: http://www.virginiacowboy.com/sitebuilder/images /DSC_0040-803x536.jpg Red Roan Example: Coat Color in Horses • C= Color gene • CR CR = Red CW CW = White CR CW = Red Roan If you cross a true breeding Red horse with a true breeding white horse, what ratios will you get? Genotypic Ratio: All CR CW Phenotypic Ratio: All Red Roan CR CR CW CR CW CR CW CW CR CW CR CW Example: MN Blood Group • MN blood group – is characterized by a certain type of glycoprotein on the surface of the RBCs. • • • • • There are two forms: M and N Designate is L L ML M = M LNLN = N LMLN = MN type MN Blood Group • • • LMLM = M LNLN = N LMLN = MN type What types of offspring would be produced from a cross of a homozygous M type with an MN type? Parents: LMLM X LMLN Genotypic Ratio: 1 LMLM : 1 LMLN LM Phenotypic Ratio: 1 M blood type: 1 MN blood type LM LM LMLM LMLM LN LMLN LMLN Resource Sites