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The Exceptions of Mendelian Genetics Incomplete Dominance Co-Dominance Multiple Alleles Multiple Genes.

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Presentation on theme: "The Exceptions of Mendelian Genetics Incomplete Dominance Co-Dominance Multiple Alleles Multiple Genes."— Presentation transcript:

1 The Exceptions of Mendelian Genetics Incomplete Dominance Co-Dominance Multiple Alleles Multiple Genes

2 Incomplete Dominance Mixtures of an alleles phenotype Example – Flower color in a snapdragon PhenotypeGenotype RedRR PinkRw Whiteww

3 w RR w w ww w R RRRR Incomplete Dominance Punnett Squares P – Red (RR) x White (ww) F1 – All Pink (Rw) F2 – Rw x Rw –Phenotypic Red : Pink : White 1 : 2 : 1 –Genotypic RR : Rw : ww 1 : 2 : 1 RR w w Rw R w Rw w

4 Co-Dominance Alleles that produce both phenotypes together. It is said that the alleles co-exist. Example – Chickens (Black / White / Checkered) Black and white co-exist in a Checkered chicken +=

5 BW B W BB W W W BB W W WW W B BBBB Co-Dominance Punnett Squares P – Black (BB) x White (WW) F1 – All Checkered (BW) F2 – BW x BW –Phenotypic Black : Checkered : White 1 : 2 : 1 –Genotypic BB : BB : WW 1 : 2 : 1 BW W

6 Multiple Alleles More than two “forms” (alleles) of a gene in a population Examples – Eye Color & Human Blood Types GenotypeBlood Type I A I A or I A I O A I B I B or I B I O B IAIBIAIB AB IOIOIOIO O

7 Multiple Genes A trait that is influenced by more than one gene Discovered by Bateson & Punnett Example – Chickens comb shape a. Single b. Rose c. Pea d. Walnut a b c d

8 X-Linked Traits Linkage of a hereditary trait associated with gender Primarily the X chromosome Examples – Color Blindness, Hemophilia & Baldness Signs of a X-linked Trait Trait occurs most in males Females are carriers of the trait Trait seems to jump generations

9 XX XcXc Y XcXc X X Y Y XcXc XcXc X Y XX Y X XXcXc XcXc X X-Linked Traits Punnett Squares P – XY x X c X F1 Generation –50% Females (1 is normal, 1 is a carrier) –50% Males (1 is color blind, 1 is normal) F2 – X c Y x XX –50% Females (Both are carriers) –50% Males (Both are normal) XX Y


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