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RECAP. Manx cat. Manx Death Normal. PLEIOTROPY. Is multiple effects of a single gene on the phenotype Occurs for several reasons suppression of single gene can affect cell function in more than one way A gene may be expressed in different cell types in a multicellular organism

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  1. RECAP • Manx cat Manx Death Normal

  2. PLEIOTROPY • Is multiple effects of a single gene on the phenotype • Occurs for several reasons • suppression of single gene can affect cell function in more than one way • A gene may be expressed in different cell types in a multicellular organism • A gene may be expressed at different stages of development • Eg cystic fibrosis, inability to recycle salt causing extra salty sweat

  3. 5- GENE INTERACTIONS Compiled by Siti Sarah Jumali Level 3 Room 14 Ext 2123

  4. Polygene interactions • Mendel studied one gene for height but he did not realize that there are other genes that also affect height • i.e. • Tall strain KK LL MM NN OO PP QQ RR SS TT • Dwarf strain KK LL MM NN OO PP QQ RR SS tt

  5. EPISTASIS • An inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene

  6. EPISTASIS • Occurs when: gene at one locus affects the expression of an allele at a different locus b. • eg: fur color in mice • 1) B is allele for black fur 2) b is allele for brown fur 3) BUT, must have allele C at a different locus to have colored fur 4) if different locus has cc, then fur is colorless even if B or b is present 5) see what happens when BbCc mouse is crossed with BbCc mouse (a) expect a (9:3:3:1 ratio) (b) get a 9:3:4

  7. Chicken comb (recessive epistasis) Rose R_pp Pea rrP_ Walnut R_P_ Single rrpp WT R is dominant to r P is dominant to p RP is codominant (walnut) rrpp single comb

  8. Epistasis on Chicken Comb • Alleles of one gene mask the phenotype of alleles on another gene. In this case, rrpp masks a walnut comb

  9. Epistasis on Flower • 9:7 ratio is a modification of phenotypic but not genotypic Mendelian ratios. • TheC and P genes independently assort, the presence of a recessive genotype at one locus (i.e., cc or pp) masks the effects of the alleles at the other locus. • There are 9 combinations of alleles in the F1 generation that feature at least 1 dominant C and 1 dominant P allele, which would yield a purple flower phenotype • Conversely, there are seven combinations that result in either a cc or a pp, which would yield the white flower phenotype-hence, the 9:7 ratio of purple to white flowers.

  10. 9:7 phenotypic ratio • In this case, white masks purple petal

  11. 9:3:4 ratio • Agouti x Agouti • BbCc x BbCc • Brown agouti & albino mask agouti • c epistatic to B; b epistatic to C

  12. All of these are also called as gene modifier effect by other geneticists

  13. Question • Manx cats are heterozygous for a dominant mutation that results in no tails (or very short tails), large hind legs, and a distinctive gait. The mating of two Manx cats yields two Manx kittens for each normal, long-tailed kitten, rather than three-to-one as would be predicted from Mendelian genetics. Therefore, the mutation causing the Manx cat phenotype is likely a(n) __________ allele. • A. pleiotropic • B. codominant • C. epistatic • D. lethal • E. sex-linked

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