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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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Recap

RECAP

  • Manx cat

Manx

Death

Normal


Pleiotropy

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


5 gene interactions

5- GENE INTERACTIONS

Compiled by

Siti Sarah Jumali

Level 3 Room 14

Ext 2123


Polygene interactions

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


Epistasis

EPISTASIS

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


Epistasis1

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


Chicken comb recessive epistasis

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


Epistasis on chicken comb

Epistasis on Chicken Comb

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


Epistasis on flower

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.


9 7 phenotypic ratio

9:7 phenotypic ratio

  • In this case, white masks purple petal


9 3 4 ratio

9:3:4 ratio

  • Agouti x Agouti

    • BbCc x BbCc

    • Brown agouti & albino mask agouti

    • c epistatic to B;

      b epistatic to C


Recap

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


Question

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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