RECAP Manx cat Mm MMMMm m mm 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 – A gene may be expressed at different stages of development – Eg cystic fibrosis, inability to recycle salt causing extra salty sweat

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

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

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) WT Rose R_pp Pea rrP_ Walnut R_P_ Single rrpp R is dominant to r P is dominant to p RP is codominant (walnut) rrpp single 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 Alleles of one gene mask the phenotype of alleles on another gene. In this case, rrpp masks a walnut comb

Epistasis on Flower 9:7 ratio is a modification of phenotypic but not genotypic Mendelian ratios. The C 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 F 1 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 CPCpcPcp CPCCPPCCPpCcPPCcPp CpCCPpCCppCcPpCcpp cPCcPPCcPpccPPccPp cpCcPpCcppccPpccpp In this case, white masks purple petal In this case, white masks purple petal

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

RatioDescriptionName(s) of Relationship (Used by Some Authors) 9:3:3:1Complete dominance at both gene pairs; new phenotypes result from interaction between dominant alleles, as well as from interaction between both homozygous recessives Not named because the ratio looks likeindependent assortment 9:4:3Complete dominance at both gene pairs; however, when 1 gene is homozygous recessive, it hides the phenotype of the other gene Recessive epistasis 9:7Complete dominance at both gene pairs; however, when either gene is homozygous recessive, it hides the effect of the other gene Duplicate recessive epistasis 12:3:1Complete dominance at both gene pairs; however, when one gene is dominant, it hides the phenotype of the other gene Dominant epistasis 15:1Complete dominance at both gene pairs; however, when either gene is dominant, it hides the effects of the other gene Duplicate dominant epistasis 13:3Complete dominance at both gene pairs; however, when eithergene is dominant, it hides the effects of the other gene Dominant and recessive epistasis 9:6:1Complete dominance at both gene pairs; however, when eithergene is dominant, it hides the effects of the other gene Duplicate interaction 7:6:3Complete dominance at one gene pair and partial dominance at the other; when homozygous recessive, the first gene is epistatic to the second gene No name 3:6:3:4Complete dominance at one gene pair and partial dominance at the other; when homozygous recessive, either gene hides the effects of the other gene; when both genes are homozygousrecessive, the second gene hides the effects of the first No name 11:5Complete dominance for both gene pairs only if both kinds ofdominant alleles are present; otherwise, the recessivephenotype appears No name

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

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. pleiotropicpleiotropic B. codominantcodominant C. epistaticepistatic D. lethallethal E. sex-linkedsex-linked