Gene Interactions

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Published on March 11, 2012

Author: sonudin

Source: authorstream.com

GENE EXPRESSION: GENE EXPRESSION Gene-gene interaction Gene-environment interaction Gene-gene interactions will be selected from: complementary, supplementary and collaboration, polygenes . Gene Interactions: Gene Interactions With the help of lot of experiments it was found that most of the characters of living organisms are controlled / influenced / governed by a collaboration of several different genes. This condition where a single character is governed by two or more genes and every gene affect the expression of other genes involved (means these genes affect each others expression) is known as gene interaction. In simple way we could say that, in gene interaction, expression of one gene depends on expression (presence or absence) of another gene. As we know, gene interactions may involve two or more pairs of genes. But all the gene interactions we have described below have the two pairs of non-allelic genes, affecting the phenotypic expression of same character. These interactions produce modified dihybrid ratios. Gene Interactions Types : Gene Interactions Types Gene interactions can be classified as Allelic gene interaction Non-allelic gene interaction Non-allelic gene interaction Expression of character is produced by interaction between two or more genes. The interactions we have listed below, as inter and intra allelic are of this type. Inter-allelic Intra-allelic Inter-allelic Without modification of normal F 2 ratio With modification of normal F 2 ratio Such kinds of interactions modify the normal F 2 ratio (9:3:3:1). Various types of such interactions are as below. Gene Interactions ratios: Gene Interactions ratios Gene Interaction F 2 Ratio Test Cross Ratio Epistasis 12:3:1 2:1:1 Complementary Gene Interaction 9:7 1:3 Supplementary Gene Interaction 9:3:4 1:1:2 Duplicate Factor 15:1 3:1 Inhibitory Factor 13:3 1:3 Polymerism or Additive Factor 9:6:1 1:2:1 Gene Interactions ratios: Gene Interactions ratios Epistasis (12:3:1): Involves two pairs of non-allelic genes Both the dominant genes affect the same character. One of them, when present alone or along with other dominant gene expresses itself . The other gene expresses itself only when it is alone. The recessive forms of both the genes give rise to different phenotype. The phenomenon of masking of effect of one dominant gene by the other gene is called as “ epistasis ”, and hence the interaction is named as epistasis . Cross between F 1 F 2 WWYY X wwyy white X green WwYy white 13 white : 3 yellow: 1 green Gene Interactions ratios: Gene Interactions ratios Complementary Gene Interaction (9:7) Involves two pairs of non-allelic genes. When dominant forms of both the genes involved in complementary gene interaction are alone have same phenotypic expression But, if they are present in combination, yield different phenotypic effect. Flower color in garden pea follow this type of gene interaction. Supplementary Gene Interaction (9:3:4) Involves two pairs of non-allelic genes. Affect the same character. One of the dominant gene has visible effect itself . Second dominant gene expresses itself when supplemented by the other dominant gene of a pair Coat color (black, albino and agouti) of mice follows supplementary gene interaction. Cross between F 1 F 2 WWcc X wwCC white X white WwCc purple 9 purple : 7 white Cross between F 1 F 2 CCaa X ccAA black X albino CcAa agouti 9 agouti : 3 black: 4albino Gene Interactions Epistasis: Gene Interactions Epistasis Epistasis is when one gene affects the expression of another gene Two or more separate genes ( not separate alleles at one genetic locus ) interact to control a phenotypic character. If one gene locus prevents the expression of a second gene, the first locus is epistatic to the second, and the second is hypostatic to the first. There are no new phenotypes produced by this type of gene interaction. Gene Interactions Epistasis: The alleles that are masking the effect are called epistatic alleles The alleles whose effect is being masked are called the hypostatic alleles . Types of Epistasis : RECESSIVE EPISTASIS : Recessive alleles of one gene locus ( aa ) mask the trait of alleles of another gene locus (BB, Bb,bb ) 9:3:4 DOMINANT EPISTASIS: When out of two genes the dominant allele (A) of one gene masked the trait of another gene (B) and express itself 12:3:1 Gene Interactions Epistasis PowerPoint Presentation: RECESSIVE EPISTASIS : Recessive alleles of one gene locus ( aa ) mask the trait of alleles of another gene locus (BB, Bb,bb ) Allele B, b express only when Epistatic locus has AA or Aa Ratio 9:3:4 Gene Interactions recessive Epistasis Epistatic alleles Hypostatic alleles PHENOTYPE aa BB, Bb, bb a AA, Aa BB, Bb B AA, Aa bb b PowerPoint Presentation: Gene Interactions recessive Epistasis Coat color in mice Wt coat color is agouti - A (dominant to black); Nonagouti (black) coat color - a Pigmentation expression - B (dominant to albino); No pigmentation (albino) - b If individual is bb, then is albino regardless of allele at a locus - due to gene interaction. Coat color in mice: Coat color in mice Agouti Markings A- hair made with bands of black pigment and yellow pigment. Aa hair all black. PowerPoint Presentation: Coat color example of epistasis When a homozygous black ( CCaa ) is crossed with homozygous albino ( ccAA ) in F1 all agouti offspring occurs. Determine the self pollinated F2 progeny if cc is recessive epistatic . Parents Phenotype Black Albino Parent Genotype CCaa ccAA P1 Gametes Ca cA F1 CcAa (Agouti) selfing CcAa CcAa Gametes CA, Ca, cA , ca PowerPoint Presentation: Coat color example of epistasis F2 Generation Male Female CA Ca cA ca CA CCAA Agouti CCAa Agouti CcAA Agouti CcAa Agouti Ca CCAa Agouti CCaa Black CcAa Agouti cCaa Black cA CcAA Agouti CcAa Agouti ccAA Albino ccAa Albino ca CcAa Agouti Ccaa Black ccAa Albino ccaa Albino 9:3:4 (F2 ratio) PowerPoint Presentation: Coat color example of epistasis When a homozygous black (WWGG) is crossed with homozygous albino ( wwgg ) in F1 all agouti offspring occurs. Determine the self pollinated F2 progeny if cc is recessive epistatic . Parents Phenotype White White Parent Genotype WWGG wwgg P1 Gametes WG wg F1 WwGg (Green) selfing WwGg WwGg Gametes WG, Wg , wG , wg PowerPoint Presentation: Coat color example of epistasis F2 Generation Male Female WG Wg wG wg WG CCAA Agouti CCAa Agouti CcAA Agouti CcAa Agouti Wg CCAa Agouti CCaa Black CcAa Agouti cCaa Black cA CcAA Agouti CcAa Agouti ccAA Albino ccAa Albino ca CcAa Agouti Ccaa Black ccAa Albino ccaa Albino 9:3:4 (F2 ratio) PowerPoint Presentation: AABB (agouti) x aabb (albino) AaBb (all agouti) AaBb x AaBb A-B- agouti 9/16 9/16 A-bb albino 3/16 4/16 aaB - black 3/16 3/16 aabb albino 1/16 Genotype Phenotype F2 ratio Final phenotypic ratio Coat color example of epistasis Due to gene interaction, we see a 9:3:4 F2 ratio. The b locus is epistatic to the a locus. PowerPoint Presentation: DOMINANT EPISTASIS: When the dominant allele (A) of one gene masked the trait of another gene (B) and express itself 12:3:1 Gene Interactions dominant Epistasis Epistatic alleles Hypostatic alleles PHENOTYPE AA, Aa BB, Bb, bb A aa BB, Bb B aa bb b Dominant Epistasis: Dominant Epistasis Let’s have a look at dominant epistasis… Squash fruit color is controlled by two genes. Gene 1 is represented by a W Gene 2 is represented by a G Squash Fruit Color: Squash Fruit Color Genotypes and Phenotypes: Ww / Gg white Ww / gg white ww / Gg green ww / gg yellow PowerPoint Presentation: Squash Colour Progeny Male Female WG Wg wG wg WG WWGG White WWGg White WwGG White WwGg White Wg WWGg White WWgg White WwGg White Wwgg White wG WwGG White WwGg White wwGG Green wwGg Green wg WwGg White Wwgg White wwGg Green wwgg Yellow 12:3:1 (F2 ratio) Parent Genotype WwGg WwGg Gametes WG / Wg / wG / wg WG / Wg / wG / wg Squash Fruit Color: Squash Fruit Color Which allele is epistatic in squash color? How do you know? The dominant W allele is epistatic Because every time a dominant W allele shows up in a squash genotype, the squash fruit color is white. Try this cross….: Try this cross…. Cross a green squash ( wwGg ) with a white squash ( Wwgg ). Parents Phenotype Green Squash White Squash Parent Genotype wwGg Wwgg Gametes wG wg Wg wg PowerPoint Presentation: Squash Colour Progeny Male Female wG wg wG wg Wg WwGg White Wwgg White WwGg White Wwgg White wg wwGg Green wwgg Yellow wwGg Green wwgg Yellow Wg WwGg White Wwgg White wwGg White Wwgg White wg wwGg Green wwgg Yellow wwGg Green wwgg Yellow 8:4:4 (F2 ratio) Parent Genotype wwGg Wwgg Gametes wG wg Wg wg Wwgg x wwGg: Wwgg x wwGg Gametes : Wg wg wG wg Male Female Wg Wg wG wg Wg WWgg White WWgg White WwGg White Wwgg White Wg WWgg White WWgg White WwGg White Wwgg White wG WwGg White WwGg White wwGG Green wwGg Green wg Wwgg White Wwgg White wwGg Green wwgg Yellow 12:3:1 (F2 ratio) interaction of Genes: interaction of Genes Epistasis DOMINANT EPISTASIS - 12:3:1 RECESSIVE EPISTASIS - 9:3:4 Gene Interactions: Gene Interactions e.g. Complementary genes (Duplicate recessive) Lethal genes supplementary genes and collaboration . Complementary Genes: Complementary Genes When at least one dominant gene at two loci must be present for the development of a characteristic. Both dominant alleles when present together they complement each other and develop a trait Complementary Genes: Complementary Genes Types of Complementation: DOMINANT COMPLEMENTARY GENES: When both dominant alleles present together, they complement each other and produce different phenotype (9:7) RECESSIVE COMPLEMENTARY GENES: If both dominant alleles of both loci produce the same phenotype without cumulative effect. Both recessive aa & bb are necessary for phenotype (15:1) dominant Complementary Genes: dominant Complementary Genes When both dominant alleles present together, they complement each other and produce different phenotype (9:7) Loci 1 alleles Loci 2 alleles PHENOTYPE aa BB, Bb, bb No pheno . AA, Aa , aa BB, Bb No pheno . AA, Aa bb Phenotype Dominant Complementary Genes: e.g. purple flowers on sweet peas require the presence of C and P . The genotypes for purple flowers are CCPP , CCPp , CcPP or CcPp (also written as C-P- ). Any other genotype produces white flowers. Dominant Complementary Genes dominant Complementary Genes: dominant Complementary Genes The dominant allele C & P independently produces white coloured flowers in the Maize. When both of them present together they produce purple coloured flowers. Determine the phenotypic F2 ratio in F1 selfed progeny of the following parents – CCpp X ccPP (Both white) dominant Complementary Genes: dominant Complementary Genes CCpp X ccPP (Both white) Gametes Cp cP F1 CcPp (Purple) Male Female CP Cp cP cp CP CCPP CCPp CcPP CcPp Cp CCPp CCpp CcPp Ccpp cP CcPP CcPp ccPP ccPp cp CcPp Ccpp ccPp ccpp F2 ratio - 9 (Purple) : 7 (white) PowerPoint Presentation: There are only two possible phenotypes. 9: 7 ratio means both functional genes are required to produce phenotype dominant Complementary Genes recessive Complementary Genes: recessive Complementary Genes If both dominant alleles of both loci produce the same phenotype without cumulative effect. Both recessive aa & bb are necessary for phenotype 15:1 Loci 1 alleles Loci 2 alleles PHENOTYPE aa BB, Bb, bb Complement aa AA, Aa BB, Bb BB, Bb Pheno . of either parent (same) AA, Aa bb recessive Complementary Genes: recessive Complementary Genes The dominant allele C & P independently produces triangular seed capsules in the shephard’s pulse. When both of recessive alleles c & p present together they produce top shaped seeds. Determine the phenotypic F2 ratio in F1 selfed progeny of the following parents – CCPP (Triangular) X ccpp (Top) dominant Complementary Genes: dominant Complementary Genes CCPP (Triangular) X ccpp (Top) Gametes CP cp F1 CcPp (Triangular) Male Female CP Cp cP cp CP CCPP CCPp CcPP CcPp Cp CCPp CCpp CcPp Ccpp cP CcPP CcPp ccPP ccPp cp CcPp Ccpp ccPp ccpp F2 ratio - 15 (Purple) : 1 (white) interaction of Genes: interaction of Genes Complementary Interactions DOMINANT COMPLEMENTARY GENES - 9:7 RECESSIVE COMPLEMENTARY GENES - 15:1 lethal Genes - In Human Beings : lethal Genes - In Human Beings Congenital ichthyosis Recessive Lethal Crusted leathery skin Deep fissures Homozygous condition of recessive alleles lethal Genes: lethal Genes Modification of Monohybrid ratio (3:1) Presence of allele who is drastic to cause death Ratio alters 2:1 (1 Dies due to lethal Gene) Types: Zygotic Gametic Gametophytic interaction of Genes: interaction of Genes Epistasis DOMINANT EPISTASIS - 12:3:1 RECESSIVE EPISTASIS - 9:3:4 Complementary Interactions DOMINANT COMPLEMENTARY GENES - 9:7 RECESSIVE COMPLEMENTARY GENES - 15:1 Lethal Genes - 2:1 lethal Genes: lethal Genes Modification of Monohybrid ratio (3:1) In Snapdragon plant CC - Green Cc - Golden cc - White White plants dies CC Cc Cc cc lethal Genes - In Human Beings : lethal Genes - In Human Beings Congenital ichthyosis Recessive Lethal Crusted leathery skin Deep fissures Homozygous condition of recessive alleles lethal Genes - In Human Beings : lethal Genes - In Human Beings Congenital ichthyosis lethal Genes - In Human Beings : lethal Genes - In Human Beings Amaurotic idiocy Recessive Lethal loss of eye site (5-7) Mental degeneration Death Homozygous condition of recessive alleles Tay –Sachs disease ( Warren Tay , 1881) The enzyme involved in Tay -Sachs is called hexosaminidase A . Its absence allows a lipid called GM 2 ganglioside to build up in the brain, destroying the nerve cells. lethal Genes - In Human Beings : lethal Genes - In Human Beings Sickle cell anemia Codominant Lethal in homozygous condition Erythrocytes sickled Blocks capillaries Carrying capacity loss Death lethal Genes - In Human Beings : lethal Genes - In Human Beings Sickle cell anemia Codominant Lethal in homozygous condition Erythrocytes sickled Blocks capillaries Carrying capacity loss Death lethal Genes - In Human Beings : lethal Genes - In Human Beings Sickle cell anemia lethal Genes - In Human Beings : lethal Genes - In Human Beings Sickle cell anemia Supplementary Genes: Supplementary Genes British geneticists William Bateson and R.C. Punnett conducted research showing that the shape of the comb in chickens was caused by the interaction between two different genes. Bateson and Punnett were aware of the fact that different varieties of chickens possess distinctive combs. (1875-1967) (1861-1926) Supplementary Genes: Supplementary Genes 2 pair of gene (R & P) interacting to produce comb colour and size During inheritance of comb in chicken they do not determine presence or absence of trait They modify character determined by basic gene Therefore they are supplementary or Modifying genes. Supplementary Genes: Supplementary Genes For instance, Wyandottes have a "rose" comb, Brahmas have a "pea" comb, and Leghorns have a "single" comb. When Bateson and Punnett crossed a Wynadotte chicken with a Brahma chicken, all of the F 1 progeny had a new type of comb, which the duo termed a "walnut" comb. Supplementary Genes: Supplementary Genes Rose ( RRpp ) Pea ( rrPP ) Wanlut ( RrPp ) Supplementary Genes: Supplementary Genes Rose ( RRpp ) 3 RRpp Rrpp R dominance over r Wanlut ( RrPp ) 9 RRPP RRPp RrPP RrPp R & P supplementing Pea ( rrPP ) 3 rrPP rrPp P dominance over p Single ( rrpp ) 1 Recessiveness of rr & pp interaction of Genes: interaction of Genes Epistasis DOMINANT EPISTASIS - 12:3:1 RECESSIVE EPISTASIS - 9:3:4 Complementary Interactions DOMINANT COMPLEMENTARY GENES - 9:7 RECESSIVE COMPLEMENTARY GENES - 15:1 Lethal Genes - 2:1 Supplementary – 9:3:3:1 Polygenes: Polygenes A single phenotype may be influenced by more than one gene, e.g. body height and skin colour A continuum of phenotypes exists PowerPoint Presentation: aabb = white skin Aabb, aaBb = light skin AAbb, AaBb, aaBB = medium kin AaBB, AABb = dark skin AABB = black skin Gene-Environment Interactions: Gene-Environment Interactions Gene-environment interactions include examples of determination of phenotype by environment e.g. determination of sex in crocodile hatchlings by temperature (cool -  female, warm  male) . Environmental Effects on Phenotype: Environmental Effects on Phenotype Genes determine the limits of a range of possible phenotypes. Environment influences the extent to which the genotype is realised. Two mechanisms: -direct effects -indirect effects Environmental Effects on Phenotype: Environmental Effects on Phenotype Direct effects are due to a lack of raw materials, energy or other essential growth factors. Scurvy is a deficiency disease. PowerPoint Presentation: Indirect effects are adaptive responses and a factor in the environment usually changes the activity of genes (turns them off or on). Examples of Environmental Effects on Phenotype : Examples of Environmental Effects on Phenotype Photoperiod may determine whether a shoot produces leaves or a flower. Daylength determines coat colour in Arctic mammals. E. coli only produce lactase when lactose sugar is present.

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