Presentation on theme: "General Genetic. Most traits are non-mendelian, meaning they do not follow the rules of mendelian traits. Almost all traits in humans are non-mendelian."— Presentation transcript:
Most traits are non-mendelian, meaning they do not follow the rules of mendelian traits. Almost all traits in humans are non-mendelian. The trait is determined by : 1- more than one gene. 2- or the environmental effects of the trait. Allelic or gene interactions 1- The gene in an organism can interact in many different ways. 2- The effect of dominant allele is diluted or modified so that the phenotypic expression of the concerned trait in a hybrid (Heterozygous ) is distinguishable from both parental types ( Homozygous )
Type of non-mendelian 1- in complete ( partial, semi, intermediate ) dominance : A type of inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype (expressed physical trait). and character is intermediate between the parentsallelephenotype * Phenotype and genotype ratios in F2 generation are 1:2:1. * EX : Red shaded chrysanthemum breed with white shaded chrysanthemum, the resulting is pink. The mixture of colors shows incomplete dominance between colors.
2- Co - dominance ( Mosaic dominance ) : * Both allelic genes of a genetic trait are equally expressive, there is complete lack of dominance. When the heterozygote organism shows the characteristics of two dominant alleles. * Phenotype and genotype ratios in F2 generation are 1:2:1. * EX: 1- White cat and black cat generate offspring that the dominant alleles share dominance. 2- Red and white coat colors in short-horn cattle expressions ( Phenotype), and they are homozygous dominant and homozygous recessive genotypes. The hybrids exhibit a roan coat color is intermediate
With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits. With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. Incomplete VS Codominance
* EX: ( codominace) 3- The AB blood group is due to co-dominance. AB group is controlled by the genes A and B. The A and B are equally dominant. A produces antigen A and B produces antigen B.
4 - Sickle cell anemia is recessive disease. In heterozygous which have abnormal red blood cells under some conditions. Incomplete dominance example
Multiple alleles -Which a population has more than two alleles in it. -Multiple alleles increases the number of different phenotypes. -Multiple alleles can be dominant, recessive or co- dominant to each other. EX: ABO blood groups in humans, in which there are 3 possible alleles A,B or IA and IB ( co dominant ), and i. type O blood is recessive.
Polygenic inheritance More than one gene affecting a trait. Most traits in humans are polygenic, such as weight, height. IQ, personality,( skin color is environmental determined and determined by 5 genes, each with 2 alleles giving 9 phenotypes. ) Modifier genes A gene that alters the phenotypic expression of another gene.
Mendelian Ratios and Lethal genes In 1905, Lucien Cuenot observed unusual patterns when studying inheritance of a coat color gene in mice. After mating 2 yellow mice, observed that the offspring never showed a normal 3:1 phenotype but observed 2:1, with 2 yellow mice and one non-yellow mice. This is lethal genes cause the death of the organisms that carry them. Sometimes, death is not immediate it may take yeas depending on the gene. Kind of Lethal Genes : 1- Recessive Lethal genes. The ratio 3:0. EX : Cystic fibrosis and Sickle cell anemia 2- Dominant lethal genes. The ratio 2:1. EX: Huntington disease 3- Semi or Sub Lethal genes. EX : Hemophilia 4- Synthetic Lethal genes. 5- Conditional lethal genes. EX: favism allele
Kind of Lethal Genes 1- Recessive Lethal genes. That occur in dominant or recessive traits but they do not cause death unless an organism carries 2 copies of lethal allel. The ratio 3:0. EX : Sickle cell anemia. 2- Dominant lethal genes. Are expressed in both homozygotes and heterozygotes. The ratio 2:1 EX: Huntington disease, a neurological disorder in humans ( chromosome 4 ). 3- Semi or Sub Lethal genes. The allele responsible for hemophilia is carried on the X chromosome, affected mainly in males, and they inherit the allele from their mothers. Hemophilia = is affected in individual bleed as longer period of time until clotting occurs, this means that normally minor wounds can be fatal in a person. 4- Synthetic Lethal genes. Some mutations are only lethal when paired with second mutation
5- Conditional lethal genes EX: favism allele that common among people of Mediterranean, African and Southeast Asian. The disease was named because when affected individuals eat fava beans, they develop hemolytic anemia, a condition in which red blood cells break apart and block blood vessels. But that disease is resistant to malaria because it is difficult for malaria to multiply in cells with deficient a mount of glucose 6 phosphate dehydrogenase.
Epistasis The effects of one gene are modified by one or several other genes. Hypo-static : is one whose phenotype is masked by the expression of an allele at a separate locus, in an epistasis eventphenotypealleleepistasis Epi-static : The gene whose phenotype is expressed. Epistasis can be contrasted with dominance which is an interaction between alleles at the same gene locus. The interaction between two or more genes to control a single phenotype and identify and recognize the 9:3:3:1 that results of crossing 2 dihybrids produced a modified mendelian. Kind of Epistasis : 1- Dominant Epistasis : (12:3:1 ) from ( 9: 3 :3 :1 ) EX: Fruit color in squash 2- Dominant duplicate Epistasis : (15:1 ) from ( 9: 3:3 :1 ) EX: Kernel Color in wheat 3- Recessive Epistasis: (9:4:3 ) from ( 9: 3: 3 :1 ) EX: mice coat color 4- Recessive duplicate Epistasis : (9:7) from ( 9: 3:3 :1 ) EX: Flower Color in sweet pea
Kind of Epistasis : 1- Dominant Epistasis. * Definition :Complete dominance at both gene pairs ; when one gene is dominant, it hides the effects of other gene. And the ratio is 12:3: 1 * EX: Fruit color in squash. Genotype Phenotype Enzymatic Activites 9 W_G_WhiteDominant white allele negates effect of G allele 12 3 W_ggWhiteDominant white allele negates effect of G allele 3 wwG_yellowRecessive color allel allows yellow allele expression3 1 wwggGreenRecessive color allel allows green allele expression 1
1- Dominant Epistasis : (12:3:1 ) from ( 9: 3 :3 :1 ) EX: Fruit color in squash when one gene is dominant gene 1= ( white dominant (WW), colored (ww) ). gene 2= ( yellow is dominant (YY), green ( yy ) ). ♂/♀ WYWywYwy WYWWYYWWYyWwYYWwY y WyWWYyWWyyWwYyWwy y wYWwYYWwYywwYYwwY y wyWwYyWwyywwYywwyy The effect of dominant gene ’Y’ is masked by the dominant gene ’W’ (epistatic gene) P WWYY X wwyy (white) ↓ (green) F1 WwYy (white) (selfed) F2 White:Yellow:Gree n 12 : 3 : 1
2- Dominant duplicate Epistasis. * Definition :Complete dominance at both gene pairs ; when either gene is dominant, it hides the effects of other gene. And the ratio is 15 : 1 * EX: Kernel Color in wheat. Genotype Phenotype Enzymatic Activites 9 A_B_Colored KernelsFunctional enzymes from both genes 15 3 A_bbColored KernelsFunctional enzymes from A genes 3 aaB_Colored KernelsFunctional enzymes from B genes 1 aabbWhite KernelsNon Functional enzymes from both genes 1
Dominant duplicate Epistasis : (15:1 ) from ( 9: 3:3 :1 ) EX: Kernel Color in wheat when either gene is dominant Gene A = Enzyme AA Gene B = Enzyme BB AABBaabb AaBb AABB 9 الجينين يعملان AAbb 3 يعمل A aaBB 3 يعمل B aabb 1 لايعمل 151
3- Recessive Epistasis. *Definition: Complete dominance at both gene pairs ; when one gene is homozygous recessive, it hides the effects of other gene. And the ratio is 9:4:3 * EX: mice coat color. in some casses recessive allele c masks the effect of dominant allele (B). When black mouse crossed to albino mouse, only black progeny were produced, but in F2, 9 black, 3 cream and 4 albino (9:3:4) were produced. Coat color in mouse is controlled by 2 dominant genes B and C When B is dominant, mouse color will be black. When both recessive genes b and c are homozygous recessive, albino mice are produced. In this case when c is homozygous it masked the effect of the B gene. Black mice ( BBCC) X Albino (bbcc) mice F1 BbCc( black)
Recessive Epistasis: (9:4:3 ) from ( 9: 3: 3 :1 ) EX: mice coat color when one gene is homozygous recessive
4- Recessive duplicate Epistasis. * Definition : Complete dominance at both gene pairs ; when either gene is homozygous recessive, it hides the effects of other gene. And the ratio is 9: 7 * EX: Flower Color in sweet pea.. The following table explanation for the ratio 9:7 because either the genes can provide the wild type phenotype. Genotype Phenotype Enzymatic Activites 9 C_P_Colored : anthocyanin producedFunctional enzymes from both genes 9 3 C_ppFlowes white : no anthocyanin produced p enzyme non-functional7 3 ccP_Flowes white : no anthocyanin producedc enzyme non-functional 1 ccppFlowes white : no anthocyanin producedC and p enzymes non-functional
Recessive duplicate Epistasis : (9:7) from ( 9: 3:3 :1 ) EX: Flower Color in sweet pea ; when either gene is homozygous recessive Gene1 =C Gene2=P CCPP Colored ccpp white CcPp CCPP عمل كلا الجينين 9 CCpp لايعمل انزيم P 3 ccPP لايعمل انزيم C 3 ccpp لايعمل 1 9 Colored 7 White