1. ( Modification of Mendelian ratios )
General Genetic
Bio 221 Lab 8
( Modification of Mendelian ratios )

2. Allelic or gene interactions
Modification of Mendelian ratios
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 environment affects 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 ) .

3. Type of non-mendelian
1- in complete ( partial , semi , intermediate ) dominance :
* The dominant characteristics in an allele influences , but does not overwhelm the heterozygote .
* 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 .

4. 2- Co - dominance ( Mosican dominance ) :
* Both allelic genes of a genetic trait are equally expressive , there is complete lack of dominance . When the heterozygotic 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 .

6. * EX:
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 .

7. Multiple alleles Which a population has more than two alleles in it .
EX: ABO blood groups in humans , in which there are 3 possible alleles A,B or IA and IB
( codominant ) , and i. type O blood is recessive .

8. Poly-genic 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
Genes that influence a trait indirectly . Such as , a dominant gene affects whether people can get early cataracts , but modifier genes determine how cataracts are likely to be . Often these modifier genes are located on different chromosome .

9. A - Mendelian Ratios and Lethal genes
B - Epistasis

10. A - 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

11. Kind of Lethal Genes 1- Recessive Lethal genes .
That occur in dominant or recessive traits but they do not cause death an organism carries 2 copies of lethal allel . The ratio 3:0 .
EX : Cystic fibrosis and 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 . Dominant traits can also be maintained in the population through mutations or the gene is less than 100% .
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 mutaion

12. 5- Conditional lethal genes
EX: 1- In enzyme ( glucose 6 phosphate dehydrogenase ) and 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 .
2- Temperature .

13. B - Epistasis
The effects of one gene are modified by one or several other genes .
Hypostatic : the phenotype altered or suppressed .
Epistatic : 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

14. 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 .
Color is recessive to no color at one allelic pair . At the first gene white colored squash is dominant to colored squash , and that gene code are W=white , w=colored . At the second gene yellow is dominant to green , and that gene code are G=yellow , g=green . The result in dihybrid is 3 phenotypes and produced 12:3:1 . The following table explanation for that ratio because the dominant W allele masks the effects of either the G or g allele .
Genotype
Phenotype
Enzymatic Activites
9 W_G_
White
Dominant white allele negates effect of G allele 12
3 W_gg
3 wwG_
yellow
Recessive color allel allows yellow allele expression 3
1 wwgg
Green
Recessive color allel allows green allele expression 1

15. 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 .
That effect by 2 enzyme A or B can produce a product from common precursor , only one dominant allele at either of 2 loci is required to generate the product .
* If pure wheat plant with colored kernal ( genotype = AABB) is crossed to plant with white kernels ( genotype =aabb ) and resulting F1 plants are selfed a modifiction of the dihybrid 9:3:3:1 ratio will be produced . The following table explanation for the ratio 15:1 because the genes can provide the wild type phenotype .
Genotype
Phenotype
Enzymatic Activites
9 A_B_
Colored Kernels
Functional enzymes from both genes 15
3 A_bb
Functional enzymes from A genes
3 aaB_
Functional enzymes from B genes
1 aabb
Non Functional enzymes from both genes 1

16. Black mice ( CCaa) X Albino(ccAA) mice
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 (a) masks the effect of dominant allele (B) .
When black mouse crossed to albino mouse , only agouti progeny were produced , but in F2 , 9 agouti , 3black and 4 albino (9:3:4) were produced .
Coat color in mouse is controlled by 2 dominant genes C and A .
In agouti color both the genes are dominant .
When only C is dominant , mouse color will be black .
When both recessive genes c and a are homozygous recessive , albino mice are produced .
Black mice ( CCaa) X Albino(ccAA) mice
F1 CcAa ( agouti)

17. Genotype Phenotype Enzymatic Activites
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 .
That effect by 2 genes are functional products from both for expression , then one recessive allelic pair would result in mutant phenotype .
* If pure line pea plant with colored flowers ( genotype = CCPP) is crossed to pure line , homozygous recessive plant with white flowers , the F1 plants will have colored flowers and CcPp genotype . The normal ratio from dihybrid is 9:3:3:1 . But Recessive duplicate Epistasis interaction between C and P genes will give modified 9:7 because both genes are required for correct phenotype , this epistatic interaction is called complementary gene action . The following table explanation for the ratio 15:1 because either the genes can provide the wild type phenotype .
Genotype
Phenotype
Enzymatic Activites
9 C_P_
Colored colored : anthocyanin produced
Functional enzymes from both genes 9
3 C_pp
Flowes white : no anthocyanin produced
p enzyme non-functional 7
3 ccP_
c enzyme non-functional
1 ccpp
C and p enzymes non-functional

18. Experimental
Separate the drosophelia (F2 ) From second Low and record the changes for chi –square ++ e vg Vg
Male
Female
Total
/D . S
Obs.
2- e
3- vg
4- vg-e