Codominance vs Incomplete Dominance. People often make the mistake of thinking that incompletely dominant alleles are the same as co-dominant alleles. The following example is a visual simulation that will allow you to understand the differences in the relationships between incompletely dominant and co-dominant alleles. In anacondas skin color patterns are controlled by alleles at a single locus. A herpetologist performed a cross between parental snakes (shown within the circles on the figure) to determine if alleles controlling skin patterns were incompletely dominant or co-dominant. The herpetologist's expectations for either co-dominant or incompletely dominant genes are shown on the figure. Both co-dominant and incomplete dominant phenotypes can only result from a heterozygous genotype. However, there are differences in the phenotypes displayed by co-dominant and incompletely dominant alleles. In the heterozygous condition, incompletely dominant alleles display a phenotype that differs from the features and overall appearance either of the homozygous gene pairs. Both alleles in the heterozygous condition are expressed in a manner that produces a mixed phenotype such that neither the patterned nor the patternless phenotype is distinguishable in the progeny. The phenotype produced by heterozygous alleles in the co-dominant condition is also different from that produced by paired homozygous alleles. However, in co-dominance heterozygous alleles are expressed in a manner that the phenotypes conveyed by both alleles are clearly visible in the progeny. Parental Types Patterned Patternless Progeny Incomplete dominant Co-dominant 1. Assume alleles CP and CL controlling color patterns on anacondas are co-dominant. What are the genotypes of the parental animals shown on the figure? (2 pts) CP CP x CL CL 2. The herpetologist obtained a clutch of 8 eggs from a mating between F1 co-dominant progeny animals of the type shown on the figure. What is the likelihood that 3 of the eggs will produce animals with the parental phenotypes shown on the figure? All formulae and calculations must be shown to receive full points. (6 pts)
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One parent is homozygous for allele Cr (C. P. L. E.) and the other parent is homozygous for allele Cl (C. L. L. E.). ** Show more…
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Identify the statement that most accurately and completely describes codominance and incomplete dominance with respect to heterozygotes? A. Incomplete dominance - heterozygotes express a third phenotype that is in-between the homozygous phenotypes because the expression of one dominant allele looks different than the expression of two dominant alleles. Codominance - heterozygotes express the phenotype for both alleles. B. Incomplete dominance - heterozygotes express a third phenotype that is different from both homozygous phenotypes. Codominance - heterozygotes express the homozygous recessive phenotype because another gene at a different locus affects the expression of the dominant allele. C. Incomplete dominance - heterozygotes express a blended version of both dominant and recessive alleles and if crossed with another heterozygote their offspring can never express a homozygous phenotype. Codominance - heterozygotes weakly express the homozygous dominant phenotype because there is only one copy of the dominant allele. D. Incomplete dominance - heterozygotes express a little of each allele because both are present in the genotype. Codominance - heterozygotes express the dominant phenotype in some cells and the recessive phenotype in other cells. E. Incomplete dominance - heterozygotes express a third phenotype that affects multiple traits. Codominance - heterozygotes express neither the dominant or recessive allele but express a hybrid of both alleles instead.
Sri K.
Some heterozygotes express a phenotype that is intermediate between the dominant and recessive phenotype. For example, in 4 o'clock flowers, the gene for red pigmentation is dominant and the gene for white pigmentation is recessive. However, heterozygotes are pink. The dominant allele does not completely mask the expression of the recessive allele; it is incompletely dominant. 1. By observing flower color in 4 o'clock flowers, is it possible to unambiguously determine the genotype? YES/NO Is the same true for flower color in snow peas? YES/NO Why or why not? Another inheritance pattern of note is that of codominance. Here, both alleles for the same characteristic can be expressed. A common example of this is human ABO blood type. The alleles for the surface antigens are both dominant; the allele for no surface antigen is recessive. 2. If two individuals with blood type AB marry, what are the odds that each of their children will have the AB blood type? 3. A disputed paternity case! Hermione's new baby has a blood type of O. Her blood type is B and Ron Weasley's is A. Harry Potter, blood type AB, insists he is the child's father. CAN THIS BE TRUE???!
Dave K.
Many kinds of wild animals have the agouti coloring pattern, in which each hair has a yellow band around it. a. Black mice and other black animals do not have the yellow band; each of their hairs is all black. This absence of wild agouti pattern is called nonagouti. When mice of a true-breeding agouti line are crossed with nonagoutis, the $F_{1}$ is all agouti and the $F_{2}$ has a 3: 1 ratio of agoutis to nonagoutis. Diagram this cross, letting $A$ represent the allele responsible for the agouti phenotype and $a$ nonagouti. Show the phenotypes and genotypes of the parents, their gametes, the $F_{1}$, their gametes, and the $F_{2}$ b. Another inherited color deviation in mice substitutes brown for the black color in the wild-type hair. Such brown-agouti mice are called cinnamons. When wildtype mice are crossed with cinnamons, all of the $\mathrm{F}_{1}$ are wild type and the $\mathrm{F}_{2}$ has a 3: 1 ratio of wild type to cinnamon. Diagram this cross as in part $a$, letting $B$ stand for the wild-type black allele and $b$ stand for the cinnamon brown allele. c. When mice of a true-breeding cinnamon line are crossed with mice of a true-breeding nonagouti (black) line, all of the $F_{1}$ are wild type. Use a genetic diagram to explain this result. d. In the $F_{2}$ of the cross in part $c,$ a fourth color called chocolate appears in addition to the parental cinnamon and nonagouti and the wild type of the $\mathrm{F}_{1}$. Chocolate mice have a solid, rich brown color. What is the genetic constitution of the chocolates? e. Assuming that the $A / a$ and $B / b$ allelic pairs assort independently of each other, what do you expect to be the relative frequencies of the four color types in the $\mathrm{F}_{2}$ described in part $d ?$ Diagram the cross of parts $c$ and $d$ showing phenotypes and genotypes (including gametes). f. What phenotypes would be observed in what proportions in the progeny of a backcross of $\mathrm{F}_{1}$ mice from part $c$ with the cinnamon parental stock? With the nonagouti (black) parental stock? Diagram these backcrosses. g. Diagram a testcross for the $\mathrm{F}_{1}$ of part $c .$ What colors would result and in what proportions? h. Albino (pink-eyed white) mice are homozygous for the recessive member of an allelic pair $C / c,$ which assorts independently of the $A / a$ and $B / b$ pairs. Suppose that you have four different highly inbred (and therefore presumably homozygous) albino lines. You cross each of these lines with a true-breeding wild-type line, and you raise a large $\mathrm{F}_{2}$ progeny from each cross. What genotypes for the albino lines can you deduce from the following $\mathrm{F}_{2}$ phenotypes? $$\begin{array}{cccccc} & {4}{c} {\text {Phenotypes of progeny}} \\ { 2 - 5 } \mathrm{F}_{2} \text { of } \text { line } & \begin{array}{c} \text { Wild } \\ \text { type } \end{array} & \text { Black } & \begin{array}{c} \text { Cinna- } \\ \text { mon } \end{array} & \begin{array}{c} \text { Choco- } \\ \text { late } \end{array} & \text { Albino } \\ \hline 1 & 87 & 0 & 32 & 0 & 39 \\ 2 & 62 & 0 & 0 & 0 & 18 \\ 3 & 96 & 30 & 0 & 0 & 41 \\ 4 & 287 & 86 & 92 & 29 & 164 \\ \hline \end{array}$$ (Adapted from A. M. Srb, R. D. Owen, and R. S. Edgar General Genetics, 2nd ed. W. H. Freeman and Company, 1965.)
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