Chapter 4: Problem 29
What genetic criteria distinguish a case of extranuclear inheritance from (a) a case of Mendelian autosomal inheritance; (b) a case of \(\mathrm{X}\) -linked inheritance?
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Chapter 4: Problem 29
What genetic criteria distinguish a case of extranuclear inheritance from (a) a case of Mendelian autosomal inheritance; (b) a case of \(\mathrm{X}\) -linked inheritance?
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In goats, development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the \(\mathrm{F}_{2}\) generation: \(P_{1}:\) bearded female \(\times\) beardless male \(\mathrm{F}_{1}:\) all bearded males and beardless females \\[ \mathrm{P}_{1} \times \mathrm{F}_{1} \longrightarrow\left\\{\begin{array}{l} 1 / 8 \text { beardless males } \\ 3 / 8 \text { bearded males } \\ 3 / 8 \text { beardless females } \\ 1 / 8 \text { bearded females }\end{array}\right.\\] Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.
In foxes, two alleles of a single gene, \(P\) and \(p,\) may result in lethality \((P P),\) platinum coat \((P p),\) or silver coat \((p p) .\) What ratio is obtained when platinum foxes are interbred? Is the \(P\) allele behaving dominantly or recessively in causing (a) lethality; platinum coat color?
Labrador retrievers may be black, brown, or golden in color (see the chapter opening photograph on \(\mathrm{p} .53\) ). Although each color may breed true, many different outcomes occur if numerous litters are examined from a variety of matings, where the parents are not necessarily true-breeding. The following results show some of the possibilities. Propose a mode of inheritance that is consistent with these data, and indicate the corresponding genotypes of the parents in each mating. Indicate as well the genotypes of dogs that breed true for each color. (a) black \(\times\) brown \(\longrightarrow\) all black (b) black \(\times\) brown \(\longrightarrow \quad 1 / 2\) black \(1 / 2\) brown (c) black \(\times\) brown \(\longrightarrow \quad 3 / 4\) black \(1 / 4\) golden (d) black \(\quad \times\) golden \(\longrightarrow \quad\) all black (e) black \(\times\) golden \(\longrightarrow \quad 4 / 8\) golden 318 black \(1 / 8\) brown (f) black \(\times\) golden \(\longrightarrow \quad 2 / 4\) golden \(1 / 4\) black \(1 / 4\) brown (8) brown \(\times\) brown \(\longrightarrow \quad 3 / 4\) brown \(1 / 4\) golden (h) black \(\times\) black \(\longrightarrow 9 / 16\) black \(4 / 16\) golden \(3 / 16\) brown
Horses can be cremello (a light cream color), chestnut (a reddish brown color), or palomino (a golden color with white in the horse's tail and mane).Of these phenotypes, only palominos never breed true. The following results have been observed: (a) From these results, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes. (b) Predict the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of many initial matings between cremello and chestnut horses.
In Drosophila, an \(\mathrm{X}\) -linked recessive mutation, scalloped (sd), causes irregular wing margins. Diagram the \(F_{1}\) and \(F_{2}\) results if (a) a scalloped female is crossed with a normal male; (b) a scalloped male is crossed with a normal female. Compare these results to those that would be obtained if the scalloped gene were autosomal.
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