Solved Problems Module 2 Part 1

Solved Problems

Module 2

Part 1

1- A dominant allele H reduces the number of body bristles that Drosophila flies have, giving rise to a hairless phenotype. In the homozygous condition, H is lethal. An independently assorting dominant allele F has no effect on Bristle number except in the presence of H, in which case a single dose of F suppresses the hairless phenotype, thus restoring the hairy phenotype. However, F also is lethal in the homozygous (FF) condition.

What ratio of hairy to hairless flies would you find in the live progeny of a cross between two hairy flies both carrying H in the suppressed condition?
When the hairless progeny are backcrossed with a parental hairy fly, what phenotypic ratio would you expect to find among their live progeny?

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2- The frizzle fowl is much admired by poultry fanciers. It gets its name from the unusual way that its feathers curl up. Unfortunately, frizzle fowls do not breed true. When two fizzles are intercrossed, they always produce 50% frizzles, 25% normal and 25% with peculiar wooly feathers that soon fall out, leaving the birds naked.

Give a genetic explanation for these results, showing genotypes and phenotypes.
If you wanted to mass-produce frizzle fowls for sale, which types would be best to use as breeding pair?

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3- The flowers of nasturtiums may be single (S), double (D), or superdouble (Sd). Crosses between the varieties gave the progenies as listed in the following table, where pure means pure-breeding.

Cross	Parents	Progeny
1	pure S x pure D	All S
2	cross 1 F1 x cross 1 F1	78 S: 27 D
3	pure D x Sd	112 Sd: 108 D
4	pure S x Sd	8 Sd: 7 S
5	pure D x cross 4 Sd progeny	18 Sd: 19S
6	pure D x cross 4 S progeny	16S

Using your own genetic symbols, propose an explanation of these results, showing all the genotypes in each of the six rows.

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4- In Shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data were obtained from various crosses:

red x red -> all red

white x white -> all white

red x white -> all roan

roan x roan -> ¼ red, ½ roan, ¼ white

How is coat color inherited? What are the genotypes of parents and offspring for each cross?

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5- Erminette fowls have mostly white colored feathers with an occasional black one, giving them a flecked appearance. A cross of two erminettes produced 22 erminettes, 14 blacks, and 12 pure whites. What genetic basis of the erminette pattern is suggested? How would you test your hypothesis?

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6- Radishes may be long, round, or oval, and they may be red, white, or purple. You cross a long, white variety with a round, red variety and obtain an oval, purple F1.

The F2 shows nine phenotypic classes as follows:

9 long red; 15 long purple; 19 oval red; 32 oval purple; 8 long white; 16 round purple; 8 round white; 16 oval white; and 9 round red.

Provide a genetic explanation of these results. Be sure to define the genotypes and show the constitution of parents, F1 and F2.
Predict the genotypic and phenotypic proportions in the progeny of a cross between a long purple radish and oval purple one.

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7- In the multiple allele series that determines coat color in rabbits, C⁺ codes for agouti, C^ch for Chinchilla (a beige coat color), and C^h for Himalayan. Dominance is in the order C⁺ > C^ch > C^h. In a cross of C⁺/C^ch x C^ch/C^h, what proportion of progeny will be chinchilla?

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8- Black, Sepia, cream, and albino are all coat colors of guinea pigs. Individual animals (not necessarily from pure lines) showing these colors were intercrossed; the results are tabulated as follows, where the abbreviations A (albino), B (black), C (cream), and S (Sepia) represent the phenotypes:

Cross	Parental phenotypes	Progeny phenotypes
		B	S	C	A
1	B x B	22	0	0	7
2	B x A	10	9	0	0
3	C x C	0	0	34	11
4	S x C	0	24	11	12
5	B x A	13	0	12	0
6	B x C	19	20	0	0
7	B x S	18	20	0	0
8	B x S	14	8	6	0
9	S x S	0	26	9	0
10	C x A	0	0	15	17

Deduce the inheritance of these coat colors and use gene symbols of your own choosing. Show all the parent and progeny genotypes.
If the black animals in crosses 7 and 8 are crossed, what progeny proportions can you predict by using your model?

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9- On a fox ranch in Wisconsin, a mutation arose that gave a “platinum” coat color. The platinum color proved very popular with buyers of fox coats, but the breeders could not develop a pure breeding platinum strain. Every time two platinums were crossed, some normal foxes appeared in the progeny. For example, the repeated matings of the same pair of platinum produced 82 platinum and 38 normal progeny. All other such matings gave similar progeny ratios. State a concise genetic hypothesis that accounts for these results.

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10- A scientist investigated an inherited anomaly of the white blood cells of rabbits. This anomaly called Pelger anomaly, is the arrest of segmentation of the nuclei of certain white cells. This anomaly does not appear to seriously inconvenience the rabbits.

When rabbits showing the typical pelger anomaly were mated with rabbits from a true breeding normal stock, the progeny were 217 showing Pelger anomaly and 237 normal. What are the genotypes of the parents?
When rabbits with Pelger anomaly were mated to each other, the progeny were 223 normal, 439 showing the Pelger anomaly, and 39 extremely abnormal progeny. These very abnormal progeny not only had defective white blood cells, but also showed very severe skeletal deformities and almost all of them died soon after birth. In genetic terms, what do you suppose these extremely defective rabbits represented? What kind of inheritance are we dealing with here?

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