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Chapter 6: Problem 19

Most of the feathers of erminette fowl are light colored, with an occasional black one, giving a flecked appearance. A cross of two erminettes produced a total of 48 progeny, consisting of 22 erminettes, 14 blacks, and 12 pure whites. What genetic basis of the erminette pattern is suggested? How would you test your hypotheses?

Short Answer

Expert verified
The erminette pattern suggests a BW heterozygous genotype. Cross two erminettes (BW) to expect a 1:2:1 ratio of black, erminette, and white chicks. Confirm with a chi-squared test.

Step by step solution

01

Understanding the Genetic Pattern

The progeny distribution among erminette, black, and white suggests a pattern that can be the result of a genetic cross. To hypothesize, consider that erminette could be heterozygous with one allele for black and one for white.
02

Assuming a Genotype

Assume 'B' represents the allele for black feathers and 'W' for white feathers. Then the erminette (BW) results from a heterozygous combination of these alleles. Black would be homozygous dominant (BB) and white homozygous recessive (WW).
03

Setting Up the Punnett Square

Cross two heterozygous erminette (BW) to predict the offspring ratios. The Punnett Square will include combinations: BB, BW, WB, WW.
04

Predicting Offspring Ratios

From the Punnett Square, expect 1:2:1 ratio: 1 BB (black), 2 BW (erminette), and 1 WW (white). This means 25% black, 50% erminette, and 25% white.
05

Comparing Predicted and Observed Ratios

The cross produced 48 offspring: 14 black (BB), 22 erminette (BW), and 12 white (WW). Compare with predicted ratio to see if it fits: 14/48 鈮� 25% black, 22/48 鈮� 50% erminette, and 12/48 鈮� 25% white, which fits the predicted genetic pattern.
06

Testing the Hypothesis

To test the hypothesis, repeat the same cross with a larger number of erminette. Use the chi-squared test to compare the observed offspring ratios with the expected 1:2:1 ratio to confirm the hypothesis.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Punnett Square
A Punnett Square is a helpful diagram used in genetics to predict the outcome of a particular cross or breeding experiment. It was named after Reginald C. Punnett, an English geneticist. By setting up a Punnett Square, you can easily visualize the possible genotypes of the offspring based on the genetic makeup of the parents.
For example, consider the erminette chickens exercise. When two heterozygous erminette chickens (genotype BW) are crossed, a Punnett Square helps determine the possible combinations of the alleles B (black) and W (white).
  • The top row typically represents one parent's alleles.
  • The side column represents the other parent's alleles.
  • By filling in the squares, you can see all potential allele combinations in the offspring.
This visual tool helps simplify how we predict the proportions of genotypes鈥攁nd often the resulting phenotypes鈥攐f the offspring, making it an essential tool for studying Mendelian inheritance.
Genotype
A genotype is the genetic makeup of an organism in terms of the alleles present for a specific trait. It's essentially the "code" of an organism's DNA that determines a particular characteristic or set of characteristics.
In the context of the erminette pattern, the genotype is crucial in understanding why some chickens are black, some are white, and some have the unique erminette appearance. Here, the alleles are:
  • 'B' for black feathers.
  • 'W' for white feathers.
The genotype combinations can be:
  • 'BB' for black chickens.
  • 'WW' for white chickens.
  • 'BW' for erminette chickens.
Thus, identifying genotypes helps you make predictions about phenotype鈥攖he observable characteristics鈥攁nd also serves as a way to test genetic hypotheses.
Heterozygous
The term heterozygous describes an organism that has two different alleles for a particular gene. In simplest terms, it means possessing both a dominant allele and a recessive allele for a specific trait, such as having one 'B' (black) and one 'W' (white) in erminette chickens.
In this exercise with erminette chickens, individuals with the heterozygous genotype (BW) display the flecked feather pattern. This occurs because neither allele is completely dominant over the other, resulting in a mixed phenotype.
  • Heterozygous genotypes often result in an intermediate phenotype when traits demonstrate incomplete dominance.
  • The appearance of intermediate traits makes heterozygous organisms like erminette chickens particularly interesting in genetic studies.
By examining heterozygous offspring, scientists can uncover more about how specific genetic traits are inherited, making it a key concept in understanding genetic variability and predicting inheritance patterns.

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Most popular questions from this chapter

In a maternity ward, four babies become accidentally mixed up. The ABO types of the four babies are known to be \(\mathrm{O}, \mathrm{A}, \mathrm{B},\) and \(\mathrm{AB}\). The \(\mathrm{ABO}\) types of the four sets of parents are determined. Indicate which baby belongs to each set of parents: (a) \(A B \times O,(b) A \times O,(c) A x\) \(\mathrm{AB},(\mathrm{d}) \mathrm{O} \times \mathrm{O}\).

In sweet peas, the synthesis of purple anthocyanin pigment in the petals is controlled by two genes, \(B\) and \(D\) The pathway is a. What color petals would you expect in a purebreeding plant unable to catalyze the first reaction? b. What color petals would you expect in a purebreeding plant unable to catalyze the second reaction? c. If the plants in parts \(a\) and \(b\) are crossed, what color petals will the \(F_{1}\) plants have? d. What ratio of purple:blue:white plants would you expect in the \(\mathrm{F}_{2}\) ?

For a period of several years, Hans Nachtsheim investigated an inherited anomaly of the white blood cells of rabbits. This anomaly, termed the Pelger anomaly, is the arrest of the segmentation of the nuclei of certain white cells. This anomaly does not appear to seriously inconvenience the rabbits. a. When rabbits showing the typical Pelger anomaly were mated with rabbits from a true-breeding normal stock, Nachtsheim counted 217 offspring showing the Pelger anomaly and 237 normal progeny. What appears to be the genetic basis of the Pelger anomaly? b. When rabbits with the Pelger anomaly were mated with each other, Nachtsheim found 223 normal progeny, 439 showing the Pelger anomaly, and 39 extremely abnormal progeny. These very abnormal progeny not only had defective white blood cells, but also showed severe deformities of the skeletal system; almost all of them died soon after birth. In genetic terms, what do you suppose these extremely defective rabbits represented? Why do you suppose there were only 39 of them? c. What additional experimental evidence might you collect to support or disprove your answers to part \(b\) ? d. In Berlin, about 1 human in 1000 shows a Pelger anomaly of white blood cells very similar to that described for rabbits. The anomaly is inherited as a simple dominant, but the homozygous type has not been observed in humans. Can you suggest why, if you are permitted an analogy with the condition in rabbits? e. Again by analogy with rabbits, what phenotypes and genotypes might be expected among the children of a man and woman who both show the Pelger anomaly? (Problem 26 is from A. M. Srb, R. D. Owen, and R. S. Edgar, General Genetics, 2nd ed. W. H. Freeman and Company, \(1965 .\))

In corn, three dominant alleles, called \(A, C,\) and \(R\) must be present to produce colored seeds. Genotype \(A /-; C /-; R /-\) is colored; all others are colorless. A colored plant is crossed with three tester plants of known genotype. With tester \(a / a ; c / c ; R / R,\) the colored plant produces 50 percent colored seeds; with \(a / a ; C / C ; r / r,\) it produces 25 percent colored; and with \(A / A ; c / c ; r / r,\) it produces 50 percent colored. What is the genotype of the colored plant?

You have been given a virgin Drosophila female. You notice that the bristles on her thorax are much shorter than normal. You mate her with a normal male (with long bristles) and obtain the following \(\mathrm{F}_{1}\) progeny: \(\frac{1}{3}\) short-bristled females, \(\frac{1}{3}\) long-bristled females, and \(\frac{1}{3}\) long-bristled males. A cross of the \(\mathrm{F}_{1}\) long- bristled females with their brothers gives only long-bristled \(\mathrm{F}_{2}\). A cross of short-bristled females with their brothers gives \(\frac{1}{3}\) short-bristled females, \(\frac{1}{3}\) long-bristled females, and \(\frac{1}{3}\) long-bristled males. Provide a genetic hypothesis to account for all these results, showing genotypes in every cross.
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