How was Mendel able to derive postulates concerning the behavior of 'unit factors' during gamete formation when he could not directly observe them?

How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?

The discussion focuses on the Mendelian postulates, probability, and pedigree analysis. We also considered some of the methods and reasoning by which these ideas, concepts, and techniques were developed. On the basis of these discussions, what answers would you propose to the following questions:

In analyzing genetic data, how do we know whether deviation from the expected ratio is due to chance rather than to another, independent factor?

Since experimental crosses are not performed in humans, how do we know how traits are inherited?

Write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

Two normal parents have five children: four normal and one albino.

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

A normal male and an albino female have six children, all normal.

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

A normal male and an albino female have six children, three normal and three albino.

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).

Which of Mendel's postulates are illustrated by the pedigree that you constructed in Problem 3? List and define these postulates.

Discuss how Mendel's monohybrid results served as the basis for all but one of his postulates. Which postulate was not based on these results? Why?

What advantages were provided by Mendel's choice of the garden pea in his experiments?

Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F₁ plants had round seeds with yellow cotyledons. Diagram this cross through the F₂ generation, using both the Punnett square and forked-line, or branch diagram, methods.

Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Diagram this cross, showing the genotypes and phenotypes.

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. What will the offspring be like if two F₂ white guinea pigs are mated?

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Two different matings were made between black members of the F₂ generation, with the following results. Diagram each of the crosses.

Cross Offspring

Cross 1 All black

Cross 2 3/4 black, 1/4 white

What is the basis for homology among chromosomes?

In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation. gray, long x ebony, vestigial

In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation. gray, vestigial, x-shaped, and long.

In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation. gray, long x gray, and vestigial.

How many different types of gametes can be formed by individuals of the following genotypes:

(a) AaBb

(b) AaBB

(c) AaBbCc

(d) AaBBcc

(e) AaBbcc

(f) AaBbCcDdEe

What are the gametes in each case?

Mendel crossed peas having green seeds with peas having yellow seeds. The F₁ generation produced only yellow seeds. In the F₂, the progeny consisted of 6022 plants with yellow seeds and 2001 plants with green seeds. Of the F₂ yellow-seeded plants, 519 were self-fertilized with the following results: 166 bred true for yellow and 353 produced an F₃ ratio of 3/4 yellow: 1/4 green. Explain these results by diagramming the crosses.

In a study of black guinea pigs and white guinea pigs, 100 black animals were crossed with 100 white animals, and each cross was carried to an F₂ generation. In 94 of the crosses, all the F₁ offspring were black and an F₂ ratio of 3 black:1 white was obtained. In the other 6 cases, half of the F₁ animals were black and the other half were white. Why? Predict the results of crossing the black and white F₁ guinea pigs from the 6 exceptional cases.

Mendel crossed peas having round green seeds with peas having wrinkled yellow seeds. All F₁ plants had seeds that were round and yellow. Predict the results of testcrossing these F₁ plants.

Thalassemia is an inherited anemic disorder in humans. Affected individuals exhibit either a minor anemia or a major anemia. Assuming that only a single gene pair and two alleles are involved in the inheritance of these conditions, is thalassemia a dominant or recessive disorder?

The following are F₂ results of two of Mendel's monohybrid crosses.

For each cross, state a null hypothesis to be tested using x² analysis. Calculate the x² value and determine the p value for both. Interpret the p-values. Can the deviation in each case be attributed to chance or not? Which of the two crosses shows a greater amount of deviation?

In assessing data that fell into two phenotypic classes, a geneticist observed values of 250:150. She decided to perform a $\chi$² analysis by using the following two different null hypotheses:

(a) the data fit a 3:1 ratio, and

(b) the data fit a 1:1 ratio.

Calculate the $\chi$ ² values for each hypothesis. What can be concluded about each hypothesis?

The basis for rejecting any null hypothesis is arbitrary. The researcher can set more or less stringent standards by deciding to raise or lower the p value used to reject or not reject the hypothesis. In the case of the chi-square analysis of genetic crosses, would the use of a standard of p = 0.10 be more or less stringent about not rejecting the null hypothesis? Explain.