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Problem 1a
How was Mendel able to derive postulates concerning the behavior of 'unit factors' during gamete formation when he could not directly observe them?
Problem 1b
How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?
Problem 1c
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?
Problem 1d
Since experimental crosses are not performed in humans, how do we know how traits are inherited?
Problem 2
Write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.
Problem 3a
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.
Problem 3b
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.
Problem 3c
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.
Problem 3d
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).
Problem 4
Which of Mendel's postulates are illustrated by the pedigree that you constructed in Problem 3? List and define these postulates.
Problem 5
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?
Problem 6
What advantages were provided by Mendel's choice of the garden pea in his experiments?
Problem 7
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.
- Based on the preceding cross, what is the probability that an organism in the F₂ generation will have round seeds and green cotyledons and be true breeding?
Problem 8
Problem 9
Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.
Problem 10a
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.
Problem 10b
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?
Problem 10c
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
Problem 11
What is the basis for homology among chromosomes?
Problem 12a
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
Problem 12b
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.
Problem 12c
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.
Problem 13
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?
Problem 14
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.