Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

13. Mendelian Genetics

Test Crosses

General Biology

13. Mendelian Genetics

Test Crosses

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4:45 minutes

Problem 10a

Textbook Question

The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a 'crested' appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of non-crested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested. For these three crosses, provide genotypes for parents and offspring that are consistent with these results.

Verified step by step guidance

Step 1: Determine the inheritance pattern. The data suggests that the crested trait is dominant because when two crested birds are crossed, all offspring are crested. This indicates that the crested phenotype (C) is dominant over the non-crested phenotype (c).

Step 2: Analyze the first cross (22 non-crested, 7 crested). Since both parents are non-crested and produce both crested and non-crested offspring, they must be heterozygous (Cc) to allow for the appearance of the dominant crested trait in their offspring.

Step 3: Assign genotypes to the offspring from the first cross. The ratio of non-crested to crested (approximately 3:1) suggests a Mendelian inheritance of a single gene. Therefore, the genotypes of the offspring are likely 1 CC (crested), 2 Cc (crested), and 1 cc (non-crested).

Step 4: Examine the second cross (two crested birds producing all crested offspring). Both parents are likely CC, as crossing two CC would result in 100% crested offspring (CC).

Step 5: Evaluate the third cross (7 non-crested, 6 crested from a non-crested and a crested parent). The non-crested parent must be cc, and the crested parent must be Cc, as this cross produces about a 1:1 ratio of non-crested to crested, consistent with a cross of cc x Cc.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Genetics and Inheritance Patterns

Genetics is the study of heredity and the variation of inherited characteristics. In this context, understanding inheritance patterns, such as dominant and recessive traits, is crucial. The crested appearance in pigeons likely follows Mendelian inheritance, where one allele may dominate over another, influencing the phenotype of the offspring.

Phenotype and Genotype

The phenotype refers to the observable traits of an organism, such as feather appearance in pigeons, while the genotype is the genetic makeup that determines these traits. In this scenario, the non-crested and crested phenotypes suggest different genotypes, which can be represented using symbols to denote dominant and recessive alleles.

Punnett Squares and Genetic Crosses

Punnett squares are a tool used to predict the genotypes of offspring from genetic crosses. By analyzing the crosses described, one can set up Punnett squares to visualize the potential combinations of alleles from the parents, helping to determine the expected ratios of phenotypes in the offspring based on the genotypes of the parents.

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Related Practice

Multiple Choice

To identify the genotype of a yellow-seeded pea plant as either homozygous dominant (YY) or heterozygous

(Yy), you could do a test cross between your mystery plant and a plant with a genotype of _______.

Two black female mice are crossed with a brown male. In several litters, female I produced 9 black offspring and 7 brown; female II produced 57 black offspring. What deductions can you make about the inheritance of black and brown coat color in mice? What are the genotypes of the parents?

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Textbook Question

In flies, small wings are recessive to normal wings. If a cross between two flies produces 8 small-wing offspring and 28 normal-wing offspring, what are the most likely genotypes of the parents? (Use S to represent the normal-wing allele and s to represent the short-wing allele.)

In 1981, a stray black cat with unusual rounded, curled-back ears was adopted by a family in California. Hundreds of descendants of the cat have since been born, and cat fanciers hope to develop the curl cat into a show breed. Suppose you owned the first curl cat and wanted to develop a true-breeding variety. How would you determine whether the curl allele is dominant or recessive? How would you obtain true-breeding curl cats? How could you be sure they are true-breeding?

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Textbook Question

In 1981, a stray black cat with unusual rounded, curled-back ears was adopted by a family in Lakewood, California. Suppose you owned the first curl cat and wanted to breed it to develop a true-breeding variety. Describe tests that would determine whether the curl gene is dominant or recessive and whether it is autosomal or sex-linked. Explain why you think your tests would be conclusive. Describe a test to determine that a cat is true-breeding.

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Textbook Question

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows: What is the genotype of the male parent?

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