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

Punnett Square Probability

General Biology

13. Mendelian Genetics

Punnett Square Probability

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1:15 minutes

Problem 13

Textbook Question

In fruit flies, the genes for wing shape and body stripes are linked. In a fly whose genotype is WwSs, W is linked to S, and w is linked to s. Show how this fly can produce gametes containing four different combinations of alleles.
Which are parental-type gametes?
Which are recombinant gametes? How are the recombinants produced?

Verified step by step guidance

Understand the concept of linked genes: Linked genes are located close together on the same chromosome and tend to be inherited together. In this case, W (wing shape) is linked to S (body stripes), and w is linked to s.

Determine the possible gametes: Since the fly has the genotype WwSs, it can produce gametes with combinations of alleles. Parental-type gametes are those that retain the original linkage (WS and ws), while recombinant gametes are those that result from crossing over (Ws and wS).

Explain how crossing over occurs: During meiosis, homologous chromosomes can exchange genetic material in a process called crossing over. This exchange can break the linkage between W and S or w and s, creating recombinant gametes (Ws and wS).

List the four possible gametes: The fly can produce gametes with the following combinations of alleles: WS (parental type), ws (parental type), Ws (recombinant type), and wS (recombinant type).

Clarify the distinction between parental and recombinant gametes: Parental-type gametes (WS and ws) maintain the original linkage of alleles, while recombinant gametes (Ws and wS) result from crossing over during meiosis, which reshuffles the alleles.

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Key Concepts

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

Linked Genes

Linked genes are genes that are located close to each other on the same chromosome and tend to be inherited together during meiosis. This linkage affects the assortment of alleles into gametes, as they do not assort independently like unlinked genes. In the case of the fruit fly, the genes for wing shape (W/w) and body stripes (S/s) are linked, influencing the combinations of alleles in the gametes produced.

Gamete Formation and Allele Combinations

During gamete formation, specifically meiosis, alleles segregate into different gametes. For the genotype WwSs, the possible combinations of alleles in the gametes can be determined by considering the parental alleles and their linkage. The four gametes produced from this genotype are WS, Ws, wS, and ws, representing different combinations of the alleles for wing shape and body stripes.

Parental and Recombinant Gametes

Parental-type gametes are those that contain the same allele combinations as the parents, while recombinant gametes have new combinations of alleles due to crossing over during meiosis. In this scenario, WS and ws are parental-type gametes, while Ws and wS are recombinant gametes. Recombinants are produced when homologous chromosomes exchange segments during prophase I of meiosis, leading to new allele combinations.

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Related Practice

Textbook Question

The genotype of F₁individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F₂ offspring will have the following genotypes?

a. aabbccdd

b. AaBbCcDd

c. AABBCCDD

d. AaBBccDd

e. AaBBCCdd

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Textbook Question

Both Tim and Jan have a widow's peak (see Module 9.8), but Mike has a straight hairline.

What are their genotypes?

What is the probability that Tim and Jan's next child will have freckles and a straight hairline?

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Textbook Question

What is the probability that each of the following pairs of parents will produce the indicated offspring? (Assume independent assortment of all gene pairs.)

a. AABBCC×aabbcc→AaBbCc

b. AABbCc×AaBbCc→AAbbCC

c. AaBbCc×AaBbCc→AaBbCc

d. aaBbCC×AABbcc→AaBbCc

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Textbook Question

In rabbits, black hair depends on a dominant allele, B, and brown hair on a recessive allele, b. Short hair is due to a dominant allele, S, and long hair to a recessive allele, s. If a true-breeding black short-haired male is mated with a brown long-haired female, describe their offspring. What will be the genotypes of the offspring? If two of these F1 rabbits are mated, what phenotypes would you expect among their offspring? In what proportions?

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Textbook Question

The breakthrough that led Bateson and Punnett to recognize the existence of linked genes was the appearance of unexpected results after they crossed double heterozygous pea plants (PpLl) with each other. Imagine that you have a group of Labrador retrievers that are all heterozygous for both coat color and blindness (BbNn). If you used this group of dogs to produce 160 puppies, how many puppies of each phenotype do you expect to get if the genes are not linked? How would the results differ if the genes are in fact linked?

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Multiple Choice

In a Punnett square where both parents are heterozygous for attached earlobes (Ee), what is the probability that their offspring will have unattached earlobes?

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Multiple Choice

Why can the principles of probability be used to predict the outcomes of genetic crosses?

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Multiple Choice

In a Punnett square where both parents are heterozygous for unattached earlobes (Ee), what is the probability that the offspring in square 2 will have unattached earlobes?