Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

29. Heredity

Patterns of Inheritance

Anatomy & Physiology

29. Heredity

Patterns of Inheritance

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Problem 4

Textbook Question

Recessive X-linked traits
(a) Are passed from fathers to their sons
(b) Are more likely to be expressed in males
(c) Always affect some aspect of the reproductive system
(d) Are never expressed in females
(e) Cannot be passed from mothers to daughters

Verified step by step guidance

Understand the concept of X-linked inheritance: X-linked traits are associated with genes located on the X chromosome. Males (XY) have one X chromosome, while females (XX) have two. Recessive X-linked traits are expressed in males if the single X chromosome carries the recessive allele, while females must have the recessive allele on both X chromosomes to express the trait.

Analyze option (a): Recessive X-linked traits are not passed from fathers to their sons because fathers contribute the Y chromosome to their sons, not the X chromosome. Sons inherit their X chromosome from their mothers.

Analyze option (b): Recessive X-linked traits are more likely to be expressed in males because males have only one X chromosome. If that X chromosome carries the recessive allele, the trait will be expressed since there is no second X chromosome to mask it.

Analyze option (c): Recessive X-linked traits do not always affect the reproductive system. They can affect various systems, such as vision (e.g., red-green color blindness) or blood clotting (e.g., hemophilia).

Analyze option (d) and (e): Recessive X-linked traits can be expressed in females if both X chromosomes carry the recessive allele, though this is less common. Additionally, these traits can be passed from mothers to daughters if the mother carries the recessive allele on one or both of her X chromosomes.

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Key Concepts

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

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. Since males have one X and one Y chromosome, they are more likely to express recessive traits linked to the X chromosome. In contrast, females have two X chromosomes, which can mask the expression of recessive traits if a dominant allele is present.

Recessive Traits

Recessive traits are characteristics that are expressed only when an individual has two copies of the recessive allele. In the case of X-linked traits, males, having only one X chromosome, will express the trait if their single X carries the recessive allele. Females, however, need two copies of the recessive allele (one on each X chromosome) to express the trait.

Sex-linked Traits

Sex-linked traits are those associated with genes found on the sex chromosomes, primarily the X chromosome. These traits often show different patterns of inheritance in males and females due to the differing number of X chromosomes. Understanding sex-linked traits is crucial for predicting inheritance patterns and the likelihood of expression in offspring.

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Related Practice

Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(a) Children who exhibit the trait have at least one parent who also exhibits it.

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Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(b) Children exhibit the trait even though neither parent does.

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Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(d) The trait is expressed equally in daughters and sons.

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Textbook Question

Distinguish between the following paired terms:

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Textbook Question

Indicate the type of inheritance involved in each of the following situations.

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Textbook Question

Hemophilia A, a condition in which blood does not clot properly, is a recessive trait located on the X chromosome (Xʰ). Suppose that a woman who is heterozygous for this trait (XXʰ) has children with a normal male (XY). What is the probability that the couple will have daughters with hemophilia? What is the probability that the couple will have sons with hemophilia?

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Textbook Question

Distinguish between the following paired terms:

(b) heterozygous and homozygous,

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Multiple Choice

An allele that is able to mask the expression of its partner allele is said to be __________.

870

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