6: Chromosomal Inheritance
Students trace inheritance of X-linked genes through meiosis, predict progeny outcomes from sex-linked crosses, and explain the chromosomal basis of inheritance.
LibreTexts reference: Chapter 6: Chromosomal Inheritance 
Matching Meiosis Prophase I Stages to Descriptions
Click to show Matching Meiosis Prophase I Stages to Descriptions example problem
Match each of the following stages of meiosis prophase I with their corresponding partial descriptions.
Note: Each choice will be used exactly once.
| Your Choice | Prompt | |
|---|---|---|
| 1. Diplotene or Diakinesis, combined | ||
| 2. Leptotene | ||
| 3. Pachytene, early or late | ||
| 4. Zygotene |
Drag one of the choices below:
- A. the paired chromosomes begin to separate
- B. thread-like chromomeres become visible along the chromosomes
- C. crossing over occurs between homologous chromosomes
- D. the synapsis process forms numerous points of contact between homologs
Matching Meiosis Terms to Definitions
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Match each of the following Meiosis terms with their corresponding definitions.
Note: Each choice will be used exactly once.
| Your Choice | Prompt | |
|---|---|---|
| 1. sister chromatids | ||
| 2. homologous chromosomes | ||
| 3. crossing over | ||
| 4. synapsis |
Drag one of the choices below:
- A. the joining of the two homologous chromosomes
- B. two chromosomes containing identical genetic loci although possibly different allelic forms
- C. a process by which parts of homologous chromosomes are interchanged
- D. two identical copies of the same chromosome attached to each other by the centromere
Matching Sex Determination Systems to Descriptions
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Match each of the following sex determination systems with their corresponding descriptions.
Note: Each choice will be used exactly once.
| Your Choice | Prompt | |
|---|---|---|
| 1. Z-W system | ||
| 2. X-O system | ||
| 3. X-Y system | ||
| 4. Haplo-Diploid system |
Drag one of the choices below:
- A. females ♀ are homogametic and males ♂ are heterogametic
- B. unfertilized eggs develop into males ♂
- C. females ♀ are heterogametic and males ♂ are homogametic
- D. females ♀ have two homologous sex chromosomes, males ♂ have only one
True/False Statements About Mitosis and Meiosis
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Which one of the following statements is TRUE concerning mitosis and meiosis cell division?
Meiosis Prophase I Stages from Descriptions
Click to show Meiosis Prophase I Stages from Descriptions example problem
Which one of the following stages of meiosis prophase I correspond to the partial description 'strands of homologous chromosomes line up and become pairs'.
Meiosis Terms from Definitions
Click to show Meiosis Terms from Definitions example problem
Which one of the following Meiosis terms correspond to the definition 'the actual exchange of segments between homologous chromosomes'.
Sex Determination Systems from Descriptions
Click to show Sex Determination Systems from Descriptions example problem
Which one of the following sex determination systems correspond to the description 'females ♀ are homogametic and males ♂ are heterogametic'.
Fraction of Daughters with Both AIS and HD
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Androgen insensitivity syndrome (AIS) is an X-linked recessive genetic disorder that is caused by a mutation in the AR gene for the human androgen receptor. This results in partial or complete inability of cells to respond to androgens. The disorder affects 1 in 20,000. Individuals affected with AIS have impaired development of male genitals and male secondary sexual characteristics at puberty. The defective gene for AIS is located on the long arm of chromosome X at position 11.
Marfan syndrome (MFS) is an autosomal dominant genetic disorder that is caused by a mutation in FBN1 gene that makes fibrillin protein. This results in weaked connective tissue throughout the body. The disorder affects 1 in 10,000 people. Individuals affected with MFS have tall and thin features with serious complications involving the heart and aorta. The defective gene for MFS is located on the long arm of chromosome 15 at position 21.1.
A man (♂) with both AIS and MFS genetic disorders marries a wild-type phenotype woman (♀) with neither disorder. The father (♂) of the woman has the AIS genetic disorder,but mother (♀) of the woman does not. The father (♂) of the man is wild-type phenotype and does not have the MFS genetic disorder.
Reminder: AIS is X-linked recessive and MFS is autosomal dominant.
What fraction of their sons (♂) will have both AIS and MFS genetic disorders?
Combined Dominant and X-Linked Recessive Inheritance Variations
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Androgen insensitivity syndrome (AIS) is an X-linked recessive genetic disorder that is caused by a mutation in the AR gene for the human androgen receptor. This results in partial or complete inability of cells to respond to androgens. The disorder affects 1 in 20,000. Individuals affected with AIS have impaired development of male genitals and male secondary sexual characteristics at puberty. The defective gene for AIS is located on the long arm of chromosome X at position 11.
Huntington's disease (HD) is an autosomal dominant genetic disorder that is caused by an increase in trinucleotide repeats in the HTT gene. This results in a mutated Huntington protein that is toxic to certain cell types, particularly brain cells. The disorder affects 1 in 10,000 adults of European descent. Individuals affected with HD have physical abilities that gradually worsen and mental abilities that decline into dementia. The defective gene for HD is located on the short arm of chromosome 4 at position 16.3.
A man (♂) and a woman (♀) are planning a family. The man (♂) has AIS. The woman (♀) is a carrier for AIS; her father has AIS, but her mother does not. The man (♂) does not have HD. The woman (♀) has HD. The father (♂) of the woman (♀) does not have HD.
Reminder: AIS is X-linked recessive and HD is autosomal dominant.
What fraction of their daughters (♀) will have HD but not AIS?
Parent Genotypes in X-Linked Recessive Crosses
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The white-eyed (mutant) phenotype is an X-linked recessive disorder in fruit flies. The red-eyed (wildtype) allele, +, is dominant to the white (mutant) allele, w. The offspring of size 320 from the mating of a single female (♀) and a single male (♂) are shown in the table below:
| phenotype | female (♀) | male (♂) |
|---|---|---|
| red-eyed (wildtype) | 149 | 84 |
| white-eyed (mutant) | 0 | 87 |
What are the genotypes of the parents in this cross?
X-linked Eye Color Inheritance
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In fruit flies, eye color is X-linked with red eyes dominant to white eyes. A true-breeding white-eyed female is crossed with a true-breeding red-eyed male.
Which statement best describes the F1 offspring?
X-linked Coat Color Probability
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In cats, coat color is X-linked. The orange (O) and black (B) alleles are codominant, so heterozygous females are tortoiseshell.
A tortoiseshell female (♀) mates with a orange male (♂).
What fraction of daughters (♀) are expected to be tortoiseshell?