6: Chromosomal Inheritance

Chromosome behavior in meiosis, sex-linkage, and the chromosomal basis of inheritance.

LibreTexts reference: Chromosomal Inheritance

Stages and Descriptions of Meiosis Prophase I

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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
	Drop Your Choice Here	1. Diplotene and/or Diakinesis
	Drop Your Choice Here	2. Early/Late Pachytene
	Drop Your Choice Here	3. Leptotene
	Drop Your Choice Here	4. Zygotene

Drag one of the choices below:

• A. the swapping of genetic material occurs at the chiasmata
• B. homologous chromosomes come together and pair
• C. chromosomes first appear as fine discrete threads
• D. chromosomes are at their most condensed form

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Matching Meiosis Terms with 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
	Drop Your Choice Here	1. synapsis
	Drop Your Choice Here	2. crossing over
	Drop Your Choice Here	3. sister chromatids
	Drop Your Choice Here	4. homologous

Drag one of the choices below:

• A. corresponding or alike in certain critical attributes
• B. two homologous chromosomes line up and parts of the chromosomes can be exchanged
• C. the lengthwise pairing of homologous chromosomes
• D. two identical copies of the same chromosome attached to each other by the centromere

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Sex Determination Systems and Their 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
	Drop Your Choice Here	1. X-Y system
	Drop Your Choice Here	2. Haplo-Diploid system
	Drop Your Choice Here	3. Z-W system
	Drop Your Choice Here	4. X-O system

Drag one of the choices below:

• A. males ♂ develop from unfertilized eggs and thus have no fathers
• B. sex of the offspring depends on whether or NOT a sex chromosome is present in the male ♂ gamete
• C. found in most birds, many reptiles, and some insects
• D. females ♀ have two of the same kind of sex chromosome

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Stages of Meiosis Prophase I

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Which one of the following stages of meiosis prophase I correspond to the partial description 'homologous chromosomes are held together only by the chiasmata'.

• Diplotene and/or Diakinesis
• Early/Late Pachytene
• Leptotene
• Zygotene

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Identification of Meiosis Terms Based on Definitions

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Which one of the following Meiosis terms correspond to the definition 'the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring'.

• chiasmata
• crossing over
• homologous
• homologous chromosomes

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Sex Determination Systems Identification

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Which one of the following sex determination systems correspond to the description ' male ♂ sperm normally contain either one sex chromosome or no sex chromosomes at all'.

• Haplo-Diploid system
• X-O system
• X-Y system
• Z-W system

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True/False Statements on Mitosis and Meiosis

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Which one of the following statements is FALSE regarding mitosis and meiosis cell division?

• Meiosis occurs in the gamete cells and facilitates sexual reproduction in living organisms
• Meiosis daughter cells contain half of the genetic material which is a mix of both the maternal and paternal genes
• Each daughter cell formed by mitosis has the same kinds of chromosomes as the parent cell
• Mitosis I is the only stage where homologous chromosomes pair up and exchange genetic material
• Meiosis occurs in two phases, that is, meiosis I and meiosis II

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Genetic Inheritance Patterns in X-Linked Recessive and Autosomal Dominant Disorders

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Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder that is caused by mutations in the DMD gene. This results in dystrophin is responsible for connecting the actin cytoskeleton to the extracellular matrix (ECM) in muscle cells. The disorder affects 1 in 20,000 males. Individuals affected with DMD have muscle weakness, trouble standing up, which eventually leads to loss of skeletal muscle control, respiratory failure, and death. The defective gene for DMD is located on the short arm of chromosome X at position 21.2.
Achondroplasia is an autosomal dominant genetic disorder that is caused by a mutation in the FGFR3 gene. This results in a mutated protein that interacts negatively with growth factors leading to complications with bone production. The disorder affects 1 in 27,500 people. Individuals affected with achondroplasia have dwarfism with short arms and legs, an enlarged head, and a prominent forehead. The defective gene for achondroplasia is located on the short arm of chromosome 4 at position 16.3.
A man (♂) with both DMD and achondroplasia genetic disorders marries a wild-type phenotype woman (♀) with neither disorder. The father (♂) of the woman has the DMD genetic disorder,but mother (♀) of the woman does not. The mother (♀) of the man is wild-type phenotype and does not have the achondroplasia genetic disorder.
Reminder: DMD is X-linked recessive and achondroplasia is autosomal dominant.
What fraction of their daughters (♀) will have both DMD and achondroplasia genetic disorders?

• None, 0%
• 1/4, 25%
• 1/2, 50%
• 3/4, 75%
• All, 100%

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Patterns of Inheritance Analysis from Pedigree Charts

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◼		⬤		◯		◻		◻		⬤
◻	⬤	⬤		◻		◯		◼	◻	◻
◯		◻		◻		⬤	◻	⬤		◻
◻	◯	◯	◼	◻	⬤	◯	◯	⬤	◻	◻

 
Examine the pedigree above. Which one of the following patterns of inheritance is most likely demonstrated in the above pedigree inheritance?

• autosomal dominant
• autosomal recessive
• x-linked dominant
• x-linked recessive
• y-linked

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Pedigree Analysis for Inheritance Types

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Match the following pedigrees to their most likely inheritance type.
Note: each inheritance type will only be used ONCE.

	Your Choice	Prompt
	Drop Your Choice Here	1. ⬤ ◻   ◯ ◻   ◯ ◼     ◻ ⬤ ◼ ◯   ◯ ◼ ◻ ◯           ◻ ⬤   ◯ ◻   ◼ ⬤ ◻ ◼ ◯ ◻ ◻ ◯ ◻ ⬤ ◼ ⬤ ◻
	Drop Your Choice Here	2. ◻ ⬤   ◻ ◯   ◻ ◯     ◯ ◻ ◯ ◻   ◯ ◼ ◻ ◯           ◯ ◻   ◯ ◻   ◯ ◻ ◻ ◻ ◯ ⬤ ◻ ◯ ◼ ◻ ◯ ◻ ◻
	Drop Your Choice Here	3. ⬤ ◻   ◻ ◯   ⬤ ◼     ◻ ◻ ◼ ◯   ◻ ⬤ ⬤ ◻           ◻ ⬤ ◻ ⬤ ◻   ◻ ◯ ◻ ◻ ⬤ ◯ ◯ ⬤ ◻ ◼ ◯ ◯ ◻
	Drop Your Choice Here	4. ◼ ◯   ◯ ◻   ◻ ⬤     ◯ ◻ ◯ ◻   ◯ ◼ ◯ ◼           ◯ ◻   ◼ ◯   ◻ ◯ ◯ ◯ ◻ ⬤ ◯ ◼ ◻ ◼ ◻ ◯ ◻
	Drop Your Choice Here	5. ◯ ◻   ◼ ◯   ◯ ◻     ◯ ◯ ◻ ◯   ◼ ◯ ◻ ◯           ◯ ◻   ◯ ◼   ◼ ◯ ◻ ◯ ◻ ◯ ◼ ◯ ◼ ◼ ◯ ◼ ◯

Drag one of the choices below:

• A. y-linked
• B. autosomal recessive
• C. x-linked dominant
• D. x-linked recessive
• E. autosomal dominant

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X-Linked Inheritance Patterns in Fruit Flies

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The white-eyed phenotype is an X-linked recessive disorder in fruit flies. The red allele, +, is dominant to the white allele, w. The offspring of size 480 from the mating of a single female and a single male are shown in the table below:

phenotype	female ♀	male ♂
red-eyed (wildtype)	239	0
white-eyed (mutant)	0	241

What are the genotypes of the parents in this cross?

• heterozygous female (+w) and mutant male (w–)
• homozygous mutant female (ww) and wildtype male (+–)
• homozygous mutant female (ww) and mutant male (w–)
• heterozygous female (+w) and wildtype male (+–)
• homozygous wildtype female (++) and male of unknown genotype

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Probability of Specific Gender Distribution in Offspring

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A woman has six (6) children, what is the probability that she has exactly two (2) boys and four (4) girls?

• ( 6 ) 2

  (¾)2⋅(¼)4

  =

  6!   (6–2)! ⋅ 2!

  (¾)2⋅(¼)4

  =

  6⋅5⋅4⋅3   2

  ×

  32   4244

  =

  15×9   4096

  =

  0.0330

  =

  3.3%

• ( 6 ) 2

  (¼)2⋅(¾)4

  =

  6!   (6–2)! ⋅ 2!

  (¼)2⋅(¾)4

  =

  6⋅5⋅4⋅3   2

  ×

  34   4244

  =

  15×81   4096

  =

  0.2966

  =

  29.7%

• ( 4 ) 4

  (½)4⋅(½)2

  =

  4!   (4–4)! ⋅ 4!

  (½)4

  =

  1   1

  ×

  1   24

  =

  1   64

  =

  0.0156

  =

  1.6%

• ( 4 ) 2

  (½)2⋅(½)4

  =

  4!   (4–2)! ⋅ 2!

  (½)4

  =

  4⋅3   2

  ×

  1   24

  =

  6   64

  =

  0.0938

  =

  9.4%

• ( 6 ) 2

  (½)2⋅(½)4

  =

  6!   (6–2)! ⋅ 2!

  (½)6

  =

  6⋅5⋅4⋅3   2

  ×

  1   26

  =

  15   64

  =

  0.2344

  =

  23.4%

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