Chromosomes 2

Class Announcements

  • Quiz View Scores: Reintroduced; ensure questions are open-ended for better scores.

  • Curiosity Scores: Important for improving overall performance; refer back to materials.

  • Due Dates: All materials due by Tuesday or Sunday.

  • Upcoming Schedule:

    • Monday: Review day before the exam on Wednesday. Last material covered on Friday.

Chromosome Changes Overview

  • Focus of today's lecture: Aneuploidy.

  • Last class covered euploidy: Changes in entire chromosome sets.

  • Today: Changes in single chromosomes and potentially parts of chromosomes.

Chromosome Structure

  • Standard Chromosome Structure: Comprised of a centromere in the middle, with a p arm (upper) and q arm (lower).

  • Changes: Can lose or gain parts, either completely or partially (p or q arm).

Aneuploidy Explained

  • Definition: Change in the number of chromosomes, focusing on single chromosomes.

  • Two scenarios:

    • Monosomy: Loss of one chromosome (2n - 1).

    • Trisomy: Gain of one chromosome (2n + 1).

  • Examples of Sex Chromosome Changes:

    • XXY (extra X), XYY (extra Y), XXX (extra X), or X0 (missing X).

Forms of Aneuploidy

  • Full form: Every cell in the organism shows the chromosomal abnormality; results from events very early in development.

  • Partial form: Not losing the entire chromosome, but part of it; typically less severe.

  • Mosaic form: Abnormalities arise later in development, affecting certain tissues only, generally less severe than full form.

Causes of Aneuploidy

  • Normal chromosome separation (disjunction) during cell division is crucial; can be disrupted leading to nondisjunction.

  • Nondisjunction: Failure of chromosomes to separate properly, resulting in either gamete with missing or extra chromosomes.

Monosomy Details

  • Typically lethal in autosomes (chromosomes 1-22) when missing an entire chromosome.

  • Turner's Syndrome (XO): Not lethal; symptoms include shorter stature and sterilization.

Trisomy Details

  • Common Trisomies:

    • Trisomy 16: Most common but often results in miscarriage.

    • Edwards Syndrome (Trisomy 18): Severe, always results in early death.

    • Down Syndrome (Trisomy 21): Common chromosomal abnormality, wide range of symptoms.

      • Characteristic features include flat face and slanted eyes.

      • Maternal age is a risk factor; the risk increases with age.

Allosomal Trisomy Statistics

  • Klinefelter Syndrome (XXY): Generally asymptomatic in males, may experience reduced testosterone.

  • Jacobs Syndrome (XYY): Typically asymptomatic; associated with slight learning disabilities.

  • Triple X Syndrome (XXX): Generally asymptomatic; physical stature may be taller.

Important Takeaways

  • Aneuploidy vs. Euploidy: Aneuploidy causes specific phenotypic changes due to gene imbalance, which is often more severe than euploidy.

  • Gene Balance: Essential for normal development; disruptions in genetic material can lead to physiological imbalances.

  • Full sets of chromosomes (euploidy) do not typically occur as commonly in animals as they do in plants due to stability.

Chapter Summary

  • Euploidy: Changes in entire sets, typically involves complete sets of chromosomes and does not show significant phenotypic impact.

  • Aneuploidy: Changes regarding individual chromosomes; likely to influence organism development leading to observable physical changes.