large scale chap 17
Basic Terminology and Types of Chromosome Variants
Q: What is a haploid organism?
A: It has a single complete set of chromosomes (n), typically found in gametes.
Q: What is a diploid organism?
A: It has two complete sets of chromosomes (2n), one from each parent.
Q: Define monoploid.
A: An organism from a normally diploid species that possesses only one set of chromosomes (n).
Q: What is a polyploid?
A: An organism with more than two sets of chromosomes. Examples include plants like tobacco and grapes.
Q: Differentiate between autopolyploids and allopolyploids.
A:
Autopolyploids: Multiple sets of chromosomes from the same species.
Allopolyploids: Chromosome sets from two or more species.
Formation of Polyploids and Chromosome Structure Changes
Q: How are triploids (3n) created, and why are they usually sterile?
A: Triploids result from crossing tetraploids (4n) with diploids (2n). They are sterile due to incomplete sets of chromosomes (aneuploid gametes).
Q: What chemical can induce tetraploidy?
A: Colchicine, which disrupts microtubule polymerization during cell division.
Q: Define aneuploidy.
A: A condition where the chromosome number deviates from the normal by part of a chromosome set (e.g., 2n+1 or 2n-1).
Q: List types of chromosomal rearrangements.
A: Deletions, duplications, inversions, and translocations.
Effects of Chromosome Variants on Meiosis
Q: What issues arise during meiosis in triploids?
A: Formation of aneuploid gametes leads to sterility.
Q: Why are tetraploids often fertile?
A: Functional 2n gametes can form due to pairing between homologous chromosomes.
Q: What is the consequence of a paracentric inversion during meiosis?
A: It can result in deletion products.
Q: What is a diagnostic feature of a reciprocal-translocation heterozygote?
A: A 50% reduction in viable gametes or zygotes.
Impact of Chromosome Number Variants on Humans
Q: What causes Down syndrome?
A: Trisomy of chromosome 21 (2n+1).
Q: Why are aneuploids more abnormal than polyploids?
A: Gene dosage imbalance disrupts normal development.
Q: Give an example of a sex chromosome aneuploidy.
A: Turner syndrome (XO) or Klinefelter syndrome (XXY).