Variation in Chromosome Number and Structure
Objectives:
After completing this section, students should:
1. be familiar with basic chromosome morphology.
2. describe ways in identifying and distinguishing chromosomes.
3. understand how changes in chromosome number arise, as well as how
such changes lead to genetic defects.
4. be able to distinguish between four major types of chromosome structural
aberrations: (deletions, duplications, inversions, translocations).
Key Terms:
karyotype
centromere
telocentric
acrocentric
metacentric
satellite
histones
dicentric
deletion
duplication
inversion
translocation
polyploidy (auto- and allo-)
trisomy
nondisjunction
Online Lesson(s):
None
haploid
tetraploid
cytogenetics
Chromosome Morphology
Karotype =
Morphology =
Morphology is based on:
1)
2)
3)
4)
Names for describing chromosomes with different centromere
positions:
Metacentric
Acrocentric
Telocentric
Dicentric
Chromosome banding patterns are produced by:
Evolutionary conservation of chromosomes:
Variation in Chromosome Number and Structure
Normal Pattern studies so far…
1)
Each chromosome represented
once in gametes
twice in zygotes
2)
Each gene at a specific locus, the loci on a chromosome in a constant and
definite linear order.
Now we will study changes in the regular patterns.
Types of Chromosome Changes
1) Structural changes / Modifications within a chromosome:
Inversions:
Translocations:
2) Modifications in amount of chromosomes
Sets______________________
1…. Haploid
2…. Diploid
3….
4….
6….
8….
Single_____________________
2n – 1 ---- Monosomic
2n + 1 ---- Trisomic
2n=
n=
Autopolyploids
Chromosomes Replicate: Diploid
2n = 4
Chromatids separate
but cell does not divide
Resulting Cell: Autotetraploid
2n = 8
2n + 2n = 4 + 4
Polyploidy
Widespread in the plant kingdom, rare in animals
Why?
Polyploid plant species:
Diploid Alfalfa
2n = 16
Wheat
Oats
Triticale
Alfalfa
Switchgrass
Potato
Cotton
Coffee
Banana
Iris
Cultivated Alfalfa
2n = _______ __________ploid