Ch.8: Variation in Chromosome Structure and Number Flashcards
Cytogenetics
involves the microscopic examination of chromosomes
What are the 3 main features cytogeneticists use to identify and classify chromosmes?
location of centromere (where the duplication process happens), size, banding pattern
What are the different centromeric locations on the chromosome?
Metacentric: centromere is near the middle
Submetacentric: centromere is slightly off center
Acrocentric: centromere is significantly off center but not at the end
Telocentric: centromere is at one end
Explain Banding Patterns
Chromosomes are exposed to the Giemsa dye (developed by Gustav Giemsa) to differentiate similarly sized chromosomes or detect chromosomal changes
What are the two types of changes that can occur in chromosome structure?
Deletions and Duplications: The total amount of genetic material in the chromosome can change
Inversions and Translocation: The total amount of genetic material remains the same, but is rearranged
What are the 2 types of deletion?
Terminal Deletion: When a chromosome breaks into two pieces due to a single
break, the part without the centromere is eventually lost
Interstitial Deletion: When a chromosome breaks in two places, the central
fragment is lost, and the two outer pieces reattach
What are homologous genes? What are paralogs?
Homologous genes – genes that are derived form a single ancestral gene
Paralogs - homologous genes within a single species
What is the difference between myoglobin and hemoglobin?
Myoglobin stores oxygen in muscle cells
Hemoglobin bind and transport oxygen via red blood cells and
provide different functionalities corresponding to the oxygen needs of the embryo, fetus and adult
Comparative genomic hybridization (CGH) to detect chromosomal deletions and duplications
Developed by Kallioniemi and Pinkel as a tool to
detect chromosomal deletions and duplications in human cancer ; found Because the probes from the cancer cells fluoresce green and the probes from the normal cells fluoresce red,
the fluorescent differences can be used to detect whether a deletion or duplication has occurred
Chromosomal Inversion
occurs when a segment of the chromosome flips to the opposite orientation
What are the 2 types of Chromosomal Inversion? Which one can cause greater abnormalities?
Pericentric inversion: includes the centromere
Paracentric inversion: does not include the centromere;
paracentric
Chromosomal Translocation
the total amount of genetic material is not altered - can be caused by chromosomal breakage and DNA repair or nonhomologous crossovers
An individual that caries a balanced translocation produces?
both normal and abnormal gametes and when mating
occurs with a normal individual the offspring can be normal, or harbor (syndromes) balanced or unbalanced (lethal) chromosomes
What 2 ways can chromosome #s vary?
Euploidy: Variation in the number of complete sets of chromosome
Aneuploidy: Variation in the number of particular chromosomes within a set (commonly causes an abnormal phenotype)
What happens with aneuploid conditions in humans?
- 50% of spontaneous abortions are due to such abnormalities, but in some cases, produces an offspring that can survive
-aneuploidies involving sex chromosomes generally have less severe effects than those of autosome
-Pseudoautosomal genes- genes that are found on the X or Y sex chromosomes that act the same as
autosomal gene
What is Down Syndrome caused by?
the failure of chromosome 21 to segregate properly, most commonly occurring during meiosis I in oocyte
Describe variations in euploidy amongst multicellular organisms
generally not common in animals, but there are exception
Ex. Liver cells, Some related species of frogs are diploid or tetraploid, and Variation in euploidy is common in insects.
What are the 3 natural mechanisms that cause the chromosome number to vary?
meiotic nondisjunction, mitotic nondisjunction, interspecies crosses
Nondisjunction
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate
normally during nuclear division
- usually resulting in an abnormal distribution of chromosomes in the daughter nuclei
- meiosis I is more severe than meiosis II
What are the 3 ways the number of chromosome sets in a given individual/species can vary?
Autopolyploidy, Alloploidy, Allopolyploidy
Autopolyploidy
increase in the number of sets within a single species
Alloploidy
the combining of chromosome sets from different species
Allopolyploidy
when the number of chromosome sets increases in an alloploid