Ch.8: Variation in Chromosome Structure and Number

Question 1

Cytogenetics

Answer 1

involves the microscopic examination of chromosomes

Question 2

What are the 3 main features cytogeneticists use to identify and classify chromosmes?

Answer 2

location of centromere (where the duplication process happens), size, banding pattern

Question 3

What are the different centromeric locations on the chromosome?

Answer 3

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

Question 4

Explain Banding Patterns

Answer 4

Chromosomes are exposed to the Giemsa dye (developed by Gustav Giemsa) to differentiate similarly sized chromosomes or detect chromosomal changes

Question 5

What are the two types of changes that can occur in chromosome structure?

Answer 5

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

Question 6

What are the 2 types of deletion?

Answer 6

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

Question 7

What are homologous genes? What are paralogs?

Answer 7

Homologous genes – genes that are derived form a single ancestral gene
Paralogs - homologous genes within a single species

Question 8

What is the difference between myoglobin and hemoglobin?

Answer 8

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

Question 9

Comparative genomic hybridization (CGH) to detect chromosomal deletions and duplications

Answer 9

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

Question 10

Chromosomal Inversion

Answer 10

occurs when a segment of the chromosome flips to the opposite orientation

Question 11

What are the 2 types of Chromosomal Inversion? Which one can cause greater abnormalities?

Answer 11

Pericentric inversion: includes the centromere
Paracentric inversion: does not include the centromere;
paracentric

Question 12

Chromosomal Translocation

Answer 12

the total amount of genetic material is not altered - can be caused by chromosomal breakage and DNA repair or nonhomologous crossovers

Question 13

An individual that caries a balanced translocation produces?

Answer 13

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

Question 13

What 2 ways can chromosome #s vary?

Answer 13

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)

Question 13

What happens with aneuploid conditions in humans?

Answer 13

• 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

Question 14

What is Down Syndrome caused by?

Answer 14

the failure of chromosome 21 to segregate properly, most commonly occurring during meiosis I in oocyte

Question 15

Describe variations in euploidy amongst multicellular organisms

Answer 15

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.

Question 16

What are the 3 natural mechanisms that cause the chromosome number to vary?

Answer 16

meiotic nondisjunction, mitotic nondisjunction, interspecies crosses

Question 17

Nondisjunction

Answer 17

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

Question 18

What are the 3 ways the number of chromosome sets in a given individual/species can vary?

Answer 18

Autopolyploidy, Alloploidy, Allopolyploidy

Question 19

Autopolyploidy

Answer 19

increase in the number of sets within a single species

Question 20

Alloploidy

Answer 20

the combining of chromosome sets from different species

Question 21

Allopolyploidy

Answer 21

when the number of chromosome sets increases in an alloploid