Lecture 14

Question 1

Modifications at level of chromosome

Answer 1

phenotypic variations result from changes of individual genes

Question 2

chromosome mutations and aberrations

Answer 2

1. total number of chromosomes vary
2. deletion
3. duplication
4. rearrangement

Question 3

Variations from two haploid sets - chromosome mutations/aberrations

Answer 3

• change in total number of chromosomes
• deletion of duplication of genes/segments
  of chromosomes
• rearrangement of genetic material within or among chromosomes

Question 4

Aneuploidy

Answer 4

• variations in chromosome numbers
• organism gains or loses one or more chromosomes
• 2n + x chromosomes

Question 5

Monosomy

Answer 5

loss of single chromosome in diploid genome
- 2n-1

Question 6

Trisomy

Answer 6

gain of single chromosome
-2n+1

Question 7

Euploidy

Answer 7

complete haploid sets of chromosomes are present
- multiples of n

Question 8

Polyploidy

Answer 8

more than 2 sets of chromosomes are present
- 3n,4n,5n

Question 9

Triploid

Answer 9

three sets of chromosome are present
- 3n

Question 10

nondisjunction

Answer 10

• gives rise to chromosomal variation
• paired homologs fail to disjoin (separate) during segregation
• nondisjunction can occur during meiosis I or II

Question 11

monosomy

Answer 11

• loss of one chromosome
• produces 2n-1 complement
• although one copy remains, if copy is lethal, organism is not viable
• monosomy unmasks recessive lethals

Question 12

haploinsufficiency

Answer 12

when one copy is insufficient for organism to survive- lethal

Question 13

Trisomy

Answer 13

• 2n+1 chromosomes
• addition of chromosome produces more viable organisms
• trisomies for autosomes are often lethal
• plant trisomies are viable: phenotype altered
• down syndrome

Question 14

DSCR: Down syndrome critical regions

Answer 14

• critical region of chromosome 21
• genes are dosage sensitive
• responsible for many phenotypic-associated syndromes

Question 15

origin of extra 21st chromosome

Answer 15

• nondisjunction of chromosome 21 during meiosis
• homologs do not disjoin in anaphase I or II
• leads to n+1 gametes
• ovum is the source of 95 percent of trisomy cases (increased incidence with increasing maternal age)

Question 16

translocation of chromosome 21

Answer 16

down syndrome occasionally runs in families
- translocate onto chromosome 14

Question 17

Patau syndrome

Answer 17

trisomy 13
- survive to term
- manifest severe malformations and early lethality

Question 18

Edwards syndrome

Answer 18

trisomy 18
- survive to term
- manifest severe malformations and early lethality

Question 19

trisomies

Answer 19

often found in spontaneously aborted fetuses

Question 20

autosomal monosomies…

Answer 20

are seldom found, suggest monosomic gametes may be functionally impaired

Question 21

polyploidy

Answer 21

• more than 2 multiples of haploid chromosomes found
• triploid 3n
• tetraploid 4n
• pentaploid 5n

Question 22

origin of polyploidy

Answer 22

• addition of one or more sets of chromosomes identical to the haploid complement of same species (autopolyploidy)
• combination of chromosome sets from different species as a consequence of hybridization (allopolyploidy)