Non-disjunction and chromasomal abnormalities

Question 1

Chromosomal abberrations

Answer 1

Alterations of the precise diploid content of chromosomes including:
-Change in total chromosome number
-Deletion or duplication of chromosomal segments
-Rearrangements of the genetic material within or among chromomsomes

Question 2

Aneuploidy

Answer 2

An organism gains or loses one or more chromosomes but not a complete set

Question 3

Monosomy

Answer 3

loss of a single chromosome in diplod genome

Question 4

Trisomy

Answer 4

Gain of one chromosome in diploid genome

Question 5

Euploidy

Answer 5

Complete haploid sets of chromosomes present
includes:
-Polyploidy
-triploid
-Teraploid

Question 6

Polyploidy

Answer 6

More than two sets of chromosomes

Question 7

Triploid

Answer 7

3 sets of chromosomes

Question 8

tetraploid

Answer 8

4 sets of chromosomes

Question 9

Kleinfeter syndrome

Answer 9

Gain of an X chromosome (47, XX)

Question 10

Turner syndrome

Answer 10

Loss of an X chromosome (45, X)

Question 11

Tolerable sex C syndromes

Answer 11

Femals can have extra X chromosomes
Males can contain AN extra Y chromosome

Question 12

Monosomy in autosomes

Answer 12

Monosomy is lethal for any of the autosomes- not tolerated in humans or other animals

Question 13

Monosomy in Drosophilia

Answer 13

Flies monosomic for chromosome IV
-less than 5% of organism’s genome
-Develp more sloly, have smaller body size, impaired variability
-Monosomy for larger chromosomes is lethal as no flies with this genotype have evr recovered

Question 14

Monosomy lethality

Answer 14

lethal alleles- Unpaired condition results in death of organism
Haploinsufficiency- single copy insufficient to provide adequate funcion to sustain organism
Monosomy for autosomes present in maize, tobacco, the evening primrose and other plants is not lethal but less viable than diploid derivatives

Question 15

Trisomy

Answer 15

Addition of chromosome-produces somewhat viable individuals in animal and plant species compared to a loss of a chromosome

Question 16

Trisomy in animals

Answer 16

Chromosome is usually small, addition of a large autosome is usually lethal

Question 17

Trisomy in plants

Answer 17

Trisomic individuals are viable but have altered phenotype

Question 18

E. Trisomy in plants

Answer 18

Jimson weed (Datura): n=12
12 possible trisomies lead to altered fruit capsule phenotypes as there are viable trisomies of every chromosome for this specific plant

Question 19

Down syndrome cause

Answer 19

Trisomy 21
-Only human autosomal trisomy where significant number of individuals survive longer than a year past birth

Question 20

Discovery + Occurence of Down syndrome

Answer 20

Discovered in 1866 by Langdon Down
Found in 1 infant in every 800 live births (USA) and 1 in every 500 live births (SA)

Question 21

Phenotype of Down syndrome

Answer 21

12-14 characterisitcs in Down syndrome
An individual only expresses 6 to 8 of them
Outward appearance is similar:
-Epicanthic fold in each eye, flat face, round head
-Short, protruding, furrowed tongue, short broad hands
-Physical, psychomotor and mental development is retarded, poor muscle tone
-Shorter life expectancy ( approxiamtely 50 years), some people have lived into their 60s

Question 22

Region of Down Syndrome

Answer 22

Down syndrome Critical Region (DSCR)- portion of chromosome 21 responsible for down syndrome (still being studied)

Question 23

Human aneuploidies that survive to term

Answer 23

-Down syndrome
-Patau syndrome (47, 13+)
-Edwards syndrome ( 47, 18+)
-No monosomies survie to term

Question 24

Studies on spontaneously aborted fetuses

Answer 24

-20% of all conceptions terminate in spontaneous abortion
-30% of all sponataneously aborted fetusts demonstrate a chromomsomal imbalance
-Therefore, 6% of conceptions contain abnormal chromosome compliments, mainly of which is aneuploid

Question 25

origination of polyploidy

Answer 25

Can originate in 2 ways:
autopolyploidy- The addition of one or more sets of chromosomes identical to the normal haploid compliment of same species
Allopolyploidy- The combination of chromosomes sets from different species occuring due to hybridisation

Question 26

Autotriploids

Answer 26

Failure of all chromosomes to seperate during mitotic division, fertilised by haploid gamete.
Two sperm fertilise an ovum

Question 27

Autotetraploids

Answer 27

Chromosome duplication without cell divison

Question 28

Allopolyploidy

Answer 28

Hybridizing two closely related species. Ovum from species wit chromosome set AA fertilised with sperm from species with chromosomes BB, result in AB hybrid.
Chromosomes cant fuse so may be sterile