Non-disjunction and chromasomal abnormalities Flashcards
Chromosomal abberrations
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
Aneuploidy
An organism gains or loses one or more chromosomes but not a complete set
Monosomy
loss of a single chromosome in diplod genome
Trisomy
Gain of one chromosome in diploid genome
Euploidy
Complete haploid sets of chromosomes present
includes:
-Polyploidy
-triploid
-Teraploid
Polyploidy
More than two sets of chromosomes
Triploid
3 sets of chromosomes
tetraploid
4 sets of chromosomes
Kleinfeter syndrome
Gain of an X chromosome (47, XX)
Turner syndrome
Loss of an X chromosome (45, X)
Tolerable sex C syndromes
Femals can have extra X chromosomes
Males can contain AN extra Y chromosome
Monosomy in autosomes
Monosomy is lethal for any of the autosomes- not tolerated in humans or other animals
Monosomy in Drosophilia
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
Monosomy lethality
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
Trisomy
Addition of chromosome-produces somewhat viable individuals in animal and plant species compared to a loss of a chromosome
Trisomy in animals
Chromosome is usually small, addition of a large autosome is usually lethal
Trisomy in plants
Trisomic individuals are viable but have altered phenotype
E. Trisomy in plants
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
Down syndrome cause
Trisomy 21
-Only human autosomal trisomy where significant number of individuals survive longer than a year past birth
Discovery + Occurence of Down syndrome
Discovered in 1866 by Langdon Down
Found in 1 infant in every 800 live births (USA) and 1 in every 500 live births (SA)
Phenotype of Down syndrome
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
Region of Down Syndrome
Down syndrome Critical Region (DSCR)- portion of chromosome 21 responsible for down syndrome (still being studied)
Human aneuploidies that survive to term
-Down syndrome
-Patau syndrome (47, 13+)
-Edwards syndrome ( 47, 18+)
-No monosomies survie to term
Studies on spontaneously aborted fetuses
-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
origination of polyploidy
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
Autotriploids
Failure of all chromosomes to seperate during mitotic division, fertilised by haploid gamete.
Two sperm fertilise an ovum
Autotetraploids
Chromosome duplication without cell divison
Allopolyploidy
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
