Variation in individual chromosome number: Aneuploidy not generally well-tolerated in animals; primarily detected after spontaneous abortion. Sex chromosome aneuploidy occurs more often than autosome aneuploidy (inactivation of X compensates). Four main types of aneuploidy: Nullisomy = loss of one homologous chromosome pair. Monosomy = loss of a single chromosome. Trisomy = one extra chromosome. Tetrasomy = one extra chromosome pair.

Fig. 16.11, Examples of aneuploidy.

Variation in individual chromosome number: Down Syndrome (trisomy-21, OMIM-190685): Occurs in 1/286 conceptions and 1/699 live births. Probability of non-disjunction trisomy-21 occurring varies with age of ovaries and testes. Trisomy-21 also occurs by Robertsonian translocation  joins long arm of chromosome 21 with long arm of chromosome 14 or 15. Familial down syndrome arises when carrier parents (heterozygotes) mate with normal parents. 1/2 gametes are inviable. 1/3 of live offspring are trisomy-21; 1/3 are carrier heterozygotes, and 1/3 are normal.

Segregation patterns for familial trisomy-21 Fig. 16.18 14 14 21 21 Trisomy Inviable Carrier Normal Fig. 16.19, Segregation patterns for familial trisomy-21

Relationship between age of mother and risk of trisomy-21: 16-26 7.7/10,000 27-34 4/10,000 35-39 ~3/1000 40-44 1/100 45-47 ~3/100

Trisomy-13 - Patau Syndrome 2/10,000 live births Trisomy-18 - Edwards Syndrome 2.5/10,000 live births

http://dish. andrewsullivan http://dish.andrewsullivan.com/2015/01/15/the-politics-of-fertility-fog-ctd-2/

http://food-hacks. wonderhowto http://food-hacks.wonderhowto.com/how-to/tell-if-your-expired-eggs-are-still-good-eat-0154309/

Variation in complete sets of chromosomes: Monoploidy = one of each chromosome (no homologous pair) Polyploidy = more than one pair of each chromosome. Fig. 16.22

Variation in complete sets of chromosomes: Monoploidy and polyploidy: Result from either (1) meiotic division without cell division or (2) non-disjunction for all chromosomes. Lethal in most animals. Monoploidy is rare in adult diploid species because recessive lethal mutations are expressed. Polyploidy tolerated in plants because of self-fertilization; plays an important role in plant speciation and diversification. Two lineages of plants become reproductively isolated following genome duplication, can lead to instantaneous speciation. Examples include 15% of angiosperm speciation events 31% of ferns crops like canola, wheat, cotton

Viable Self-fertile

http://www.sbs.utexas.edu/levin/bio213/evolution/speciation.html

Odd-numbered polyploids have unpaired chromosomes and usually are sterile. Most seedless fruits we eat are triploid.