Then consider the segregation possibilities for each set! ??? Downloaded by Nat Kp ([email protected]) lOMoARcPSD|2850388
Allopolyploidy: result of crosses between 2 or more species, chromosomes of these plants are di ff erent and their ploidy is best described as 1+1, allopolyploids cannot produce gametes and reproduce asexually Autopolyploidy: produced by duplication of the chromosomes of the plant • if the original plant is allopolyploid 1+1 then a 2n plant is produced (2 copies of each chromosome) • if the original plant is not allopolyploid then a 4n plant is produced • autopolyploids usually exhibit better growth but less seed production Polyploids produced by chromosome doubling in interspecific hybrids may be fertile if their constituent genomes segregate independently. Interspecies crossing of animals can create viable progeny - like allopolyploid mules - but: Donkey (2n = 62, n = 31) x Horse (2n = 64, n = 32) = Mule (2n = 63), and o ff spring cannot perform meiosis because there is unequal distribution of paternal and maternal genetic material. The mule cannot undergo autopolyploidy - chromosome doubling is not well tolerated in animals. Week 3 Lecture 6 Endomitosis • chromosome replication and separation of sister chromatids without cell division - produces polyploid tissues like muscles (multiple nuclei) Polytene chromosomes • chromosome replication but no separation of sister chromatids - homologous polytene chromosomes pair, centromeres congeal into a chromocentre - creates a high level of expression eg. polytene chromosomes of drosophila exist in the larval stage, are discarded with development Aneuploidy: diploid genome which lacks a chromosome or has an extra chromosome, can be caused by meiotic nondisjunction 2n + 1 trisomies - gamete has an extra chromosome 2n - 1 monosomies - gamete has one less chromosome Nondisjunction in meiosis I results in 2 diplo and 2 nullo gametes Nondisjunction in meiosis II results in 2 normal , 1 diplo , 1 nullo gametes Meiotic nondisjunction in humans: • autosomal monosomies lost early in pregnancy • 3 autosomal trisomies are seen as live births: trisomy 21 (Down syndrome) (pleiotropic e ff ect) trisomy 13 (Patau syndrome) trisomy 18 (Edwards syndrome) *A utosome is any of the numbered chromosomes, as opposed to the sex chromosomes* Downloaded by Nat Kp ([email protected]) lOMoARcPSD|2850388
Aneuploid conditions in sex chromosomes: *note that X is inactivated in the presence of another X, alteration of character still in e ff ect because the additional X reactivated during development - involved in hormone production* X0 Turner Syndrome , F, subdued female character - short stature, wide- chested, normal IQ, webbing of neck, ovaries fail to develop, uterus and oviducts can be small and immature Treatment: growth hormone therapy to increase stature, estrogen for breast development XXY Klinefelter Syndrome , M, subdued male character - phenotypic features develop after puberty, breast development, female body fat distribution Treatment: testosterone therapy, breast tissue removal XXX Triple X Syndrome, F, excess female character XYY Double Y Males, M, excess male character
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