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Lecture 21 – Aberrant Ploidy I. Aberrant euploidy A. examples of differing ploidy monoploid 1x diploid 2x triploid 3x tetraploid 4x

pentaploid 5x hexaploid 6x octaploid 8x

B. in nature - in plants (and less commonly, animals) – 30 – 35% of naturally occurring plant

species are polyploid. - endopolyploidy – in many animals, some cells may be polyploid II. Monoploidy – 1n, rare result of errors in cell division A. Usually sterile B. in some species, some individuals are monoploid - males in social insects (ants, bees, wasps) - males produced by parthenogenesis - not sterile because C. useful experimentally and in agriculture - experimental use of monoploidy - but how do you get back to diploid?

diploidplant

meiotic productcells plated

haploidembryoids

grow haploidplantletsmonoploid

plantdiploidplant

diploidembryoids

grow diploidplantlets

monoploidplant(sterile)

treatwithcolchicine

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III. Polyploids (odd vs. even chromosome #) A. Odd ploidies 1. origins of triploid

- odd ploidies are generally sterile

- why?

- triploidy can be very useful? B. Even ploidies and cell divisions - most natural polyploids are even in # homologues (i.e. 2x, 4x, 6x, 8x, etc) IV. Auto vs allopolyploids A. major types 1. autopolyploid 2. allopolyploid - homeologous

A1 A2 A3

A1 A2 A3

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B. autopolyploid

- endoreduplication C. allopolyploidy

D. experimental allopolyploidy’ - way of producing useful plant varieties

2n 0n

0n 0n

2n 2n

meiosis

2n

4n

mitosisA1A1

A2 A2

A1A1

A2

A2

0n

2n

A1A1

A2 A2

A1A1

A2 A2

A1A1 A2A2

tall fescue Italian ryegrassisolate cells

remove cell wall

fuse protoplasts

heterokaryon

hybrid cell

regenerate plant

plant has characteristicsintermediate betweentwo parentsallotetraploid

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IV. Aneuploidy A. polysomy 1. trisomy a. consequences b. human trisomies (most are inviable) - Klinefelter (XXY) - trisomy 21 (Down syndrome) - trisomy 13 (Patau syndrome) - trisomy 18 (Edwards syndrome) 2. monosomy a. human monosomies B. aneuploidy arises because of nondisjunction during meiosis

BB

AA

a a

bb

BBbb

a a

b

A

b

A

B B

a a

AA