Chromosome Variation Part 2

how does aneuploidy arise

• chromosome is lost

• Robertsonian translocation

• nondisjunction (most common way ___ ____)

aneuploidy in humans

• more than 30-50% of human embryos are spontaneously aborted (miscarried)

  • Before 20 weeks gestation

• most aneuploidy due to maternal nondisjunction

• sex chromsomes

  • more common

  • XO, XXY, XXX, XYY

autosomes

• rare

  • Down syndrome (Trisomy 21) - 1 in 700

  • Edward syndrome (Trisomy 8) - 1 in 8000

  • Patau syndrome (Trisomy 13) - 1 in 15000

Down syndrome

• most common aneuploidy in humans

  • 92% Primary, 4% Familial (Translocation), Mosaic

• The incidence of primary _____ increases with material age

Primary Down syndrome

• not heritable

• nondisjunction

• chromosome 21

Familial Down syndrome

• heritable

• Robertosonain Transolcation

• chromosome 14 & 21

polyploidy

more than two complete sets of chromosomes

types of polypoidy

• autopolyploid

• allopolyploid

autopolypoidy

• multiple sets of chromosomes from the same species

• homologous chromosomes can’t pair

• unbalanced gametes

  • most ____ are sterile

allopolyploidy

• result from a hybrid between different species

• to be able to propagate (reproductive via gametes)

• hybridization

• hybrid doubles genome thru nondisjunction ALL chromosomes

seedless fruit

• these are sterile and grow larger

  • resources not allocated toward reproduction

selective breeding

• triploid salmonids

• grow larger

• escapees won’t reproduce