BISC 202 chromosomes and genetic information (W9-10)

what are the two types of mutations affecting the number of chromosomes?

euploidy and aneuploidy

euploidy

aneuploidy

natural causes of monoploidy

artificial causes of monoploidy

effects of monoploidy on survival and phenotype

effects of monoploidy on reproduction

why are monoploids almost always sterile

unless the gamete is lucky enough to get every chromosome (during meiosis I) it will be missing one or more chromosomes, and the resulting offspring will usually not survive

which events can contribute to the formation of a tetraploid cell?

how do tetraploids compare to normal diploids, in plants?

tetraploids are fertile and have larger size/yields

types of polyploidy with >2n

autopolyploid and allo(amphi)polyploid

autopolyploid

a polyploid created by the multiplication of one basic set of chromosomes (in one species)

allo(amphi)polyploid

an individual that has 2 or more sets of genetically distinct chromosomes, made by hybridization of two different species

effects of allopolyploidy examples

allotetraploid

mix of the DNA of two different species

triploidy

when the odd number of chromosome sets (one extra set of chromosomes as in 3n) is present

how would you make triploid plant?

why would agricultural scientists make a triploid plant?

the triploid plant can be hardier and have higher yield than the diploid plants

triploid plants are sterile and can’t make viable offspring

imagine we took a diploid plant species and made a monoploid, an autotriploid, and an autotetraploid

order them from lowest to highest Darwinian fitness, if released in the wild

why do non-disjunction events happen?

before birth, oocytes are all formed, and arrested in meiosis I. Meiosis resumes for each oocyte just before ovulation…decades later

if a microtubule breaks/detaches during that wait, non-disjunction occurs and aneuploidy is seen in offspring

Down syndrome is caused by trisomy 21, but why don’t we hear more about monosomy 21, or other trisomies and monosomies?

most of the other aneuploids don’t survive long enough to be born

most animals have a very delicate gene balance and many recessive lethal alleles, so most aneuploids are lost before birth

chromosome 21’s small size and gene compliment is why people with trisomy 21 are more likely to survive

for which chromosome pair is aneuploidy less lethal?

iii., ii., iv., i.

deletions

when a portion of DNA is lost from the chromosome (e.g., 2 and 3)

note: the numbers indicate major chromosomal segments that each contain many genes

what can deletions be caused by?

these chromosomes are homologous

duplication

when a portion of DNA is present more than once in a chromosome

what can duplications be caused by?

these chromosomes are homologous

inversion

when a portion of DNA is turned around 180 degrees, within a chromosome

e.g., inversion of 2 and 3

what can inversion be caused by?

these chromosomes are homologous

translocation

when a portion of DNA is moved from one chromosome to another

reciprocal translation is when DNA segments are swapped, and no DNA is lost

what can translocation be caused by?

E

effects of duplications

inversions summary

acentric

has no centromere

will likely create inviable offspring

dicentric

has 2 centromeres

dicentric chromosomes will be pulled in two directions and break at a random point

will likely create inviable offspring

what happens when a crossover occurs within an inverted region