Colchicine is a naturally occurring alkaloid in the autumncrocus that interferes with spindle formation

Autopolyploidy

Homologous pairing of chromosomes in individuals that areheterozygous for an inversion is achieved via an inversion loop

Paracentric inversion heterozygote (centromere not included)

not viable

not viable

dicentric bridge

Note that crossover events not observed

Pericentric inversion heterozygote (centromere included)

not viable

not viable

Note that crossover events not observed

Translocations

- usually, but not always, observed between different chromosomes

A B C D E F GNonreciprocal Translocation

H I J K L M

A B C D E

H I J K L M F G

Translocations

- usually, but not always, observed between different chromosomes

A B C D E F GReciprocal Translocation

H I J K L M

A B C D E

H I J K F G

L M

Homologous chromosomes that are heterozygous for a translocation form a crosslike configuration during synapsis

Segregation of chromsomes during meiosis produces somegametes that are unbalanced (i. e. genes are missing).These gametes cause infertility or lethality (if fertilization occurs).

Robertsonian Fusion is most common type of translocationobserved in humans (1 in 1000 live births)

break at centromere of twoacrocentric chromosomes

fusion of broken chromosomes

Robertsonian Fusion in one parent between chromosomes 14 and 21 isresponsible for a heritable form of Down Syndrome (<5% of cases)

normal, despite2N=45

A male Drosophila from a wild type stock was discovered to have7 chromosomes, whereas the normal 2N number is 8. A karyotyperevealed that a nonreciprocal translocation had occurred so that onecopy of chromosome 4 had attached to the end of chromosome 2. Itlost its centromere.

Diagram all members of chromosomesII and IV during synapsis in Meiosis I

A male Drosophila from a wild type stock was discovered to have7 chromosomes, whereas the normal 2N number is 8. A karyotyperevealed that a nonreciprocal translocation had occurred so that onecopy of chromosome 4 had attached to the end of chromosome 2. Itlost its centromere.

Diagram all members of chromosomesII and IV during synapsis in Meiosis I

-chromosomes replicated-two pairs of sister chromatids for II-one pair of sister chromatids for IV

If this male mates with a normal female who is homozygous for therecessive chromosome IV mutation eyeless (ey), what chromosomecompositions will occur in the offspring regarding chromosomes IIand IV?

What phenotypic ratio will resultregarding the presence of eyes,assuming all abnormal chromosomecompositions survive?

1) normal (heterozygous)2) eyeless (monosomic)3) normal (heterozygous)4) normal (heterozygous withtranslocated copy of chromosome 4)

IVII

Pretend you are a genetic counselor. A woman was found to beheterozygous for a chromosomal rearrangement between thesecond and third chromosomes.

What type of chromosomal aberration is this?

How would these chromosomes pair during synapsis?

A B C

D

EFC

D

A B G

H

G

H

EF

This woman is phenotypically normal. Why? Underwhat circumstances might a phenotypic effect occur?

-breaks within genes-if there are “positioneffects”