Colchicine is a naturally occurring alkaloid in the autumn crocus that interferes with spindle formation Autopolyploidy

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

Paracentric inversion heterozygote (centromere not included) not viable dicentric bridge Note that crossover events not observed

Pericentric inversion heterozygote (centromere included) not viable Note that crossover events not observed

Translocations - usually, but not always, observed between different chromosomes ABCDEFG Nonreciprocal Translocation HIJKLM ABCDE HIJKLMFG

Translocations - usually, but not always, observed between different chromosomes ABCDEFG Reciprocal Translocation HIJKLM ABCDE HIJKFG LM

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

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

Robertsonian Fusion is most common type of translocation observed in humans (1 in 1000 live births) break at centromere of two acrocentric chromosomes fusion of broken chromosomes

Robertsonian Fusion in one parent between chromosomes 14 and 21 is responsible for a heritable form of Down Syndrome (<5% of cases) normal, despite 2N=45

A male Drosophila from a wild type stock was discovered to have 7 chromosomes, whereas the normal 2N number is 8. A karyotype revealed that a nonreciprocal translocation had occurred so that one copy of chromosome 4 had attached to the end of chromosome 2. It lost its centromere. Diagram all members of chromosomes II and IV during synapsis in Meiosis I

A male Drosophila from a wild type stock was discovered to have 7 chromosomes, whereas the normal 2N number is 8. A karyotype revealed that a nonreciprocal translocation had occurred so that one copy of chromosome 4 had attached to the end of chromosome 2. It lost its centromere. Diagram all members of chromosomes II 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 the recessive chromosome IV mutation eyeless (ey), what chromosome compositions will occur in the offspring regarding chromosomes II and IV? What phenotypic ratio will result regarding the presence of eyes, assuming all abnormal chromosome compositions survive? 1) normal (heterozygous) 2) eyeless (monosomic) 3) normal (heterozygous) 4) normal (heterozygous with translocated copy of chromosome 4) IV II

Pretend you are a genetic counselor. A woman was found to be heterozygous for a chromosomal rearrangement between the second and third chromosomes. What type of chromosomal aberration is this?

How would these chromosomes pair during synapsis? A BC D E FC D A B G H G H E F

This woman is phenotypically normal. Why? Under what circumstances might a phenotypic effect occur? -breaks within genes -if there are “position effects”