When things go wrong
in meiosis
Review of meiosis
Errors during crossing over
(Prophase I)
• Block mutations happen during meiosis and
involve the rearrangement of whole blocks of
genes.
• It can happen either spontaneously or due to
radiation.
• Block mutations include:
–
–
–
–
Deletion
Inversion
Translocation
Duplication
Block mutations
Original sequence
Mutated sequence
Deletion
ABCDEFGHMNOPQRST
ABGHMNOPQRST
Inversion
ABCDEFGHMNOPQRST
ABFEDCGHMNOPQRST
Translocation
ABCDEFGHMNOPQRST
1234567890
GHMNOPQRST
ABCDEF1234567890
Duplication
ABCDEFMNOPQ
ABCDEABCDEFMNOPQ
FMNOPQ
Errors in Independent Assortment
• Non-disjunction = failure of homologous
chromosomes to separate (Anaphase I
and Anaphase II)
Definitions
• Aneuploidy: condition that results when one cell
has a different chromosome number to the
normal chromosome number.
• Monosomy: a condition in which an individual
has only one half of a specific pair of
homologues.
• Trisomy: a condition in which an individual has
three of a specific chromosome.
• Polysomy: a condition in which an individual has
more than three of a specific chromosome.
• Haploid (n): having half of
an entire chromosome
(eg. Sex cells)
• Diploid (2n): having
double of an entire
chromosome (eg.
Somatic cells)
• Triploid (3n): having three
of an entire chromosome
• Polyploidy: a condition in
which an individual has
one or more extra of an
entire chromosome.
Polyploidy
Triploid
Tetraploid
Octaploid
Hexaploid
Faulty Gamete Production