Grade 11 University Biology – Unit 2 Genetics
Mistakes in Meiosis
During Cross-over, the chemical bonds holding the DNA together are broken and reformed.
At this time, errors can occur.
Let us imagine that the illustration “MMU 11” is the
human chromosome #11. The numbers represent
segments or gene traits. RECALL: Humans have 23
pairs of chromosomes.
During Interphase, the chromatid is duplicated to
produce an identical strand (…a sister chromatid).
We now have a homogolous chromosome. During
Prophase 1 of Meiosis, a homogolous pair of
chromosomes (i.e., two homogolous chromosomes)
come together and “intertwine” around each other.
Crossover over occurs, and some mistakes occur.
Mistake 1
 Segment 7 does not bond properly. It is now
missing. Redraw the chromosome. This is called
DELETION.
Mistake 2
Segment 5 appears two additional times. In other
words, the strand has three segments of Segment 5.
As well Segment 22 appears on additional time.
Redraw the chromosome. This is called
DUPLICATION.
Mistake 3
 Sections 7, 2 and 16 are flipped and rearranged
so the order from top to bottom is 16, 2 and 7.
Redraw the chromosome. This is called
INVERSION.
Mistake 4
 A new segment of chromosome (Numbered 13) from a different chromosome is inserted
between Segment 5 and Segment 16. Redraw the chromosome. This is called
TRANSLOCATION.
Mistake 5
 The sister chromatid of MMU 11 (i.e., an identical strand) does not separate during Meiosis
phase Anaphase II. Rather, the sister chromatids stay together. Redraw the chromosome.
This is called NON-DISJUNCTION.
 The loss of a chromosome is called MONOSOMY
 The gain of an extra chromosome is TRISOMY
DO YOU UNDERSTAND? I GET IT….
 Why must the mistake describe in Mistake 5 occur in Anaphase II and not Anaphase I?
 What would happen is NON-DISJUNCTION occurred in Anaphase I?
What is the expression of the mistake?
JUST FOR FUN…and entirely wrong….
Segment Number
Trait Represented
2
Intelligence
5
Number of ears
7
Number of legs
13
Flatulency control impairment
16
Location of legs
17
Body length
22
Number of eyes
Describe or draw the change
DO YOU UNDERSTAND? I GET IT….
 Is the mistake always bad? Explain.