Meiosis
Vocabulary
• Karyotype = a diagram of the
chromosomes (arranged in order for
study)
Vocabulary
• Somatic cells = body cells (ex. Leg, nose,
kidney etc. cells)
• Germ cells = sex cells (egg or sperm)
• Homologous = containing the same kind
of genetic information
• Gamete = sex cells (egg or sperm)
Vocabulary
• Haploid cell (n) = having one of each type
of chromosomes
• *** Sex cells are haploid. In humans, that
number is 23.
Vocabulary
• Diploid cell (2n) = having a pair of each
type of chromosome
*** Somatic cells are diploid. In humans, the
diploid number is ________.
Vocabulary
• Autosomes = the non-sex chromosomes;
found in all cells
*** In humans, chromosomes 1-22 are
autosomes
Vocabulary
• Sex chromosomes = the chromosomes
that determine gender; found in all cells.
*** In humans, the sex chromosomes are in
the 23rd position on the karyotype
Meiosis
• process in which the chromosome # is
reduced from diploid to haploid. Also
called “reduction division”
Q: Is meiosis sexual reproduction or asexual
reproduction?
Q: What process have we learned about that
is considered asexual reproduction?
Meiosis facts
• produces sex cells
• occurs in ovaries and testes in animals
• occurs in the ovaries and anthers in plants
Fertilization
• When fertilization occurs, 2 gametes are
united to form a zygote. Zygotes are
diploid.
Prophase I
• Crossing over-the swapping of DNA
(chromosome leg) for homologous
chromosomes.
Draw crossing over
Before Crossing Over
After Crossing Over
Why is crossing over important?
• Crossing Over leads to genetic variation.
Homologous chromosomes
• Contain the same genetic information!
Meiosis
• During Meiosis
chromosomes are
randomly separated
and paired into the
sex cells created.
This is known as
Random Assortment
of Chromosomes.
Thus your sex cells
pass on DNA from
both your mother and
father.
Meiosis I
Meiosis II
Meiosis mistakes
• Nondisjunction= the chromosomes do
not separate properly
3 types of Nondisjunction
1. trisomy = (2n +1) one extra chromosome
in zygote (Ex . Down’s syndrome is a
trisomy 21)
3 types of nondisjunction
2. monosomy= (2n -1) one missing chromosome;
usually lethal in humans except if it is in sex
chromosomes (Ex. Turner’s syndrome)
Turner’s syndrome
3 types of nondisjunction
3. triploid = (3n) total lack of separation of all
homologous chromosomes