Transcript Intro to Meiosis - Solon City Schools

Intro to Meiosis
Cell Division
• Mitosis
• Occurs in somatic
cells (body cells)
• Daughter cells
are exactly like
parent
• Diploid
• 2n
• In humans n=23
Meiosis
– Produces gametes
(germ cells/sex cells)
– Daughter cells have
half the chromosomes as parent
“Reduction division”
– Haploid
1n
Why?
• Chromatin
• Unwound, stringy
• In interphase
• Chromatids
• ½ of a replicated chromosome
• In Prophase, Metaphase
• Chromosome
• After the sisters split in
Anaphase, they are separate
chromosomes (until they unwind
into chromatin again)
Let’s look more closely at a
chromosome…
• Genes are pieces of chromosomes that
code for a protein/trait. There are
different versions (called alleles) that
create different traits (ex- hair color)
Homologues
• You have 23 pairs of chromosomes. In each pair you
received one from your mom and one from your dad.
Each pair is similar, but not exactly alike…we call them
•HOMOLOGOUS PAIRS
Note that the chromosomes
have the gene in the same
place, but different versions
of it. (one may be for
brown hair, one for blonde)
Homologous Chromosomes
• They are similar in size, shape, and the
genetic traits that they carry
Do NOT confuse these with sister chromatids
• Chromatids are exact copies
of each other made by
replication
• Homologous pairs are similar
chromosomes that are the
result of fertilization
Sister chromatids
-exact copies connected
by a centromere
Homologous Pairs
similar copies of a chromosome
One maternal, one paternal
1m
1m
1p
1m
1p
or
1p
Boy Karyotype- displays
homologous pairs
Female Karyotype
Replicated chromosomes after “S”
phase of interphase
Haploid vs. Diploid
• DIPLOID CELLS: have two
versions of each chromosome
(one from mom AND one from
dad)
•
•
•
•
•
Has the homologous pairs
Somatic cells (body cells)
Made by mitosis or fertilization
“2n”
In this picture, what is “n”?
• n=2
Diploid vs. Haploid
• Haploid cells: Have
only ONE copy of
each chromosome.
• NO HOMOLOGOUS
PAIRS present
• Gametes (sex cells:
egg and sperm)
• Made by MEIOSIS
• “1n”
Mitosis- divides somatic cells to
get tissues and organs built;
makes individual grow into an
adult