Cell Differentiation
and
Meiosis
Study guide
•
Compare the processes and products of meiosis I and meiosis II.
•
Compare the overall processes and products of meiosis and mitosis.
•
Explain how independent assortment of chromosomes during meiosis, and crossing over
contribute to genetic diversity in offspring.
•
Explain what makes the many types of adult human cells different.
•
Explain how every cell has the potential to act like every other cell.
•
Compare the properties of embryonic and adult stem cells. Explain the advantages and
disadvantages of using adult stem cells to produce replacement tissues.
Human Life Cycle:
mitosis for development and meiosis for reproduction
1
A pancreas cell, eye cell and nerve cell in your body:
Are these cells duplicates of the original cell (zygote)?
Are these cells genetically identically to each other
(same number and type of chromosomes) ?
Does a eye cell have the gene to make insulin?
Why are they different in form and function?
Most cells in an adult body are differentiated
Differentiated cells are specialized in form and function
Differentiated cells have a particular
pattern of genes that are expressed
and not expressed
How do cells become differentiated?
2
Cell differentiation occurs during
the embryo development
Early cells are not differentiated
(Stem Cells)
during development
cells become more specialized
(differentiated)
by getting some genes activated
and some others inactivated
NOTE:
Not all stem cells have the same
level of “stemness”
Stem cells are found in the embryo and adult but
vary in their stemness
3
Why is studying stem cells useful?
Stem Cell Therapy:
embryonic stem cells vs. adults stem cells
How those their potential as therapy
vary?
What are the ethical considerations?
Special considerations of both?
4
Embryonic stem ce3lls through therapeutic cloning
In 2013, for the first time, a
group of researchers used
therapeutic cloning to make ES
cells.
The donor nucleus came from
a child with a rare genetic
disorder.
However, the cloning process
remains time consuming,
inefficient, and expensive.
iPS cells: Induced Pluripotent Stem cells
iPS cells are much less
expensive to create than ES
cells generated through
therapeutic cloning
However, because the
"reprogramming" process
introduces genetic
modifications, the safety of
using iPS cells in patients is
uncertain.
5
Human Life Cycle:
mitosis for development and meiosis for reproduction
Our somatic cells have a total of
____ chromosomes in each cell
These cells have two chromosomes of each type
6
Two chromosomes that carry the same genes are
called homologous chromosomes
In a homologous pair :
One of the chromosomes was inherited from father
One of the chromosomes was inherited from mother
In a homologous pair:
both chromosomes have the same genes,
but are not necessarily identical
(they might be different versions,
different sequence of bases)
Pretend Cell
How many chromosomes does
this cell have?
How many types of chromosomes
does this cell have?
(note size of chromosomes)
Does this cell have homologous
pairs of chromosomes?
How many pairs?
Has this cell been through the S
phase?
7
Diploid cells and Haploid cells
Diploid cell: symbol (2n)
has two sets of chromosomes
has PAIRS of HOMOLOGOUS chromosomes
all somatic cells are diploid
HAPLOID cells: symbol (n)
has one set of chromosomes
has only one of each kind
Gametes are haploid
Is this cell haploid or diploid?
8
What about this cell?
Chromosome
Homologous pair of
chromosomes
Gametes are produced
by a different type of cell division called meiosis
• # of cells produced
•
# of chromosomes in daughter cells vs. parent cell
One (diploid) mother cell  4 (haploid) daughter cells
9
Table comparing the stages of meiosis
STAGES OF
MEIOSIS
HOW ARE THE
CHROMOSOMES
ARRANGED DURING
METAPHASE?
WHAT SEPARATES
DURING ANAPHASE?
ARE CELLs HAPLOID
OR DIPLOID ATH THE
END OF THIS STAGE?
Meiosis I
Meiosis II
Meiosis 1: homologous chromosomes separate
Prophase 1: homologous chromosomes pair up (crossing over can occur)
Metaphase 1: homologous pairs line up in the middle (randomly)
note: double file
Anaphase 1: homologous chromosomes separate
Result of meiosis 1:
two haploid cells, each chromosome has two chromatids
10
Meiosis II: sister chromatids separate
Metaphase 2: chromosomes line up in the middle
Anaphase 2: Chromatids separate (note: single file)
Result of Meiosis II: four haploid daughter cells
Accidents during meiosis can alter
chromosome number in gametes
Cause: Non disjunction
the chromosomes in a pair of chromosomes
or sister chromatids fail to move apart properly
Result: gametes have an extra or a one less chromosome
11
An extra copy of chromosome 21
causes Down Syndrome
12
Mitosis vs Meiosis
Mitosis
Meiosis
Number of DNA replication events
Number of cytokinesis events
Number of daughter cell produced
Number of sets of chromosomes in daughter cells
Genetic relationship of daughter cells to the
parent cell (identical or non identical)
Purpose in human body
13