Gametogenesis= the formation of
gametes
involves
Spermatogenesis in male
and oogenesis in female
Spermatogenesis: formation of
sperms
• Cytoplasm is divided equally during each division, forming 4
equal sized sperms
• Sperms are small in size and streamlined for maximum
motility
• Male adult can produce 200 millions sperms/day
Oogenesis: Formation of egg cells (or
ova)
•Of 4 daughter cells formed, one receives the most cytoplasm.
The other three cells called polar bodies die
•The final product of oogenesis is therefore a single ovum or egg
cell.
•All egg cells stop developing at the end of prophase I after a
female mammal is born.
•A female human produces 400-500 eggs during her lifetime
Sex determination
Sex influenced by chemical pollutants
• Atrazine- a herbicide
• Proposed as the cause for the feminization of
male frogs
Dr. Tyrone Hayes- UC Berkeley
We’re all the same up until the 7th
week of development
In human embryos, the SRY gene activates a testisforming pathway at about week seven of development.
Errors in Meiosis
1. Errors caused by changes in
chromosome number
(i.e. non-disjunction)
2. Errors caused by changes in
chromosome structure
(i.e. mutation)
Predict disorder interactive quiz
http://learn.genetics.utah.edu/content/begin
/traits/predictdisorder/
1. Non-disjunction: the failure of homologous pairs or
sister chromatids to separate during meiosis
What are some implications of nondisjunctions?
• One daughter cell will have an extra
chromosome while the other will be
missing a chromosome
• Cells with extra chromosomes or missing
a chromosome are not able to function
normally
Down syndrome
Karyotype shows 3 copies
of chromosomes 21
• Edward
• Patau
syndrome
Errors in Meiosis
1. Errors caused by changes in
chromosome number
(i.e. non-disjunction)
2. Errors caused by changes in
chromosome structure
(i.e. mutation)
The Secrets of the Sequence: On Down – Down Syndrome Video
https://www.youtube.com/watch?v=bEVkbuooXo4
1. What is the typical number of chromosomes in a child who has Down Syndrome?
47
2. What were the key developments that made it possible for researchers to get a better
understanding of Down Syndrome?
- Mapping of human genome
- Ability to grow stem cells in a dish
3. What are some common features of Down Syndrome mentioned in the video?
People with Down Syndrome have similar facial features (broad faces and upward
slanted eyes).
They will also have some form of mental impairment.
They will develop a form of Alzeheimer’s Disease during their life.
They have an accelerated aging process.
They have an extra copy of chromosome 21.
4. Why is stem cell research so important to the study of Down Syndrome?
Initially Down Syndrome studies were performed on mice, but mice do not even have
Chromosome 21. The ability to grow stem cells from Down Syndrome fetal tissue and
compare them to stem cells from non-Down Syndrome patients makes it possible to
determine if replication of these cells occur in the same way. For example, it is now
possible to view the development of stem cells into neuron cells, and it is clear that there
are significant reduction in rates of neuron development in the Down Syndrome
(DS) compared to non-DS stem cells.
Turner Syndrome – NJN News Healthwatch Report
http://www.youtube.com/watch?v=ldjb-FR-PKo
1. What are the general symptoms of Turner’s Syndrome?
45 chromosomes (missing one X)
short stature, puffy hands, shortened 4th and 5th toes, webbed neck, low set ears,
breast underdevelopment, infertile
2. What is used to treat Turner’s Syndrome (TS)?
Estrogen- female hornome
3. What would would be the genotype (genetic make-up) of someone who has TS?
______________
XO
4. Why is detection of Turner’s Syndrome so important?
To repair congenital heart defects commonly seen with TS patients
Also, to administer hormone in time of puberty
It helps reducing emotional/psychological burden on person with TS
Homework
• Practice meiosis with provided handout
• Review similarities/differences b/t mitosis
and meiosis
• Look at different types of mutation
• Predict disorder interactive quiz:
• http://learn.genetics.utah.edu/content/begi
n/traits/predictdisorder/