Meiosis And Gametogenesis Flashcards
Somatic cells vs germline cells
Does germline undergo meiosis or mitosis?
Germline= sperm and egg; somatic= everything else
Germline undergoes mitosis until gametogenesis then it undergoes meiosis
What is the result of meiosis I?
Two haploid cells formed but chromosomes are still double
Meiosis I: Prophase I
- What is significant about synaptonemal complex?
- What is the site of cross over?
- Explain kinetochores
- Region of close association where crossing over occurs
- Chiasmata
- Kinetochores are located on centromeres and attach homologous chromosomes to spindle fibers from opposite poles
Meiosis I: Metaphase I
What is happening here?
Tetrads line up along the midplane of the cell
Meiosis I: Anaphase I
What happens?
Homologous chromosomes separate and move toward opposite poles (each pole gets one set of homologous chromosomes)
Meiosis I: Telophase I
What happens
Spindle disintegrates, cytokinesis (divison) occurs
Period between meiosis I and II is called?
Interkinesis
Meiosis two is basically the same as meiosis one except?
Phases are shorter
How are nuclei formed during telophase II
Nuclear membranes reform around the genetic material to form nuclei
Differences between meiosis and mitosis
MITOSIS: one division, results in 2 genetically identical daughter cells, do not pair, cross over, or segregate
MEIOSIS: two divisions, results in 4 genetically distinct daughter cells, pair (synapsis), cross over (homologous recombination), and segregate
Spermatogenesis typically produces __ haploid sperms for each germ cell
oogenesis typically produces __ haploid eggs for each germ cell
Where does the rest of the genetic material go?
4
1 (ovum)
Polar bodies: eventually die (cannot be fertilized)
Gametogenesis:
- Primordial germ cells are formed ___ during the __ week and move to ___
- During __ week, they move to __
- Germ cells undergo gametogenesis in preparation for?
- Meiosis is for?
- Cytodifferentiation is for?
- In the epiblast during the second week and move to the yolk sac
- 4th week to developing gonads (get there by week 5)
- Fertilization
- Reduce chromosome number
- Complete maturation (oocytes vs spermatozoa)
Spermatogenesis:
- At birth what is present in the sex cords of the testis?
- What do supporting cells develop into?
- What do sex cords become after puberty?
- What do primordial germ cells give rise to?
- Primordial germ cells and supporting cells
- Sustentacular (sertoli) cells
- Sex cords acquire a lumen and become the seminiferous tubules
- Spermatogonial stem cells
- What marks the beginning of spermatogenesis?
- Last division of the answer to number 1 produces?
- These divide to form?
- Cells emerging from spermatogonial cell population to form type A spermatogonia
- Type B spermatogonia
- Primary spermatocytes
Primary spermatocytes undergo meiosis I to produce ____ ….
Secondary spermatocytes which undergo meiosis II to produce spermatids
Difference between spermatogenesis and spermiogenesis?
Spermiogenesis transforms __ to __
Spermatogenesis = formation of sperm cells Spermiogenesis= maturation of spermatids into sperm cells (so final differentiation and maturation)
Transforms spermatids to spermatozoa
Phases of spermiogenesis and what is happening: (3)
- Golgi phase= golgi membrane forms cap over nucleus (preparing to acquire head, mid-piece, and tail
- Acrosome phase= formation of acrosome (head) from golgi
- Tail phase= formation of flagellum, microtubules form contractile axoneme, mitochondria is organized in middle and head
Spermatogonia vs spermatids?
Where are they located throughout their development?
What hormone regulates spermatogenesis?
Spermatogonia are the stem cells; spermatids are the products of second meiotic division
Sertoli cells (which protect and support germ cells)
LH
Brief summary of spermatogenesis
Type A -> type B -> primary spermatocytes -> secondary spermatocytes -> spermatids -> spermatozoa (sex cells that carry genetic information)
Oogenesis:
- Primordial germ cells differentiate into?
- Oogonia go through mitosis, but what happens by the 7th month?
- Then what?
- Oogonia
- Most oogonia are lost, remaining ones enter meiosis I and become primary oocytes
- Primary oocytes become surrounded by epithelial cells; primary oocytes remain arrested in prophase I and do not complete meiosis I until after puberty
Explain follicular growth and maturation at the time of puberty
At puberty each month, primordial follicles begin to grow, the growing follicles are now called primary follicles and surrounding epithelial cells become cuboidal and proliferate to granulosa cells
Primary follicles:
Granulose cells and oocyte secrete glycoprotein layer around oocyte called?
Zona pellucida (has cytoplasmic projections to transport materials from granulosa cell to oocyte)
Where is the oocyte found - explain this space
The edge of the antrum (surrounded by granulosa cells). The antrum is formed from fluid filled spaces that develop between granulosa cells as follicle grows
(Antrum becomes huge)
- How many follicles reach maturity each ovarian cycle?
- Oocyte of mature follicle completes meiosis I due to ?
- Result of meiosis I?
- One
- Surge of LH
- Secondary oocyte and first polar body
After meiosis I, secondary oocyte enters meiosis II. Stays in metaphase there until?
When will meiosis II complete?
3 hours before ovulation
Only if the oocyte is fertilized
What could lead to an extra or missing chromosome (aneuploidy)?
What is aneuploidy?
What is euploidy?
Nondisjunction of chromosomes during cell division
Aneuploidy= abnormal number of chromosomes (45 or 47 instead of 46)
Euploidy= an entire set of chromosomes is duplicated once or several times
- Klinefelter syndrome results in ? And is caused from?
2. Turner syndrome results in? Usually caused from?
- XXY; usually nondisjunction of the XX homologues
2. XXX; nondisjunction in the male gamete
- What is a translocation?
2. Deletions vs microdeletions
- Chromosome breaks and a portion of it reattaches to a different chromosome
- Microdeletions- too small to be detected by karyotype
Trisomy 21 usually occurs from?
Down syndrome occurs from?
Angelman syndrome?
Prader-Willi syndrome?
Nondisjunction in oocyte (increased risk with maternal age)
Karyotype of translocation of chromosome 21 onto 14
Deletion of maternal contribution on chromosome 15
Deletion of paternal copies of SNRPN and NDN (imprinting) located on chromosome 15
