Embryology Flashcards
When do dermal ridges form on the palms and soles of the fetus?
Weeks 13-19
Define induction
The process whereby one group of cells or tissues causes another set of cells or tissues to change their fate.
- Important for embryologic formation of organs
- Happens mostly through cell-cell signaling through either secreted molecules (paracrine) or direct cell-cell interactions (juxtacrine)
Name 4 classes of GDFs (growth and differentiation factors) that are important for cell-cell signaling during embryologic development.
Secreted, diffusible molecules involved in cell-cell signaling
- Fibroblast growth factors (FGFs)
- WNT
- Hedgehog
- Transforming Factor Beta (TGFB)
Define fibroblast growth factors
=family of proteins that are involved in cell-cell signaling during development
- secreted proteins that bind to fibroblast growth factor receptors on various cells to activate various pathways
- 25 genes with hundreds of different isoform FGF proteins generated by alternative RNA splicing
- Can act on different pathways for different specific developmental events
Name the 3 hedgehog genes
- Desert
- Indian
- Sonic hedgehog (SHH)
These are secreted proteins that are involved in cell-cell signaling. SHH binds to a receptor called Patched which binds to a protein (smoothened or SMO). Once SHH binds, inhibition on SMO released and SHH signal transduced
Name 3 embryologic roles of FGFs.
Not limited to but includes:
- angiogenesis
- Axon growth
- mesoderm differentiation
Name 4 embryologic roles of SHH
- limb patterning
- neural tube induction and patterning
- somite differentiation
- gut regionalizations
The receptors of the WNT proteins are in the _______ family of proteins.
frizzled
Name 4 embryologic roles of WNT proteins.
- regulating limb patterning
- midbrain development
- somite differentiation
- urogenital differentiation
What 3 classes of proteins are all a part of the TGF Beta superfamily?
- TGFBs
- bone morphogenic proteins
- Mullerian inhibiting facor
The period between two successive mitoses is called _________.
=interphase
- cell spends most of its life here.
- made up of G1, S, and G2 phases
What is the stage that cells are in immediately after mitosis?
=G1
- 1 diploid copy of the genome
- no DNA synthesis
- Amount of time a cell spends in this part of the cycle varies by the type of cell and whether or not there is damage to the cell
What are the 4 phases of the cell cycle?
1-3=interphases
- G1
- S
- G2
- M (mitosis)
What happens during S phase of the cell cycle?
S=synthesis
-Replication of each chromosome ->form 2 sister chromatids connected by a centromere
Name the 5 stages of mitosis
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is prophase?
=first step in mitosis
- condensation of the chromosomes
- formation of mitotic spindle
- formation of centrosomes
What is prometaphase?
=second step in mitosis
- nuclear envelope dissolves
- chromosomes attach to mitotic spindle
What is metaphase?
=3rd step in mitosis
- state where chromosomes are maximally condensed
- chromosomes line up at equatorial plane of the cell
What is anaphase?
=4th step in mitosis
- sister chromatids separate -> 2 independent daughter chromosomes
- daughter chromosomes move to opposite poles of the cell after they separate
What is telophase?
=5th and final step in mitosis
- 2 separate sets of daughter chromosomes, one at each pole of the cell
- chromosomes decondense
- nuclear membrane reforms
- cleavage of the cytoplasm into 2 daughter cells
What happens in meiosis I?
- number of chromosomes in each daughter cell is reduced by half because the homologous chromosomes are split up and one homologue in each pair goes into a different daughter cell
- genetic recombination also occur
What is meiotic crossing over? When does it occur?
=homologous segments of DNA are swapped between the chromosome pair
- ensures that none of the gametes will be identical to one another
- occurs during Meiosis I
True or false: the original sets of maternal and paternal chromosomes are maintained after meiosis.
False: the 23 pairs of homologous chromosomes assort independently into a random combination
-there are 2^23 different configurations of chromosome pairs
When does meiotic crossing over occur?
Meiosis I
How many gametes are generated at the end of meiosis I & II?
4 haploid gametes
True or false: the 4 haploid gametes generated are identical to one another.
=False
-because of meiotic crossing over (meiosis I) and random sorting of chromosomes from the original pair into daughter cells, each gamete is unique
What cells undergo meiosis?
- Primary oocytes or primary spermatocytes
True or false: male and female gametes have different patterns of gene expression, marked by their developmental origins (either from an XY or XX embryo).
true
What is the difference between male and female meiosis?
In females meiosis is initiated once, during early fetal life, in a limited number of primary oocytes
In males, meiosis is initiated continuously in many cells from a dividing populations throughout the adult life of a male
Describe the processes of meiosis that take place in an oocyte around the time of ovulation
- primary oocytes are generated from oogonia (primordial germ cells) beginning in the 3rd month of fetal life
- primary oocytes are suspended in prophase I of meiosis I until sexual maturity
- At the time of ovulation, the oocyte completes meiosis 1. One of the 2 daughter cells becomes the secondary oocyte (egg), the other becomes the first polar body
- Meiosis II starts and proceeds to metaphase during ovulation, arrests and meiosis II only completes if fertilization occurs (and generates a second polar body)
