Embryology

Question 1

When do dermal ridges form on the palms and soles of the fetus?

Answer 1

Weeks 13-19

Question 2

Define induction

Answer 2

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)

Question 3

Name 4 classes of GDFs (growth and differentiation factors) that are important for cell-cell signaling during embryologic development.

Answer 3

Secreted, diffusible molecules involved in cell-cell signaling

1. Fibroblast growth factors (FGFs)
2. WNT
3. Hedgehog
4. Transforming Factor Beta (TGFB)

Question 4

Define fibroblast growth factors

Answer 4

=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

Question 5

Name the 3 hedgehog genes

Answer 5

1. Desert
2. Indian
3. 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

Question 6

Name 3 embryologic roles of FGFs.

Answer 6

Not limited to but includes:

1. angiogenesis
2. Axon growth
3. mesoderm differentiation

Question 7

Name 4 embryologic roles of SHH

Answer 7

1. limb patterning
2. neural tube induction and patterning
3. somite differentiation
4. gut regionalizations

Question 8

The receptors of the WNT proteins are in the _______ family of proteins.

Answer 8

frizzled

Question 9

Name 4 embryologic roles of WNT proteins.

Answer 9

1. regulating limb patterning
2. midbrain development
3. somite differentiation
4. urogenital differentiation

Question 10

What 3 classes of proteins are all a part of the TGF Beta superfamily?

Answer 10

1. TGFBs
2. bone morphogenic proteins
3. Mullerian inhibiting facor

Question 11

The period between two successive mitoses is called _________.

Answer 11

=interphase

• cell spends most of its life here.
• made up of G1, S, and G2 phases

Question 12

What is the stage that cells are in immediately after mitosis?

Answer 12

=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

Question 13

What are the 4 phases of the cell cycle?

Answer 13

1-3=interphases

1. G1
2. S
3. G2
4. M (mitosis)

Question 14

What happens during S phase of the cell cycle?

Answer 14

S=synthesis

-Replication of each chromosome ->form 2 sister chromatids connected by a centromere

Question 15

Name the 5 stages of mitosis

Answer 15

1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase

Question 16

What is prophase?

Answer 16

=first step in mitosis

• condensation of the chromosomes
• formation of mitotic spindle
• formation of centrosomes

Question 17

What is prometaphase?

Answer 17

=second step in mitosis

• nuclear envelope dissolves
• chromosomes attach to mitotic spindle

Question 18

What is metaphase?

Answer 18

=3rd step in mitosis

• state where chromosomes are maximally condensed
• chromosomes line up at equatorial plane of the cell

Question 19

What is anaphase?

Answer 19

=4th step in mitosis

• sister chromatids separate -> 2 independent daughter chromosomes
• daughter chromosomes move to opposite poles of the cell after they separate

Question 20

What is telophase?

Answer 20

=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

Question 21

What happens in meiosis I?

Answer 21

• 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

Question 22

What is meiotic crossing over? When does it occur?

Answer 22

=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

Question 23

True or false: the original sets of maternal and paternal chromosomes are maintained after meiosis.

Answer 23

False: the 23 pairs of homologous chromosomes assort independently into a random combination
-there are 2^23 different configurations of chromosome pairs

Question 24

When does meiotic crossing over occur?

Answer 24

Meiosis I

Question 25

How many gametes are generated at the end of meiosis I & II?

Answer 25

4 haploid gametes

Question 26

True or false: the 4 haploid gametes generated are identical to one another.

Answer 26

=False -because of meiotic crossing over (meiosis I) and random sorting of chromosomes from the original pair into daughter cells, each gamete is unique

Question 27

What cells undergo meiosis?

Answer 27

1. Primary oocytes or primary spermatocytes

Question 28

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).

Answer 28

true

Question 29

What is the difference between male and female meiosis?

Answer 29

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

Question 30

Describe the processes of meiosis that take place in an oocyte around the time of ovulation

Answer 30

- 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)