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Alex's Genetics > Lecture 21a > Flashcards

Lecture 21a Flashcards

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Biology 101 flashcards
1
Q

At first, it appeared that Drosophila approached development very differently. However, what is now known from mutant screens?

A

The genes in Drosophila are homologs to mammalian development and related development.

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2
Q

What do the homologs between Drosophila and other species show?

A

Structures can appear to develop very differently yet use very similar genes.

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3
Q

What is the first stage in Drosophila embryonic development?

A

The establishment of the body axes.

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4
Q

How do the body axes become established in Drosophila during embryonic development?

A

The establishment of the body axes starts during oogenesis in which certain gene products (morphogens) important in early development are deposited asymmetrically within the egg.

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5
Q

T/F: Morphogens are deposited symmetrically within the egg.

A

False! Morphogens are actually deposited asymmetrically in the head.

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6
Q

With the asymmetric deposition of Morphogens in the Drosophila embryo, what does this establish?

A

The Morphogens establish the axes of polarity in the Drosophila embryo.

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7
Q

Where is the Bicoid mRNA concentrated?

A

Bicoid mRNA is concentrated in the area that will become the head.

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8
Q

Where is the Nanos mRNA concentrated?

A

Nanos mRNA is concentrated in the area that will become the tail/rear.

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9
Q

What happened when people mutated the Bicoid gene?

A

The embryo partially lost its head-tail orientation and now developed with 2 posterior ends (spiracles).

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10
Q

T/F: Bicoid mRNA is distributed anteriorly and the Nanos mRNA is distributed posteriorly.

A

True!

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11
Q

If a larva was defective in the Bicoid gene, how will it develop?

A

Develops with 2 posterior ends (spiracles).

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12
Q

Where is the Bicoid gene actively transcribed? After it is transcribed, where does it move to?

A

Actively transcribed in the nurse cells, which is outside of the oocyte.

Then, it diffuses across into the oocyte.

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13
Q

Where does Bicoid mRNA enter the oocyte?

A

Enters the anterior end of the oocyte and is trapped there.

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14
Q

What are 2 techniques we can use to see where gene products reside in the embryo?

A

1) In situ hybridization of Bicoid mRNA
2) Immunostaining of Bicoid protein (similar to Western Blot but on an embryo)

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15
Q

What is In situ hybridization of Bicoid mRNA?

A

It is essentially RNA FISH on an embryo. The DNA is not denatured so the probe only recognizes RNA, allowing us to visualize gene products (because thats what RNA is).

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16
Q

What is involved in Immunostaining of the Bicoid protein?

A

The embryo is exposed to primary antibodies recognizing Bicoid protein and then to secondary antibodies that recognize the primary antibodies and are also linked to a fluorescent molecule.

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17
Q

During Drosophila development, the oocyte first starts as one cell, then it becomes a Syncytial blastoderm. What does it mean?

A

The oocyte gets fertilized, then the nucleus divides, but NOT the actual cell. Cells will form around each nucleus.

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18
Q

What are Syncytial blastoderm nuclei?

A

A ring of nuclei that form within a cell.

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19
Q

In Drosophila development, the zygote goes through a series of _________ divisions, but NOT __________ divisions.

A

nuclear, cytoplasmic

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20
Q

Eventually, the Syncytial blastoderm will form what? What else clusters and forms?

A

Forms Blastoderm cells.

Germ cells will also cluster on the outer edges of the posterior end.

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21
Q

After Blastoderm cells are formed, what does the embryo undergo? What is this?

A

Undergoes Gastrulation, which is when the cell goes from a single cell layer to three cell layers.

22
Q

Name the 3 cell layers formed in Gastrulation.

A

Ectoderm (outside), Mesoderm (middle), and endoderm (inside).

23
Q

What is Gastrulation?

A

Blastoderm cells undergo a series of complicated cell movements that turn single-cell layer into 3 cell layers from invaginating cells.

24
Q

Gastrulation involves a great deal of cell migration. What does this form?

A

Forms the embryo

25
Q

What occurs after Gastrulation?

A

Segmentation

26
Q

What is Segmentation?

A

Segmentation genes get expressed in specific regions of the embryo, causing the embryo to become segmented.

27
Q

From anterior to posterior, the segments have been given _____.

A

names

28
Q

T/F: The anterior and posterior halves of each segment are the same in terms of genes and gene expression.

A

False! The anterior half of each segment in the Drosophila embryo is different from the posterior half in terms of genes and gene expression.

29
Q

In addition to segments, what else can the embryo be divided into? What are these?

A

Can also be divided into parasegments, which is when we have the anterior half of one segment with the posterior half of another segment.

30
Q

The segments and parasegments are out of __________. This means that the anterior part of a segment coincides with the posterior region of a parasegment that came before it.

A

register

31
Q

Scientists found genes that when mutated, screw up segmentation. Name the 3 types of segmentation genes.

A

1) Gap genes
2) Pair-rule genes
3) Segment-polarity genes

32
Q

What are Gap Genes?

A

Genes in which a group of continuous segments are missing, resulting in a shorter embryo.

33
Q

What are Pair-Rule Genes?

A

Genes in which every other segment/parasegment is missing from the larvae. The missing segments can be even or odd-paired segments missing.

34
Q

What are Segment-Polarity genes?

A

Normally, these establish polarity within genes. However, mutations in these produce a segment that is more uniform, meaning there is less of an anterior and posterior part to each segment.

35
Q

What is Metamorphosis?

A

The transition from segmented larva to the adult fly body plan.

36
Q

In metazoa, what is the final result in development?

A

An adult body organized along 3 axes.

37
Q

In the final stages of development, what does the Drosophila get wrapped up in?

A

A pupal case

38
Q

During metamorphosis, what do the 19 imaginal discs in the larvae do?

A

They develop into adult structures.

39
Q

Scientists discovered other genes that were found to be really important in development called Homeotic Genes. What do these determine?

A

Homeotic Genes determine the segment identity / phenotype.

40
Q

Define the term Homeotic.

A

Refers to mutant alleles in which one body part is replaced by another.

Basically, if you have a mutant allele, it can make that segment resemble another segment.

41
Q

What does Cell Fate mean?

A

Describes the ultimate morphological features of a cell or group of cells.

Each segment has a different fate.

42
Q

T/F: In Drosophila, the cells in each body segment have their fate determined very early in embryological development, long before morphological features become apparent.

A

True!

43
Q

How is the expression pattern of homeotic genes in Drosophila shown?

A

They are in 2 clusters that are physically separated from each other. Antennapedia complex and bithorax complex.

44
Q

The order of gene expression anterior to posterior ____________ the order of genes on the chromosome. Each of these genes encodes for a ___________ ___________.

A

parallels, transcription factor

45
Q

What determines the color of a segment in Drosophila homeotic genes?

A

The most posterior-expressed homeotic gene determines the color of the segment.

46
Q

What is the expression pattern of homeotic genes determined by?

A

By 2 groups of chromatin-promoting proteins, Polycomb genes and Trithorax genes.

47
Q

What do Polycomb genes do?

A

Encode heterochromatin which will repress the expression of homeotic genes in regions of the embryo where they should NOT act.

48
Q

What do Trithorax genes do?

A

Encode euchromatin which will promote the expression of homeotic genes in regions of the embryo where they should act.

49
Q

Polycomb heterochromatin limits ____ gene expression to specific sets of segments. As we go to the ___________ end of the fly, more and more homeotic genes are being expressed.

A

Hox, posterior

50
Q

What is the homeotic gene that is being expressed in a segment?

A

The homeotic gene that is closest to the heterochromatin-euchromatin boundary is the one that is being expressed in a segment.

Alex's Genetics (38 decks)

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