Developmental Genetics

Question 1

What are the homeobox characteristics?

Answer 1

• contain a highly conserved sequence of 180 nucleotides called the homeobox which codes for the 60 aa homeodomain
• play a major role in vertebrates with regard to cranio-caudal segmentation, not only along main body axis but within the development of many organs
• activated in a 3’ to 5’ direction (opposite of transcription direction)

Question 2

What are examples of homeobox containing genes?

Answer 2

• Hox
• Pax
• POU
• Lim protein genes
• Dix

Question 3

What are some mutations in homeobox containing genes?

Answer 3

• loss of function -> result in posterior to anterior transformations
• gain of function -> result in anterior to posterior transformations

Question 4

What are some groups of genes that contain the homeobox?

Answer 4

• Hox
• entrained
• paired: Pax
• POU
• LIM
• ZF (Zn finger)
• NK-2

Question 5

What direction are homeobox genes activated?

Answer 5

-3’ to 5’

Question 6

What are some characteristics of The Tbx(T-box) genes?

Answer 6

• contained a conserved T-box coding 180-200aa
• family includes up to 100 genes
• plays role in inducing mesodermal germ layer and in coordinating the outgrowth of the arm or leg

Question 7

What are some characteristics of helix-loop-helix genes?

Answer 7

• code for basic helix loop helix transcription factors
• basic regions of proteins bind to DNA
• Helix loop helix involved in homodimerization and heterodimerization
• important in myogenesis

Question 8

What are some characteristics of Forkhead(Fox) genes?

Answer 8

• type of helix loop helix family

- expressed in many developing organs throughout the body

Question 9

What are zinc finger transcription factors?

Answer 9

-the proteins have zinc ions bound to polypeptide chain that cause the chain to form finger like projections that can be inserted into the DNA helix

Question 10

What are some examples of zinc finer transcription factors?

Answer 10

• Sox genes: high mobility group domain that binds to minor groove on DNA helix rather than major groove, includes SRY gene
• WT1: important for the development of the embryonic kidney and the adult kidney. Takes name from Wilms tumor, which is a kidney tumors that develops in children

Question 11

What are the categories of developmental molecules?

Answer 11

• transcription factors
• signaling molecules
• receptor molecules

Question 12

What are the different classes of genes that control Drosophilia development?

Answer 12

-egg polarity/maternal effect genes
-segmentation genes
+Gap
+pair-rule
+segment-polarity genes
-homeotic genes

Question 13

What is the function of maternal effect genes?

Answer 13

-establish gradients from anterior and posterior poles of the egg

Question 14

What is the function of segmentation genes?

Answer 14

-define broad regions in the egg

Question 15

What are the functions of pair-rule and segment-polarity genes?

Answer 15

• define 7 segments

- define 14 segments

Question 16

What is the function of homeotic genes?

Answer 16

• determine regional characteristics

- products of homeotic genes activate other genes that encode segment specific characteristics

Question 17

What are three protein expressed in the Drosophilia ovary and how do they interact?

Answer 17

• Dorsal
• cactus
• toll
• cactus binds to the dorsal protein and traps it in the cytoplasm
• toll leads to the degradation of the cactus protein, allowing the dorsal protein to move into the nuclei of the ventral cells

Question 18

What genes in Drosophilia establish dorsal-ventral axis? Anterior-posterior?

Answer 18

Dorsal-ventral:

• dorsal
• cactus
• toll

Anterior-posterior:

• bicoid
• nanos
• hunchback

Question 19

How are egg polarity genes expressed?

Answer 19

• transcribed into mRNAs in the ovary during egg formation.
• mRNAs migrate into the eggs and are translated into proteins after fertilization
• these genes work by setting up protein gradients

Question 20

What is a morphogen?

Answer 20

-a protein that varies in concentration and causes different developmental responses as a result of the conc gradients

Question 21

What do bicoid and nanos proteins do?

Answer 21

• bicoid: responsible for anterior structures, stimulates hunchback
• nanos: responsible for posterior structures, inhibits hunchback

Question 22

Are segmentation genes maternal genes? Why/

Answer 22

NO! Because they are transcribed after fertilization

Question 23

What regulates segmentations genes?

Answer 23

-bicoid and nanos

Question 24

What are the three classes of segmentation genes and what do they do?

Answer 24

• gap genes: delete adjacent segments
• pair-rule genes: delete same part of pattern in every other segment
• segment-polarity genes: affect polarity of segment (ant. Vs post)

Question 25

How are homeotic genes activated in Drosophilia? When are they expressed?

Answer 25

• expressed AFTER fertilization
• activated by concentration of products of gap, pair-rule, and segment-polarity genes
• contain homeobox

Question 26

What are the two major groups of homeotic genes in Drosophilia?

Answer 26

• antennapedia complex: affects development of head and thorax
• bithorax complex: affects development of posterior thorax and abdominal segments