Deck 20: Developmental Genetics

Question 1

Maternal effects are cases of extrachromosomal inheritance in which the genotype of the mother influences the phenotype of her immediate offspring in a non -Mendelian manner. Provide a rationale for the molecular basis of a maternal effect.

Answer 1

During development of the egg, females provide numerous nutritional and informational substances, which direct and support early embryonic
development. These substances are often in the form of transcription factors, receptors, mRNA, and proteins, although other substances are also likely
(substrates and products). In some cases, these maternally supplied substances override the actual genotype of the zygote and produce a phenotype much like the genotype of the mother.

Question 2

Mutations that eliminate a contiguous region in the Drosophila embryo's segmentation pattern are called _.

A) homeodomains
B) compartment genes
C) linkage genes
D) gap genes
E) segment genes

Answer 2

D

Question 3

Provide a brief description of the variable gene activity hypothesis as it relates to development. What information is often provided in support of this hypothesis?

Answer 3

Because all cells apparently have the same genetic information, yet may differ
structurally and functionally, the variable gene activity hypothesis suggests that differential gene transcription (genetic regulation) accounts for such cellular
diversity. Evidence in support of this model includes the following:
chromosome puffs, isozymes, and the presence of genes but no gene products in some tissues (hemoglobin, for example).

Question 4

Distinguish between segmentation genes and homeotic genes. 20)

Question 5

Which of the following is a fundamental characteristic of the Notch pathway?

A) It directs mRNAs to antisense systems in the posterior portion of all organisms.
B) It works through direct cell -to -cell contact.
C) It provides symmetry to plant flowers.
D) It works through nuclear signals involving the lac operon.
E) It allows mRNAs to accumulate in the posterior portion of the Drosophila embryo.

Question 6

Immediately after fertilization of a Drosophila egg, the zygote nucleus undergoes a series of divisions. Subsequent nuclear migration generates a(n) _.

A) homeodomain
B) maternal effect
C) zygote
D) syncytial blastoderm
E) endoderm

Question 7

Provide a brief description of segment polarity genes, including their regulation and their molecular and developmental effects.

Question 8

Experiments involving nuclear transplantation in amphibians indicate that nuclei
derived from blastula are more likely to support development of complete and normal adults compared with those derived from later stages of development. What do these experiments tell us about the process of development?

Question 9

Which function earlier in development: maternal -effect genes or zygotic genes? 17)

Question 10

How does determination relate temporally to differentiation?

Question 11

In Drosophila, what is the order of function of the segmentation genes? 18)

Question 12

What kinds of general observations cause one to conclude that development is the result of variable gene activity?

Question 13

Which general genetic process is believed to account for the variety of cellular structures and functions in eukaryotic cells?

A) negative control exclusively
B) RNA processing
C) variable gene activity
D) intron processing
E) maternal environmental activities

Question 14

Explain the differences between differentiation and determination. Provide examples of each process and indicate how each is involved in development.

Question 15

It is often said that development is a two -step process. Which two steps are likely to be referred to here?

Question 16

Define determination and differentiation.

Question 17

Which term refers to the regulatory events that establish an initial specific pattern of gene activity and developmental fate for a given cell?

A) gradient regulated
B) determination
C) lysogen
D) differentiation
E) attenuation

Question 18

In Drosophila, the sequential order of the function of segmentation genes is _.

A) transdeterminal, gap, pair -rule
B) pair -rule, transdeterminal, gap
C) segmentational, helical, spherical
D) gap, pair -rule, segment -polarity
E) gap, segment -polarity, pair -rule

Question 19

Design an experiment that would allow you to determine if a particular nucleus in a
Drosophila embryo is capable of directing development of an entire new fly.

Question 20

Three investigators-Nusslein -Volhard, Wieschaus, and Lewis-won the Nobel Prize for physiology and medicine in 1995 for work they did in 1970 with Drosophila. Briefly describe their findings.

Question 21

What is the significance of the homeodomain? 28)

Question 22

Do Hox gene clusters exist in humans? If so, how many are known to exist? 27)

Question 23

True or False: Differentiation is the process whereby a cell's determined state is expressed. 33)

Question 24

Molecular/structural orientations (gradients) in an egg are thought to play a significant role in development. What is the origin of such gradients? What evidence indicates
that the maternal genotype is involved in providing such gradients?

Question 25

A gene that specifies the fate of a particular anatomical segment in Drosophila is called a(n) _.

Question 26

Give a brief definition of a homeobox. 30)

Question 27

In Drosophila, maternal -effect genes are influential in determining the anterior -posterior organization of the developing embryo.

Question 28

Mutations in the selector genes sometimes form structures in the wrong segment, transforming the antenna of a fly into a leg, for example. What are such mutations called?

Question 29

Segmentation genes, such as the pair -rule class, are inherited through mitochondrial DNA in Drosophila.

Question 30

How do segment polarity genes relate to pair -rule genes? 21)

Question 31

Which class of genes controls the developmental identity of segments along the anterior -posterior axis?

Question 32

What is the general order of genes involved in determining early Drosophila
development?

Question 33

Genetic involvement in development appears to be achieved, at least in part, by variable gene activity.

Question 34

A homeobox gene is one that produces a group of repetitive base sequences such as a VNTR.

Question 35

From a human developmental standpoint, what is the significance of Hox genes? 29)

Question 36

Determination is the process whereby a cell's eventual developmental fate is set. 32)