Deck 21: Developmental Genetics and Immunogenetics

Question 1

The ability to clone plants and animals from single specialized cells demonstrates that genes are not lost or permanently altered during development.
-Scientists have cloned some animals by injecting a nucleus from an early embryo into an enucleated egg cell. The resulting animals are genetically identical with the donor of the nucleus. Does this outcome prove that genetic material is not lost during evelopment? Why or why not?

Answer 1

No, it does not prove that genetic material is not lost during development, because differentiation has not yet taken place in an early embryo. The early embryo would likely still contain all its genes and could therefore give rise to a complete animal. The use of specialized cells, such as a cell from an udder, does prove that genes are not lost during development because, if they were lost, there would be no cloned animal.

Question 2

The major axes of development in early fruit-fly embryos are established as a result of initial differences in the distribution of specific mRNAs and proteins encoded by genes in the female parent (genetic maternal effect). These differences in distribution establish concentration gradients of morphogens, which cause different genes to be activated in different parts of the embryo.

-High concentration of which protein stimulates the development of anterior structures?

A) Dorsal
B) Toll
C) Bicoid
D) Nanos

Answer 2

Bicoid

Question 3

When the major axes of the fruit-fly embryo have been established, segmentation genes determine the number, orientation, and basic organization of the body segments.

-The correct sequence in which the segmentation genes act is:

A) segment-polarity genes $\rightarrow$ gap genes $\rightarrow$ pair-rule genes.
B) gap genes $\rightarrow$ pair-rule genes $\rightarrow$ segment-polarity genes.
C) segment-polarity genes $\rightarrow$ pair-rule genes $\rightarrow$ gap genes.
D) gap genes $\rightarrow$ segment-polarity genes $\rightarrow$ pair-rule genes.

Answer 3

gap genes $\rightarrow$ pair-rule genes $\rightarrow$ segment-polarity genes.

Question 4

Homeotic genes help determine the identity of individual segments in Drosophila embryos by producing DNA-binding proteins that activate other genes. Each homeotic gene contains a consensus sequence called a homeobox, which encodes the DNA-binding domain.

-Mutations in homeotic genes often cause

A) the deletion of segments.
B) the absence of structures.
C) too many segments.
D) structures to appear in the wrong place.

Question 5

Plant homeotic genes control the development of floral structures in plants. The products of four classes of homeotic genes interact to determine the formation of the four whorls that constitute a complete flower.

-What types of flower structures would you expect to see in whorls 1 through 4 of a mutant plant that failed to produce both class A and class B gene products?

A) Carpels, stamens, stamens, carpels
B) Sepals, sepals, carpels, carpels
C) Sepals, sepals, sepals, sepals
D) Carpels, carpels, carpels carpels

Question 6

Cells are capable of apoptosis (programmed cell death), a highly regulated process that depends on enzymes called caspases. Apoptosis plays an important role in animal development and is implicated in a number of diseases.

-How does cell death from apoptosis differ from cell death from necrosis?

Question 7

The genes encoding the antibody chains are organized in segments, and germ-line DNA contains multiple versions of each segment. The many possible combinations of V, J, and D segments permit an immense variety of different antibodies to be generated. This diversity is augmented by the different combinations of light and heavy chains, the random addition and deletion of nucleotides at the junctions of the segments, and the high mutation rates in the immunoglobulin genes.
-How does somatic recombination differ from alternative splicing of RNA?