Question

8) Bicoid and nano maternal genes play a role in the establishment of body anterior/posterior axes are formed in the fruit fly embryo? c) True d) False 9) What do hox genes act like? f) Control the polarity of the embryo and the formation of the anterior-posterior body axis of many animals (i.e. head to tail formation g) Act as genetic switches that turn on and off other genes, controlling the timing and route of development h) All of the Hox genes share a 180 base pair sequence called homebox and their products have similar functions i) Hox genes from insect and vertebrates are derived from the same ancestral sequences j) All of above 10) Hox genes are present in vertebrate and vertebrates except: f) Anemones g) Flatworms h) echinoderms i) sponges j) Both b and c

Answer 1

1. True.The segmentation of the anterior posterior body plan is established by a set of maternal effect genes. Bicoid  mRNA gets accumulated at the anterior axis and Nanos at the posterior. After fertilisation these are translated into proteins.

Bicoid act as a head morphogen. Nanos help in the formation of abdomen.

These two mRNA creates a gradient. Two other mRNA that are present ubiquitously are repressed along ant-posterior axis by nanos and bicoid.
These two mRNA are hunchback and caudal.

bicoid inhibits caudal and nanos inhibit hunchback expression

hunchback Y caudal → bicoid MRNA snanos MANA aut. post. docyte mRNA caudal hunchback Znanos மென் post embryo proteins

2. All of the above.

Hox genes are subset of homeobox genes. They confers segment identity in drosophila.

14 parasegments of drosophila get their identity :-

8 forms abdomen under HOX genes Abd-a and Abd- b

3 forms mouth

3 forms thorax- T1 forms legs under scr gene

T2 forms legs and wings under Antp gene.

T3 forms legs and halters under Ubx gene.

These are arranged into two clusters of Antennapedia complex (ANT-C) and Bithorax complex(BX-C)

*Sequence of genes activation in Drosophila development:-

-Maternal effect genes establish ant posterior axis and enable gap genes.

- gap genes define broad territories of the embryo and enable pair rule genes.

- pair rule genes divide embryo into segment sized units and activates homeotic genes

-homeotic genes define each segment.

3.Hox genes are studies in invertebrates such as Round worm, Cnidaria,Annelida and molluscs.

so, both b and c would be the correct answer as they are not present in sponges and flatworms.