In the frog (Xenopus laevis)

A gradient of the paracrine factor activin (a morphogen), causes concentration-dependent expression differences of two genes in unspecified cells.

TLS Online TPP Program

#Id: 7422

#Unit 5. Developmental Biology

In the recessive mutant of Antennapedia, the gene fails to be expressed in the second thoracic segment, and antennae sprout in the leg positions

TLS Online TPP Program

#Id: 7423

#Unit 5. Developmental Biology

Dictyostelia (social amoebas) solitary haploid amoebae live on decaying logs, eating bacteria and reproducing by binary fission.

TLS Online TPP Program

#Id: 7424

#Unit 5. Developmental Biology

Dictyostelium can utilize one of three survival strategies when food starvation-

 Microcyst formation, favoured in dark & wet conditions, or ammonia levels are high.

 Zygote formation, favoured in dark & wet conditions, & is triggered by ethylene produced by the cells. 

Cell aggregation & differentiation

TLS Online TPP Program

#Id: 7425

#Unit 5. Developmental Biology

Cell Aggregation & Differentiation is common to all Dictyostelids. It consists of an interconnected programme of cell movement and cell differentiation.

TLS Online TPP Program

#Id: 7426

#Unit 5. Developmental Biology

During growth, unicellular D. discoideum monitor their cell density relative to that of their bacterial food source by secreting a glycoprotein called prestarvation factor at a constant rate.

TLS Online TPP Program

#Id: 7427

#Unit 5. Developmental Biology

When the ratio of PSF relative to that of bacteria exceeds a certain threshold, cells stop proliferating and initiate the expression of genes that are required for their aggregation.