Those who have Down syndrome have three full copies of chromosome 21, a condition termed primary Down syndrome.

familial Down syndrome Human condition caused by a Robertsonian translocation in which the long arm of chromosome 21 is translocated to another chromosome; tends to run in families.

TLS Online TPP Program

#Id: 10171

#Unit 6. System Physiology – Plant

Gibberellins Enhance Cell Wall Extensibility without Acidification.

Enzyme Expansins and Xyloglucan endotransglycosylase (XET) is involved in gibberellin-promoted wall extension. The function of XET may be to facilitate the penetration of expansins into the cell wall.

TLS Online TPP Program

#Id: 10172

#Unit 6. System Physiology – Plant

Three main classes of mutations affecting plant height have

been selected:

1. Gibberellin-insensitive dwarfs

2. Gibberellin-deficient mutants in which the gibberellin deficiency has been overcome by a second “suppressor” mutation, so the plants look closer to normal

3. Mutants with a constitutive gibberellin response (“slender” mutants)

TLS Online TPP Program

#Id: 10173

#Unit 6. System Physiology – Plant

GAI and RGA proteins normally act as repressors of gibberellin responses. Gibberellin acts indirectly through an unidentified signaling intermediate, which is thought to bind to the regulatory domains of the GAI and RGA Proteins. 

TLS Online TPP Program

#Id: 10174

#Unit 6. System Physiology – Plant

DELLA is feedback regulator

TLS Online TPP Program

#Id: 10175

#Unit 6. System Physiology – Plant

In the absence of gibberellin, 

the DELLA proteins positively regulate GID1, GA20ox, and GA3ox, and negatively regulate GA2ox. 

TLS Online TPP Program

#Id: 10176

#Unit 6. System Physiology – Plant

Conversely bioactive gibberellin and the GID1 receptor enhance DELLA repressor degradation, while GA2ox blocks DELLA repressor degradation