Dollo’s law:  A biological generalization positing that complex characters, once lost in evolution, are extremely unlikely to reappear and thus the loss of complex characters is virtually always irreversible.

TLS Online TPP Program

#Id: 3328

#Unit 3. Fundamental Processes

The significance of transcription-coupled repair is that it focuses repair enzymes on DNA (genes) being actively transcribed.

TLS Online TPP Program

#Id: 3330

#Unit 3. Fundamental Processes

Central to transcription-coupled repair in eukaryotes is the general transcription factor TFIIH.

TLS Online TPP Program

#Id: 3331

#Unit 3. Fundamental Processes

TFIIH is responsible for two separate functions: 

Its strand-separating helicases melt the DNA around a lesion during nucleotide excision repair (including transcription-coupled repair) and also help to open the DNA template during the process of gene transcription.

TLS Online TPP Program

#Id: 3333

#Unit 3. Fundamental Processes

Humans can exhibit a genetic disorder called xeroderma pigmentosum (XP), an autosomal-recessive disease that renders afflicted individuals highly sensitive to sunlight and results in skin lesions, including skin cancer.

TLS Online TPP Program

#Id: 3335

#Unit 3. Fundamental Processes

Seven genes have been identified in which mutations give rise to XP, these genes specify proteins (such as XPA, XPC, XPD, XPF, and XPG;)

TLS Online TPP Program

#Id: 3337

#Unit 3. Fundamental Processes

In addition to proteins involved in NER, a variant form of XP called XP-V is caused by a defect in the translesion DNA polymerase, Pol h. The gene encoding Pol h is sometimes called XPV. Individuals with XP-V have a milder form of XP.