L13: Hox Genes

Hoxc-8 gene

KO mice for this gene have a homeotic transformation from lumbar rib to thoracic rib

Hoxa-3 gene

KO mice for this gene have reduced thyroid/cervical development, but does not qualify as a homeotic transformation

homeobox

a 180 nt sequence of DNA, a common motif to all homC genes and found across life

Hox10 paralogs

a triple knockout mouse has ribs growing from all lumbar and sacral vertebrae, so function is to repress rib development

Hox code hypothesis

every body region expresses a specific subset of the hox genes, which establishes the identity of the body region.

Spatial colinearity

expressed in the same order in space/along the embryo as on the chromosome

Temporal colinearity

expressed in the same timeline sequence as on the chromosome

colinearity principle

gene order on the chromosome correlates with order in the body plan. Very rare, seen in HomC genes of drosophila

homeotic gene

gene that codes for a specific body structure and can produce a homeotic transformation

Homologous genes

general, genes that are similar in sequence and may have a common ancestor

Genetic redundancy

keeping several copies of an important gene in the genome, slightly divergent functions but same general job. Ex: the hox paralogs.

Hox gene

mammalian homeobox genes, very parallel to drosophila homC genes. Found in four clusters a-d, with up to 13 genes per cluster(duplication and loss over evolutionary time). Shows spatial and temporal colinearity

homeotic transformation

one body structure is replaced by another. Ex: antennapedia and ultrabithorax mutants

homeodomain

the 60 AA translated from a homeobox DNA sequence. The part of the TF that contacts DNA

Hom-C complex

the group of original homeotic genes in drosophila, on chromosome 3. Comprised of antennapedia complex and bithorax complex.

Paralogous gene

two genes that are duplicates within the species. Ex: HoxA1, HoxB1, Hoxd1.