Patterns in Development Pattern formation must be established via induction prior to morphogenesis. The pattern formation is related to the body plan (its 3-D shape) for that specific organism. In animals pattern formation is limited to embryos and young juveniles. – Plants - morphogenesis and pattern formation continue throughout the life of the plant. – Animals - major axis are determined first(ventral/dorsal, anterior/posterior, & right/left) the major axis make up the positional information

drosophila development – maternal effect genes(egg-polarity genes) determine the axis of development in the ovum bicoid- maternal gene responsible for establishing the anterior portion of the embryo – bicoid is concentrated at the anterior portion of the egg before fertilization – mutated bicoid results in 2tails – Bicoid at both sides results in 2heads Maternal effect genes set off a cascade of embryo segmentation-genes during development – products are often transcription factors & signal molecules that set off the next set of genes – examples of segmentation-genes are » Gap-genes - regulate pair-rule genes » Pair-rule genes - activate segment-polarity genes » Segment-polarity genes - determines the boundaries and axis Identity of the segments are determined by homeotic genes – specify the appendages that form on the individual segments

Plants - root/shoot axis is determined first – not as many model organisms as much less resources are dedicated to plant research – positional information is more important than cell lineage (many cells are totipotent) – cell-signaling (induction) and transcription regulation drive development the embryonic development occurs inside the seed post embryonic differentiation is controlled at the apical meristem

Cell lineage Cell lineage is a term that describes the connection between the differentiated cell and the cells that it came from. Two main factors contribute to the cell lineage: Induction - signals between cells influence the differentiation of nearby cells Apoptosis - Programmed cell death – mechanism is essential in the development of the embryo – when the signal is received the cell shrinks becomes lobed (blebbing), the nucleus condenses and the DNA is fragmented. Neighboring cell engulf and digest the remains. – necessary for the development of the nervous system, operation of the immune system, and morphogenesis of the hands and feet

Homeobox Comparisons of embryos leads to clues of evolution. With modern genomic techniques, researchers are discovering how minor environmental pressures can lead to morphological changes in a species. Study of many animal genomes led to the discovery of similar sequences of developmental genes called the homeobox. 180 nucleotide sequence common in the homeotic genes (hox genes) of all animals – codes for a 60 AA sequence called the homeo domain of developmental proteins – similar genes are also found in eukaryotic plants and in egg polarity genes (bicoid) suggests the origin is very early in the evolutionary tree