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genome
all the genetic information of an organism
organisms in the same species share most of their genome
all cells within an organism share the same genome
housekeeping genes
4,000 expressed in nearly all cell types, code for proteins associated with basic cellular functions, such as cell cycle regulation, DNA replication, metabolism
genes that are not housekeeping genes are differentially expressed in different cell types, regulated by proteins that bind to specific base sequences in DNA
methylation
on/off switch of genetic material, regulating access to DNA within a cell
housekeeping genes usually on
differentiation
development of specialized structures and functions in cells
transcription factors
proteins that regulate differentiation in gene expression by binding to specific base sequences in DNA
differentiation during embryonic development
during differentiation of pluripotent cells (ex. embryonic stem cells), DNA methylation enables permanent silencing of some genes
oocyte and sperm → zygote → morula → blastocyst → embryo
morula - ball of cells, undergone 4 cell divisions
pluripotency fades (gradual shutting of DNA) in blastocyst
external environmental conditions can change gene expression
drugs, chemicals, light, temperature
Himalayan rabbits and Siamese cats have temperature sensitive tyrosinase (regulates melanin) controlling fur pigmentation
timing of flowering influenced by photoperiod and temperature patterns
internal environmental conditions
protein hormones do not enter cell, bind to receptors in cell membrane, mediate gene expression through intermediate molecules
steroid hormones enter cell and interact with steroid receptor proteins to control gene expression
tissues
group of cells that have differentiated in the same way to perform the same function
benefits of specialization
focus on fewer tasks at once, work more efficiently
specialized structure and metabolism
do few things all the time, evolve faster in that area