genetic control of body plan development Flashcards
what is a homeobox sequence
sequence of 180 base pairs found within genes that are involved in regulating patterns of anatomical development in animals, fungi and plants
what are Hox genes
subset of homeobox genes, found only in animals; involved in formation of anatomical features in correct locations of body plan
what is apoptosis
programmed cell death
what is the meaning of conserved
has remained in all descendent species throughout evolutionary history
why do homeobox genes provide evidence of gene conservation
they are the same order, similar in all organisms and shown to be conserved from ancient ancestors
how does a homeobox gene sequence work
-homeotic genes control anatomical develompent and contain homeobox sequences (DNA) which code for homeodomain sequences (protein)
homeodomain is a transcription factor which can bind to the DNA due to its shape. = recognises TAAT sequence of enhancer region of a gene to be transcribed = enhances transcription
enhancer region = starting point on the DNA for transcription
hox do hox genes work
-found only in animals
-regulated development of embryo along head-tail axis
-control which body part grows where
-body is segmented and develops according to which genes are expresses
explain hox genes in action
code for Homeodomain protein (transcription factor) which
-promotes mitosis:
zygote to embryo to fully grown adult, ensures daughter cells contain full genome
-promotes apoptosis:
programmed cell death
-promote cell migration
-regulate the cell cycle
what are hox genes regulated by
gap genes which first genes that act in development of the embryo from blastocyst, regulated by maternally supplied mRNA found in the egg cytoplasm
how are mitosis and differentiation crucial to the development of an organism
-both involved in development of body plans, create bulk of body parts which are refined by apoptosis by removing unwanted structures under control of expresses genes
explain the steps in apoptosis
1)enzymes break down cytoskeleton
2)cytoplasm becoes dense with organelles and cell surface membrane changes and blebs appear
3)chromatin condenses and nucleus breaks down, DNA breaks into fragments
4)cell breaks into vesicles which are phagocytosed/ endocytosised
how is apoptosis regulated and what are possible stimuli
-cell signals control apoptosis
-internal and external stimuli e.g stress
-signalling molecules include cytokines, hormones, nitric oxide, growth factors
what could happen if there is not enough or too much apoptosis
not enough- tumour formation, cancer
too much- tissue death, too many cells removed
hox genes code for transcription factors and control the development of body plans, explain how failure of the control mechanism during development can lead to webbed fingers
- hox gene does not produce transcription factor
- molecules signaling apoptosis not produces
- apoptosis doesn’t occur to separate the fingers
