Body Plans Flashcards
What is a body plan?
Living organisms come in all different shapes and sizes from tulips to mosquitoes to humans. It is the same small group of genes that control the growth and development of these vastly different living forms. The regulation of the pattern of anatomical development is called morphogenesis.
Describe and explain what a homebox gene sequence is
-they are regulatory genes which control the body plan
-each homebox sequence is a stretch of DNA 180 base pairs long
-each one codes for a sequence of 60 amino acids in a protein, called a homeodomain
-this is a highly conserved sequence in all multicellular organisms
-the homeodomain protein can bind to DNA, switching other genes on or off, and can act as a transcription factor to control the body plan
-these genes are involved in determining the body plan in multicellular organisms
Describe and explain what Hox genes are?
-a particular type of homeobox genes that are only found in ANIMALS
-they are responsible for the positioning of the body parts
-they are found in clusters on particular chromosomes= hox clusters
-mammals have 4 clusters on different chromosomes, the order in which they appear on the chromosomes is the order which they are expressed
-different homeobox genes are activated and expressed at different stages of embryo development
What are the 3 ways homeobox genes determine the body plan?
- The polarity of the embryo (head and tail end)
- The polarity of each segment of the organism
- Which structures develop from each segment (e.g arms, legs etc)
What are the 3 types of symmetry that the body of plan of most animals can have, and give examples of which animals have them,
- Radial symmetry = there is no right or left side, only a top and bottom = jellyfish
- Bilateral symmetry = have both a right and left side and a head and a tail rather than just top and bottom = in most animals e.g humans
- Asymmetry = there are no lines of symmetry = sponges
Explain why homeobox genes have changed very little during evolution
They are so crucial to the body plan of organisms. Any mutations to these genes would result in organisms that don’t function properly, and so don’t survive. The process of natural selection has eliminated most organisms with mutated homebox genes, making them highly conserved
Explain why homeobox genes control the many mitotic divisions through the development of an organism
-ensures that each new daughter cell contains the full genome, and is a clone of the parent cell. During cell differentiation when cells in different parts of the body specialise, certain genes in particular cells are ‘switched on’ and others are ‘switched off’
Explain how the drug Thalidomide taken by pregnant women in the 1950s had an effect on body plan
The drug affected one or more homeobox genes at a particular stage of embryonic development when their activity was crucial. This resulted in the baby having arms and legs which did not develop properly
Explain what apoptosis is and how it effects the body plan of organisms
-means ‘programmed cell death’ where some cells break down as part of the normal development of an organism
-involved in the development of different parts of the organism before and after birth
-is also involved in the metamorphosis in some species e.g tadpoles change to frogs
What is the process of apoptosis?
- Enzyme breaks down the cell cytoskeleton
- The cytoplasm becomes dense with tightly packed organelles
- Cell surface membrane changes and small protrusions called blebs form
- Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments
- The cell breaks into vesicles that are ingested by phagocytic cells, so that the cell debris does not damage any other cells or tissues- this is a very fast process
Explain how homeobox genes are linked/ control apoptosis
-homeobox genes code for protein transcription factors, these then activate the genes needed for apoptosis e.g coding for enzymes needed for programmed cell death
Give an example of apoptosis happening in humans
During the development of the hands and the feet in the embryo, apoptosis causes the skin begin fingers and toes or break down
What process is important in making sure there is a balance between the rate of cells dying through apoptosis and the cells being produced through mitosis?
Cell signalling
Give 3 examples of internal stimuli that can affect apoptosis during growth and development
-DNA damage
-hormones
-cytokines
Give 3 examples of external stimuli which can affect apoptosis during growth and development
-infections by pathogens
-changes in temperature
-changes in light intensity (seasonal change)
-stress- anything that can disrupt the homeostatic balance within the body
