essay questions Flashcards
how do steroid hormones work?
- hydrophobic signalling molecules diffuse through the phospholipid bilayer of membranes
- they bind to intracellular receptors in the cytosol/nucleus - these are known as transcription factors
- transcription factors can either stimulate/inhibit transcription once bound to DNA
- examples of hydrophobic signalling molecules are testosterone and oestrogen
- cytosolic hormone - receptor complexes move to the nucleus and bind to DNA and therefore affect gene expression
- these DNA sequences are known as hormone receptor elements (HRE)
- binding influences the rate of transcription with each steroid hormone generally affecting the gene expression of many different genes
drift and selection (10)
natural selection is the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
sexual selection is the non-random selection of alleles which increase an individual’s chance of mating and producing offspring. these alleles may have little survival benefit.
sexual selection can lead to sexual dimorphism which is the difference in characteristics of males and females within the same species
sexual dimorphism is where females are generally inconspicuous and males have more conspicuous markings and structures
sexual selection can be due to female choice and male -male rivalry
genetic drift occurs when chance events cause unpredictable fluctuations in allele frequency from one generation to the next
founder effect is an example of a genetic drift where a few members of a species are separated from the larger population. this causes the gene pool of the smaller population to not be representative of the larger generations.
the bottleneck effect is another example of a genetic drift, this occurs when population size is reduced for a generation. this means that the range of alleles are lowered upon which any subsequent pressure may act.
genetic drift is most important in smaller populations as alleles are more likely to be lost from the gene pool.
