Evolution 2 Flashcards
What can you say about this type of variation compared to the variation in other traits? (2)
A trait referred to as polygenic is one that is regulated by several non-allelic genes. Polygenes are the name for these genes. They are a collection of genes that, when activated, express themselves collectively. Each of these has a cumulative effect that results in the characteristic. However, it can be challenging to discern between the effects of different genes, particularly when a polygenic
feature comprises multiple genes. A trait that is influenced by two or more genes, such as height or skin tone, is referred to as a polygenic trait. Polygenic traits do not follow the laws of Mendelian inheritance since several genes are involved. Polygenic traits are many polygenic qualities that are additionally influenced by the environment.
What factors, other than genetics, influence a person’s height? (2)
Nutrition, hormones, activity levels, and medical issues are just a few of the additional elements that might affect height during growth. Hormones made by the body tell the growth plates to form new bones. These include the pituitary gland’s production of growth hormones, thyroid
hormones, and sex hormones. Growth is greatly impacted by nutrition. Children who have appropriate nutrition may grow taller than those who do not. Children and teenagers benefit from sleep in terms of growth and development. The hormones required for growth are released by the
body when deep asleep. Thus, getting adequate sleep might facilitate proper development. Regular exercise is essential for healthy physical growth. For instance, playing outside or participating in sports can help bones become stronger, denser, and healthier. Sex also influences
a person’s height; males tend to be taller than females. Males may also continue growing for longer than females.
Can you think of any ways in which the extremes of height have been selected against? (2)
The more severe phenotypes are typically eliminated through stabilizing selection, which leads to the reproductive success of the average or typical phenotypes. The population undergoes stabilizing selection when selective pressures choose between two extremes of a trait. For instance, stabilizing selection may have an impact on plant height. If a plant is too short, it might not be able to compete for sunlight with other plants. Extremely tall plants, however, might be more vulnerable to wind harm. When these two selection forces are combined, medium-height plants are maintained. While the number of short and tall plants will decline, the number of medium-height plants will rise. This example also extends to humans as most humans tend to be average height- not too many really short ones or really tall ones.
What would expect the frequencies for the above to be in the next generation?
As allele frequency is constant, according to Hardy and Weinberg, the frequency will remain the same.
What factors would cause you to put forward a different answer? (5)
Immigration and emigration from the sample
Mating between organisms is not random
Sample may not be large enough
A net mutation of a specific gene
Natural selection may wipe out a certain allele
Do laws prohibiting marriages between brothers and sisters make biological sense? Why/ why not? (3)
Yes, it does make biological sense. According to various research, there is a higher chance of producing a kid with potentially fatal birth abnormalities if the parents are closely related. This is due to the fact that some genetic traits—known as recessive genes—remain dormant within a family. These once dormant recessive (ineffective) genes double when two people with the same genes marry and
have children, increasing the likelihood that the offspring would have genetic defects. Additionally, because the DNA of the parents is so similar, this could result in dangerous mutations that impair muscle or cognitive function or create other undesirable problems.
Comment on this statement: “The use of a new antibacterial drug may result in the development of
a new type of bacteria which are resistant to the drug”. (4)
When natural selection and the “survival of the fittest” are observed, this is true. It is possible to understand the phenomenon of antibacterial antibiotic resistance. when common, non-resistant bacteria are revealed and eliminated by antibiotics. Bacteria that have the drug-resistant gene will endure and procreate, passing on the resistance gene. This is evident in diseases like
tuberculosis, where drug-resistant bacteria persist and are permitted to multiply, leading to the development of DR TB, MDR TB, and XDR TB.
Kettlewell, who did the original work on Biston betularia has been accused of fiddling his data, has Haeckel who published work on comparative embryology. Do you think this “fraud” undermines the Theory of evolution? Explain why.
The fact that Kettlewell manipulated his comparative embryology data was revealed, which may have
raised questions about the validity of his hypothesis and ultimately the more general theory of evolution. Despite this, there are numerous additional plausible examples of evolution, such as Darwin’s finches. This demonstrates that the theory of evolution as a whole cannot be disproved
by this one flawed theory in the face of numerous other proofs.
Cystic fibrosis is a fatal autosomal recessive genetic disorder, prevalent in Caucasians, caused by a mutation of a particular gene (cystic fibrosis transmembrane conductance regulator CFTR). This gene is required to regulate the components of sweat, digestive
juices and mucous. People with cystic fibrosis are characterised by having an accumulation
of thick sticky mucous, frequent chest infections and coughing. While this disorder is
fatal, it has survived in the human population for at least 52 000 years and there is some
evidence that having this disease protects against diarrhoea.
Based on your knowledge of natural selection, why do you think this disease has persisted in the population, despite its deleterious effects? Hint: Think about diseases that cause diarrhoea and think about how recessive alleles are carried in a population.
Genes often only persist throughout the history of a species if they help the species survive. This makes sense when you consider how many generations this gene can be passed along. Cystic fibrosis patients typically live to be 30 to 40 years old (which is well into reproductive age). This gene’s ability to prevent diarrhoea is one of its characteristics. Diarrhoea was a symptom of numerous deadly diseases that claimed countless children and adults throughout human history, including cholera. Therefore, the fact that people with cystic fibrosis were immune to diarrhoea and were able to live to reproductive age while
passing on their defective CFTR gene is evidence of the gene’s survival. The gene has therefore
survived.
Do you think your class is a reasonable accurate sample of an ideal randomly mating population? Why / Why not? (2)
N/A
Hardy and Weinberg discovered that sexual reproduction alone will not change the proportions of alleles in a population. This is provided that: (5)
- There is no natural selection against either allele (or no difference in natural selection).
- Mating between members of the population must be random.
- The population must be large enough to ensure each generation represents a random sample.
- There must be no net mutation of one allele to another.
- Individuals must not enter or leave the population through emigration or immigration.
p =
q =
p = proportion of dominant alleles in a population (A)
q = proportion of recessive alleles in a population (a)
Therefore, p + q = 1 =
total alleles in a population (A + a = 1)
= proportion of the dominant phenotype in a population (AA + Aa)
p2 + 2pq
= proportion of the recessive phenotype in a population (aa)
q2
