EVOLUTION Flashcards
What causes variation?
Random assortment
Crossing over
Non-disjunction
Random fertilisation
What is random assortment?
Random assortment of chromosomes during meiosis results in gametes that have a huge number of possible combinations of the chromosomes that originally came from the male parent and female parent.
What is crossing over?
Crossing over of chromatids during meiosis may result in piece of chromatid being broken off and attaching to a different chromatid. This results in a changed sequence, or recombination, of the alleles along the resulting chromosome.
What is non-disjunction?
Non-disjunction is where one or more members of a chromosome pair fail to seperate during meiosis. This results in gametes that have more or less than the correct number of chromosomes. If such gametes are involved in fertilisation, the resulting embryo will have the incorrect number of chromosomes.
What is random fertilisation?
Random fertilisation means that, because each person will produce a huge number of different sperm or eggs with respect to the alleles each contains, and because any sperm can fertilise any egg, there is an almost infinite number of possible combinations of alleles in the offspring.
Explain the Dunkers case study.
In the Dunkers, religion does not allow them to marry outside the group. The allele frequency of ABO, Rh and MN blood groups, mid-digital hair, left or right handed ness and attached to free earlobes was measured. It was found they were similar to present-day Hesse, where they came from.
What are some examples of geographical barriers?
Mountains, oceans, desert, ice.
What are some examples of sociocultural barriers?
Religion, education, race, social and economical status.
Describe Tay-Sach’s disease
Caused by a missing enzyme that results in the accumulation of a fatty substance in the nervous system. Symptoms include; muscle weakness, stiff muscles, fatigue, difficulty swallowing, blindness, deafness. It is RECESSIVE.
How does Tay-Sach’s effect the gene pool.
It impacts individuals of Jewish descent from Eastern Europe. These individuals affected die before reproducing, however heterozygotes are resistant to tuberculosis, which provides a survival advantage as it is common in the area.
Describe Thalassaemia
Less blood cells, it is caused by a mutation of the gene responsible for red blood cells. Symptoms include; decreased oxygen carrying capacity, fatigue, anaemia, heart defects, iron deficiency. It is RECESSIVE.
How does Thalassaemia effect the gene pools?
More mutations are found in gene pool, increases mortality rate. However there is a resistance to malaria, which gives a survival advantage as it commonly effects those in Mediterranean areas, where malaria is prominent.
Describe the cause of sickle-cell anaemia.
It results in red blood cells being sickle shaped. It is caused by a mutation of the gene responsible for the production of normal haemoglobin. The mutant allele responsible for the sickle shape causes the substitution of one amino acid for another during haemoglobin formation.
Describe symptoms and inheritance of sickle-cell anaemia.
Symptoms include; clogged blood vessels, reduced oxygen capacity of RBC, fatigue, shortness of breathe, pneumonia, heart disease and weird shape of RBC. It is RECESSIVE
What is the effect of sickle-cell anaemia on gene pool?
It is common in those of African descent, or those in African locations. It gives a survival advantage to those who are heterozygous as they are resistant to malaria, which is common in the area.
What are the principles of evolution?
- There is a variation of characteristics within a species.
- More offspring of a species are produced.
- Struggle for existence
- Individuals with characteristics best suited to the environment live.
- Natural selection.
- Allele frequencies change to favour one gene.
Explain body stature as a principle of evolution.
Eskimos have long bodies and short limbs. They have a small surface area in relation to body volume, allowing them to lose less heat in cold environments, providing a survival advantage.
Tribal Africans have long limbs and short bodies, having a larger ratio of surface area t body volume, losing heat faster, providing survival advantage.
Explain the process of speciation.
Variation - a population exists on an island, sharing a common gene pool. Isolation - species are divides into two groups, meaning no interbreeding (separate gene pools). Selection - two subspecies begin to form, brings about a change in the gene frequencies. Speciation - changes in gene frequencies may be great enough to prevent production of fertile offspring by interbreeding, two species exist.
Explain the founder effect.
Occur when a small group moves away from its homeland to a totally new area and established a community. Pitcairn Island - nine mutineers, six mean and twelve women Polynesians. Due to isolation, there have been very few alleles introduced from outside. Show less genetic diversity.
