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UNIT 2 ADV. BIO (ASEXUAL REPRODUCTION (VEGETATIVE CLONING (Examples…
UNIT 2 ADV. BIO
ASEXUAL REPRODUCTION
A mode of reproduction by which offspring arise from a single organism and inherit genes from one parent only
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VEGETATIVE CLONING
Examples include; runners, tubers, bulbs, plantlets
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PARTHENOGENESIS
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common in arthropods and rotifers, can also be found in some species of fish, amphibians, birds and reptiles
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EXTERNAL FERTILISATION
Both types of gametes shed into water and the sperm are either carried by currents or swim to the egg
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Shedding eggs and sperm into water is an uncertain method as many sperm may not locate an egg, even if both gametes are shed at the same time and place
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MEIOSIS
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INDEPENDENT ASSORTMENT- results in the production of gametes with varying combinations of maternal and paternal chromosomes. The number of chromo can be calculated vis 2n. Results in new combinations of alleles and increased variation
CROSSING OVER- during meiosis I when homologous chromosomes pair up, the inner non- sister chromatids can cross over at points called chiasma. Resulting in new combinations of alleles and increased genetic variation.
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GENETIC DRIFT
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Greater impact in smaller, isolated populations as genes are more likely to be lost from the gene pool
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SEX DETERMINATION
MAMMALS- Females have 2 X chromosomes, males have an X and Y.
BIRDS- Male birds have 2 Z chromosomes, females have a Z and W. Eggs produced by females can either have and X or W chromosome inside
Non- genetic sex determination occurs when the sex of an organism can be altered during a sensitive period of time due to external factors such as temperature
Temperature- dependent sex determination is where the temperature experienced by the embryo during incubation determines its sex. Most prevalent in reptiles.
X INACTIVATION
At a certain point in the embryonic development of a female mammal one of the two X chromosomes in each cell inactivates by supercoiling into a barr body
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INTERNAL FERTILISATION
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DISADVANTAGES
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Parents have to care for, protect and provide nourishment for their offspring
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SURVIVORSHIP CURVES
a survivorship curve is a graphic representation of the number of individuals in a population that can be expected to survive to any specific age
TYPE 1- characterized by high survival probability in early and middle life, followed by a rapid decline later in life. Typical of k- selected species that produce few offspring but care for them well.
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TYPE 3- Characterized by the greatest morality early in life with high probability for survival for those surviving in this bottleneck. Characterized for r- species that produce a large number of offspring
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MODES OF SELECTION
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STABILISING- Favors the average phenotype, giving a decease in variation as more extreme traits don't survive
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CO- EVOLUTION
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THE RED QUEEN HYPOTHESIS
Co- evolutionary "arms race" between a parasite and host. Both organisms must "keep running" to stay alive
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Parasites are better able to feed, reproduce and find new hosts and have greater fitness
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MATING SYSTEMS
MONOGAMY
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Chosen strategy when young are more vulnerable, and require both parents for protection and feeding
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SEXUAL REPRODUCTION
The production of new living organisms by combining genetic information from two individuals of two different sexes
Benefits and costs
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Male half unable to produce offspring- the paradox of the male existence of males. Results in slower population increase.
Each parent disrupts a successful genome as only half of each parents genome is passed onto offspring
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EVOLUTION is the change over time in the proportion of an individuals population, this can occur through genetic drift and natural selection.
FOUNDER EFFECT- The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population
BOTTLENECK EFFECT- Occurs when there is a disaster that reduces the population to a small handful. this leaves smaller variation among surviving individuals.
VARIATION- The differences that exist between individuals in a population determined by the alleles that are inherited.
HOMOLOGOUS CHROMOSOMES- are pairs of chromosomes of the same size, cenrtromere position and with the same genes at the same loci
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