BIOL1040 Lecture 17: MEIOSIS
23 May 2018
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MEIOSIS
LEARING GOALS
• Sexual reproduction, why?
• Meiosis
• Meiosis I and meiosis II
• Cross Over
MEIOSIS
• Meiosis is a type of nuclear division resulting in cells that have half as many chromosomes as
the parent cell.
o In animals it leads to the formation of eggs and sperm.
o These are the Gametes.
• During Sexual Reproduction, a Sperm and an Egg unite to form a new individual.
o This process is called Fertilization.
• Each Gamete contributes a unique combination of genetic information to the offspring.
• Meiosis leads to offspring that are genetically distinct from each other and from their parents
• In humans this occurs only in the ovaries and testes – gametes (haploid cells, single set of
chromosome, humans = 23) vs diploid cells
SEXUAL REPRODUCTION
• The Changing Environment Hypothesis states that offspring that are genetically different from
their parents (those produced by sexual reproduction) may be more likely to survive and
produce offspring in turn if the environment changes than offspring that are genetically
identical to their parents (those produced by asexual reproduction).
• For example, if a new strain of disease-causing agent evolves, then all of the asexually
produced offspring are likely to be susceptible to that new strain. However, if the offspring are
genetically varied, then it is likely that at least some offspring will have combinations of alleles
that enable them to fight off the new disease and produce offspring of their own.
• Numerous studies support the Changing Environment Hypothesis. Thus, sexual reproduction is
thought to be an adaptation that increases the fitness of individuals in certain environments.
• The hypothesis explains that genetically variable offspring, as the result of meiosis, are more
likely to thrive in environments where parasites and disease are common.
• Sexually reproducing individuals are likely to even have offspring that lack any deleterious
alleles present in the parent.
• Natural selection against deleterious alleles is called Purifying Selection. Over time, purifying
selection should steadily reduce the numerical advantage that asexual reproduction has due
to less energy requirements.
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Document Summary
Sexual reproduction, why: meiosis, meiosis i and meiosis ii, cross over. Meiosis: meiosis is a type of nuclear division resulting in cells that have half as many chromosomes as the parent cell. In humans this occurs only in the ovaries and testes gametes (haploid cells, single set of chromosome, humans = 23) vs diploid cells. For example, if a new strain of disease-causing agent evolves, then all of the asexually produced offspring are likely to be susceptible to that new strain. Sexually reproducing individuals are likely to even have offspring that lack any deleterious alleles present in the parent: natural selection against deleterious alleles is called purifying selection.
