Bio 1201 Notes

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* Meiosis – cell division for gamete production
* In specialized tissues
* Produces cells with the 1n chromosome number
* Two Divisions
* Meiosis I separates homologous chromosomes
* Meiosis II separates sister chromisis
* Asexual Reproduction
* Mitotic division
* Identical offspring
* Sexual Reproduction
* Fuse gametes from parents (syngamy) to produce a zygote * Each parent contributes half the genetic material
* Increase the diversity of offspring
* Different combinations of chromosomes
* Increase the potential type of diversity
* Stages of Meiosis
* Prophase I
* Metaphase I
* Anaphase I
* Telophase I
* Prophase II
* Interphase
* As in mitosis
* During S phase DNA is replicated giving rise to chromosome consisting * Prophase I
* Spindle formation
* Breakdown of nuclear envelope
* Chromosomes condense
* Each chromosome consists of 2 chromatids from S phase of interphase * Homologous chromosome pairs lie next to one another
* Crossing over of chromatids between pairs (chiasma formation) * Crossing Over
* Called chiasma (chiasmata – plural)
* Hold homologous chromosomes together
* Can result in a physical exchange of genetic material between homologs * Recombinant chromosomes result
* Increase genetic diversity
* Meiosis
* Occurs in cells that give rise to gamets
* Produces cells with the haploid (1n) chromosome number
* Mitosis occurs in somatic cells and produces diploid (2n) cells * Metaphase I
* Chromosome pairs line on equator of spindle
* Kinetochores of sister chromatids are attached to fibers going to the same pole * Anaphase I
* Homologous chromosome pairs separate
* Sister chromatids remain together
* Telophase I
* Depending on the species
* Nuclear membrane may reform
* Cytokinesis may occur
* Meiosis II
* Cell division like mitosis but starting with the haploid chromosome complement * Sister chromatids are separated
* Gamete formation in human males
* Spermatogenesis in diploid reproductive tissues
* Spermatocytes (2n) undergo meiotic divisions and produce spermatids (1n) * Gamete formation in human females
* Before birth
* Oogonia (2n) give rise to primary oocytes (2n) stopped in prophase I * At ovulation polar body formation gives rise to a large egg. * Mitochondria inherited from mother

* Gossian didn’t count and record his numbers.
* Mendel chose the right organism to work with, the edible pea plant * The plant usually self pollinates
* Stigma and anthens are completely enclosed by petals until after organization * Therefore there is no cross contamination
* Why did Mendel succeed?
* He picked the right traits to follow
* He followed the crossed for several generations
* He was quantitative in his observations
* He had a little help from his friends
* Gene – discrete unit of hereditary information consisting of a specific sequence of DNA * Often codes for a polypeptide chain
* Gene locus
* Particular position along a specific chromosome where a given gene is located * Allele
* Alternative form of a gene eg. A, a
* Genetics problems
* On moodle, questions like on 3rd exam
* Homozygous
* Having 2 identical alleles for a trait
* AA
* Aa
* Heterozygous
* Having 2 different genes (alleles) for a trait
* Aa
* Genotype – the genetic makeup of a material
* Phenotype – the physical manifestation of a trait
* How it appears
* Determined by genotype
* Dominant Allele
* Allele that is fully expressed in the phenotype of a heterozygote * Only a single copy is required to express a trait
* Represented by a capital letter (A)
* Recessive Allele
* In a heterozygous individual...
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