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Diploid cell
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2n, two sets of chromosomes
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Haploid Cell
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n, one set of chromosome
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homologous chromosomes
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duplicate versions of each chromosome, essence of sexual reproduction: each parent donates half its chromosomes to its offspring.
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Gametes
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*sex cells are haploid cells.
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Genetics
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Traits
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The position of a gene on a chromosome is called a locus.
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Diploid organisms
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alleles: two gene copies may be different from one another.
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Homozygous: two identical alleles for a given trait
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Heterozygous: two different alleles for a given trait
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Non Mendelian Genetics
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Linked Genes
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when genes on the same chromosome stay together during assortment and move as a group. (ex: flower color and pollen shape show up together)
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cannot segregate independently, violating Law of Independent Assortment.
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in the unlinked, there are four (TG, Tg, tG, tg), in the linked, there are only two (Tg and tG).
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If a crossover event occurs between linked genes, then recombinant gametes can occur, however, it's unlikely to occur.
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if certain combinations of alleles are found more often in offspring than they should, probably the two genes are close together and linked.
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Recombinants
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offspring formed from recombination events
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frequency of crossing-over between any two linked alleles is proportional to the distance between them, he farther apart two linked alleles are on a chromosome.
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Sex-linked/X-linked traits
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Some traits, such as color blindness and hemophilia, are carried on sex chromosomes.
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most are found on the X chromosome
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A female with one color blind-X is called a carrier
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Barr Body
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X chromosome that is condensed and visible. In every female cell, one X chromosome is activated and the other X chromosome is deactivated during embryonic development.
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Incomplete dominance (blending inheritance
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Traits are blend.
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Codominance
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equal expression of both alleles.
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Polygenic inheritance
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a trait results from the interaction of many genes (height, skin color, weight)
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Non-nuclear inheritance
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genetic material not from nucleus, but from mitochondria or chloroplast. mitochondrial inheritance is always through the maternal(female) line, not the male line.
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Pedigrees
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Traits that skip generations are usually recessive. Traits that appear more in one sex than the other are usually sex-linked.
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Phenotypic plasticity
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two individuals with the same genotype have different phenotypes because they are in different environments
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production of gametes, only sex cells, female gamete (n) + male gamete (n) = zygote (2n)
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more variations in a population, more likely survive extreme changes in the environment.
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Meiosis is far more likely to produce these sorts of variations than is mitosis
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Interphase
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same as miosis
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Meiosis I
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the homologous chromosome pairs separate
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Prophase I
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synapsis: two sets of chromosomes that come together to form a tetrad, then crossing over(exchange of segments) - genetic variaion
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Metaphase I
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line up. the alignment during metaphase is random, so the copy of each chromosome that ends up in a daughter cell is random.
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Anaphase I
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moves to opposite poles.
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Telophase I
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nuclear membrane forms around each set of chromosomes.
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Meiosis II
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to separate sister chromatids, same as mitosis
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Meiotic Errors
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nondisjunctions
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chromosomes failed to separate properly during meiosis. can occur in anaphase I (meaning chromosomes don’t separate when they should), or in anaphase II (meaning chromatids don’t separate).
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translocation
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occurs when a segment of a chromosome moves to another nonhomologous chromosome.
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