Biology Chapter 13 Meiosis and sexual life cycles
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What is Genetics?
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the scientific study of heredity, and the hereditary variation
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What does heredity involve?
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the transformation of traits from one generation to another
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What is variation?
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is demonstrated by the differences in appearance that offspring show from parents and siblings
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What are genes?
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are the units of heredity, and are made up of segments of DNA
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what is the locus of a gene?
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a gene's specific location along the length of a chromosome
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Asexual reproduction
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a single individual passes genes to its offspring without the fusion of gametes
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Sexual reproduction
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two parents give rise to offspring that have unique combinations of genes inherited from the two parents
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what is a clone?
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is a group of genetically identical individuals from the same parent
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What is a life cycle?
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a generation to generation sequence of stages in reproductive history of an organism
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Alternation of generations
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the alternation of two or more different forms in the life cycle of a plant or animal
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somatic cells
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(any cell other than a gamete) have 23 pairs of chromosomes
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gamete
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a mature sexual reproductive cell having a single set of unpaired chromosomes
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karyotype
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is an ordered display of the pairs of chromosomes from a cell
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homologous chromosome
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two chromosomes composing a pair have the same length, centromere position, and staining pattern
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sex chromosomes
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X and Y chromosomes
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autosomes
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The remaining 22 pairs of chromosomes, not sex chromosomes
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diploid cells
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has two sets of chromosomes, For humans, the diploid number is 46 (2n = 46)
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haploid cells
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A gamete (sperm or egg) contains a single set of chromosomes, For humans, the haploid number is 23 (n = 23)
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fertilization
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the union of two gametes, culminating in the fusion of their nuclei
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zygote
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fertilized egg, one set of chromosome from each parent
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how many cells are present at the end of meiosis I?
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two daughter cells, haploid
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how many cells are present at the end of meiosis II?
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four haploid gametes are produced
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what are the three events unique in meiosis?
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1.Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information 2. At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes 3. At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate
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what is chiasmata?
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The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over
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what is a tetrad?
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A four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids.
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what is the synaptonemal complex?
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A ribbonlike structure consisting of three protein components and extending across the region of synapsed chromosomes during the prophase of meiosis.
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what are the three mechanisms that contribute to most of the genetic variation in each generation of a sexually reproducing organsim?
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1. independent assortment of homologous pairs of chromosomes during meiosis I 2. crossing over which produces recombinant chromosomes 3. random fertilization
