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inheritance - Heredity Chromosomes A review Humans have 46...

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Heredity
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Chromosomes: A review Humans have 46 chromosomes that are in 23 pairs within a cell’s nucleus Pairs of chromosomes are called homologous chromosomes Autosomes are the 22 pairs of chromosomes that control traits that do not relate to gender of an individual Sex chromosomes are the 1 pair that contain the genes that do control gender Each set of chromosomes is referred to as a homologous pair . Cells (body cells) that have 46 (2N) chromosomes are called diploid Cells (sex cells) that have only 23 (N) chromosomes not in pairs are called haploid
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All cells in an organism have the same genes, but the timing of expression and the combination of genes determines the activities of a particular cell. For example, mammalian eye and heart cells carry genes that code for rhodopsin, which detects light. However, rhodopsin is expressed only in eyes.
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Rhodopsin requires a 2 nd protein to translate light into a response. This other protein is also produced in the heart, but there it is combined with a 3 rd protein to help coordinate heart muscle activity. So, a protein might serve two different functions depending on its content, indicating that there is much flexibility in the instruction manual for building a living organism
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Figure 19.1 Figure 19.1
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Mutations Mutations in genes lead to different versions, or alleles . Since mutations are chance events, it is reasonable to expect that different families would have slightly different alleles for many genes. Repeated mutations create variation in a population.
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What is a karyotype?
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The cell cycle
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Chromosome structure in mitosis Chromosomes contain both DNA and proteins (collectively called chromatin) Chromosomes that are dividing are made up of 2 identical parts called sister chromatids The sister chromatids are held together at a region called the centromere
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Overview of mitosis A diploid cell makes and divides an exact copy of its nucleus Used in cell growth and cell repair Occurs in body cells 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase
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Overview of meiosis Two nuclear divisions occur to make 4 haploid cells Used to make gametes (egg and sperm) Occurs in sex cells Has 8 phases (4 in each meiosis I & II)
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What is crossing over? Crossing-over is the exchange of genetic information between nonhomologous sister chromatids during synapsis This occurs during prophase I of meiosis and increases genetic variation
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The Inheritance of Traits Meiosis separates homologous chromosome pairs, which then separate independently into each gamete. This explains why siblings, save identical twins, are not identical.
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When homologous pairs are separated, the alleles they carry separate, as well; a process called segregation .
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