BIOLOGY inheritance@raffy - Biology Inheritance Activity

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The Chromosomal basis of inheritance.
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It was not until 1900 that biology finally caught up with Gregor Mendel. Independently, Karl Correns, Erich von Tschermak, and Hugo de Vries all found that Mendel had explained the same results 35 years before. Still, resistance remained about Mendel’s laws of segregation and independent assortment until evidence had mounted that they had a physical basis in the behavior of chromosomes. Mendel’s hereditary factors are the genes located on chromosomes. Introduction
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Around 1900, cytologists and geneticists began to see parallels between the behavior of chromosomes and the behavior of Mendel’s factors. Chromosomes and genes are both present in pairs in diploid cells. Homologous chromosomes separate and alleles segregate during meiosis. Fertilization restores the paired condition for both chromosomes and genes. Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles.
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Around 1902, Walter Sutton, Theodor Boveri, and others noted these parallels and a chromosome theory of inheritance began to take form.
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Thomas Hunt Morgan was the first to associate a specific gene with a specific chromosome in the early 20th century. Like Mendel, Morgan made an insightful choice as an experimental animal, Drosophila melanogaster , a fruit fly species that eats fungi on fruit. Fruit flies are prolific breeders and have a generation time of two weeks. Fruit flies have three pairs of autosomes and a pair of sex chromosomes (XX in females, XY in males). Morgan traced a gene to a specific chromosome.
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Morgan spent a year looking for variant individuals among the flies he was breeding. He discovered a single male fly with white eyes instead of the usual red. The normal character phenotype is the wild type . Alternative traits are mutant phenotypes .
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Morgan deduced that the gene with the white-eyed mutation is on the X chromosome alone, a sex- linked gene. Females (XX) may have two red-eyed alleles and have red eyes or may be heterozygous and have red eyes. Males (XY) have only a single allele and will be red eyed if they have a red- eyed allele or white-eyed if they have a white-eyed allele.
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Each chromosome has hundreds or thousands of genes. Genes located on the same chromosome,
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BIOLOGY inheritance@raffy - Biology Inheritance Activity

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