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The Source of Heredity Beyond Mendel “Chapter 19” Curriculum Outcomes Key Terms Questions Questions 1-5 page 626 The Importance of Chromosomal Theory Believed heredity traits were found in the blood. The term “pure bloodline” During dark ages laws prohibited dissection of corpses. Physicians and scientists performed dissections secretly in caves. Genes are found in the nucleus of cells. Cytology and Genetics Aristotle suggested that heredity could be traced to the power of the males semen. He believed heredity factors from the male outweighed the female. Mendel’s papers made new speculations that egg and sperm unit to form a new individual. Development of Chromosomal theory Observed that chromosomes come in pairs and they segregate during meiosis. The chromosomes then form new pairs when the egg and sperm unit. Today these factors are known as genes. Discovered humans have 46 chromosomes. The development and refinement of the microscope led to advances in cytology. Chromosomal Theory: Chromosomes carry genes, the units of heredity structure. Paired chromosomes segregate during meiosis. Each sex cell or gamete has half the number of chromosomes found in a somate cell. Chromosomes assort independently during meiosis. This means that each gamete receives one of the pairs and that one chromosome has no influence on the movement of a member of another pair. Each chromosome contains many different genes. Morgan’s Experiments Morgan used the fruit fly to study Mendel’s principles of inheritance. The fruit fly reproduces quickly. Females lay over 100 eggs. Life cycle 10-15 days makes it easy to study many generations. They are small in size. Have many mutations. Noticed a white eyed male among red eyed offspring. Traits that govern eye colour was located on the X chromosome Sex-linked traits – are controlled by genes located on the sex chromosomes. Sex Determination Sex-linked genes are found in humans. Red-green colour blindness determined by a recessive gene located on the X chromosome. Barr Body – are small dark spots of chromatin, located in the nuclei of female mammalian cells. You have 46 Chromosomes. If female you have 23 pairs of homologous chromosomes: 22 autosomes and 2 X sex chromosomes If male you have only 22 pairs of homologous chromosomes and one X and one Y chromosome. Homework Review Questions (old text) Page 500 Questions 1-3 Questions 1-7 page 634 Gender Verification at the Olympics Use a buccal mucosa smear, scraping from inside the mouth. Look for evidence of X and Y chromatin. Summary Gene Linkage and Crossing Over Linked genes – are located on the same chromosomes. Crossing over means that a single gene can change as it passes from one generation to generation. Mapping Chromosomes Gene marker – are often recessive traits that are expressed in the recessive phenotype of an organism. The Markers can be used to identify other genes found on the same chromosome. Map distance – refers to the distance between two genes along the same chromosome. A crossover frequency of 5% means that the genes are 5 map units apart. Summary Gene recombinations in Nature Genes can move to new positions. Barbara McClintock “Jumping Gene Theory” Transposons – are specific segments of DNA that can move along the Chromosome. Homework Review Questions (old text) Page 512 Questions 4-8 Questions 105 page 851 Review questions page 657-659