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Human Biology Unit III: INHERITANCE AND HUMAN GENETIC VARIATION Mellon/MCHS Introduction: Humans begin life as just one cell and in adult form contain over 100 trillion cells. Cell Division allows this metamorphosis, and in the process of cell division chromosomes and DNA can be altered. These alterations cause variation, mutations, and genetic disease. Genetics, DNA, and genetic disease are studied in many biotechnology and biological research labs. Techniques such as Recombinant DNA, Fingerprinting, Genetic Engineering and Gene Therapy are utilized to study human DNA and cure genetic disease. Objective: At the end of this unit you should be able to understand the following concepts: Chapter 16 (Chap 17 Red Book): Chapter 18(Chap 19 Red Book): • Mitosis • Chromosomal Basis for • Meiosis Inheritance • Cell division • Sex determination, Xlinked Inheritance Chapter 17(Chap 18 Red Book): • Chromosome mutations • Traits/Alleles • Genetic (vs. Infectious) • Inheritance Diseases • Predicting Offspring • Mendelian Genetics Important Notes: Chapter 16 (Chap 17 Red Book) A. Cell Division Mechanisms Mechanisms Functions Mitosis, cytoplasmic division Bodily growth and tissue repair (somatic cells) Meiosis, cytoplasmic division Gamete formation (egg and sperm) and sexual reproduction (germ cells) B. Chromosomes: • DNA wound around protein (chromatin), condensed into rods during cell division. • 46 found in human cells, 23 from mother and 23 from father Chromosome (unduplicated) from one parent: One duplicated chromosome: chromatid sister chromatid Centromere DNA(Chap 21 Red Book) Chapter 21(Chap 22 Red Book): • Recombinant DNA/cloning • Genetic engineering • PCR/DNA fingerprinting • Gene Therapy Human Biology Homologous chromosomes (one from mom and one from dad) are the same length, shape and carry genes for the same traits. Sex chromosomes (X and Y) are an exception—they do not carry the same traits. Karotype: lining up chromosomes by size (23 pairs (diploid 2N=46) in the duplicated state. Mellon/MCHS • • Cell cycle: Interphase G1: period of growth, DNA is not duplicated S: DNA is duplicated G2: Cell prepares for division A. Mitosis is only one phase of the cell cycle B. KNOW THE GENERALIZED CIRCULAR CELL CYCLE FOR THE QUIZ Mitosis A. Mitosis: four stages “PMAT” B. Bipolar Spindle, composed of microtubules, positions the chromosomes and moves them to specific locations during these stages. C. Stages: Prophase: when chromosomes become visible, kinetochore=attachment site for spindle Metaphase: nuclear envelope breaks and chromosomes line up Anaphase: spindle fibers pull sister chromatids apart Telophase: chromosomes are released from spindle, nucleus begins to form in two daughter cells. Cytokinesis A. Division of cytoplasm and cell splitting at telophase. B. Cleavage furrow, depression on the cell surface, appears as the cell divides in two. Meiosis A. Meiosis is a reductional division that halves the number of chromosomes for sexual reproduction. B. Male germ cells are spermatogonia and female are oogonia (1N sperm or egg). C. Meiosis consists of two divisions (two PMATs) meiosis I and meiosis II. D. DNA is replicated during interphase before meiosis I PMAT but not replicated between meiosis I and meiosis II. REVIEW THE DRAWINGS OF MEIOSIS FOUND IN YOUR TEXTBOOK. THESE DRAWINGS WILL BE ON THE QUIZ. YOU WILL HAVE TO IDENTIFY EACH OF THEM, AND DEFINE WHAT IS GOING ON IN EACH DRAWING OF MEIOSIS 1 AND MEIOSIS II. Mellon/MCHS Human Biology E. Crossing over: In prophase I, chromosomes break and recombine giving rise to new combinations of genes. This is called “genetic recombination.” F. Sister chromatids from parents randomly align during metaphase I causing new combinations in gametes. (See fig 16.13) G. Males produce 4 sperm, Females produce one egg and 3 polar bodies. (See 16.14) Questions for Chapter 16: (CHAPTER 17 RED BOOK) 16.1.What does reproduction mean? 16.2.What are the stages of the cell cycle? 16.3.How did HeLa cells come to be used in laboratories all over the world? (Paragraph) 16.4.Draw, describe, and label the four stages of mitosis. (1 page) 16.5.What does the spindle do? 16.6.What is cytokinesis and a cleavage furrow? 16.7.How many chromosomes do body cells (somatic) have? How many chromosomes in sex cells (germ)? 16.8.List briefly the 8 stages of meiosis. 16.9.What is crossing over? 16.10. What is the end product of spermatogenesis and oogenesis? 16.11. What are sources of ionizing radiation (5) and how does it damage cells? 16.12. Compare mitosis and meiosis: where do they occur, what do they produce, how are they similar? (data table) 16.Bonus: Why do offspring look different than their siblings and parents? Human Biology Chapter 17 (CHAPTER 18 RED BOOK) 17.1 Origins of Genetics: Gregor Mendel, an educated monk, was interested in discovering how traits were inherited in offspring. He experimented with the garden pea and based on his research he hypothesized that fertilization united “factors” from each parent that were the units of heredity. Today we call these factors GENES. Mellon/MCHS Terms: Genes: units of information about specific traits passed from parents to offspring. Each has a specific locus on a chromosome. Diploid cells have a pair of genes for each trait, on pairs of homologous chromosomes. Allele: a version of a gene. It can be: Dominant: masks any recessive allele Recessive: must have two recessive alleles to show trait Homozygous: “same” two identical alleles Heterozygous: “different” two different alleles Genotype: alleles present in an individual “what the genes say” Phenotype: an individual’s observable traits “what they look like” Drawing: A pair of homologous chromosomes in the unduplicated state (one derived from a male parent, the other from a female parent. A gene locus: (the location of a particular gene on a chromosome) A pair of alleles (each being a certain molecular form of a gene at a given locus on a pair of homologous chromosomes) Three gene pairs (at three different loci on a pair of homologous chromosomes)--same as three pairs of alleles. 17.2 Mendel’s idea: discrete units of inheritance (genes) 1. Each diploid organism inherits two such units for each trait, one form each parent: 2. Different units assort independently into gametes in parents How is a single trait passed to offspring? Segregation: when homologous chromosomes separate into different gametes the two genes separate.