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Chapter 2

Chapter 2. Biology and Evolution. Heredity. The transmission of physical (biological) characteristics from parent to offspring . Chromosomes. Long Strands of DNA and a protein found only in the nuclei of cells. The Cell’s Three Dimensional Nature.

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Chapter 2

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  1. Chapter 2 Biology and Evolution

  2. Heredity • The transmission of physical (biological) characteristics from parent to offspring

  3. Chromosomes Long Strands of DNA and a protein found only in the nuclei of cells

  4. The Cell’s Three Dimensional Nature Understanding Physical Anthropology and Archaeology, 8th ed., p. 43

  5. Chromosomes • Each organism has a characteristic number of chromosomes, usually found in pairs. • Humans have 23 pairs. • Genes, the units of heredity, are segments of molecules of DNA (deoxyribonucleic acid) found on chromosomes. • Humans have approximately 30,000 different genes

  6. Genes and Alleles • Gene: A Short section of a Chromosome that codes for a specific trait • Alleles: Genes located on a homologous pair of chromosomes that may code for different versions of the same trait

  7. Genotype • The actual genetic composition of an organism

  8. Phenotype • the observable physical characteristics of an organism • the things you can see • the detectable expressions of genotypes

  9. Mendel’s Law of Dominance and Recessiveness • Dominant alleles are able to mask the presence of recessive alleles. • For example, the allele for type A blood in humans is dominant to the allele for type O blood. • Alleles that are both expressed when present are co-dominant. • An individual with the alleles for type A and type B blood has the AB blood type. Note: A, B, and O are antigens found on surface of red blood cells. The functions of many of the blood group antigens are not known.

  10. Sickle-Cell Anemia • Homozygous Dominant (Hb A, Hb A) • normal hemoglobin* • Homozygous Recessive (Hb S, Hb S) • abnormal hemoglobin • Heterozygous (Hb A, Hb S) • normal and abnormal hemoglobin • normal hemoglobin more abundant *Note: Hemoglobin is a protein in red blood cells carrying oxygen. (Anemia Video: 1:04 mins.)

  11. Clinical Signs and Symptoms of Sickle-Cell Anemia(Homozygous Recessive genotype) • Pain crises • Acute chest syndrome (a life-threatening pneumonia-like illness) • Cerebrovascular accidents (Stroke) • Splenic and renal dysfunction • Susceptibility to infections

  12. Distribution of Malaria and Sickle-Cell Anemia

  13. In areas where malaria was a problem, children who inherited one sickle hemoglobin gene (Heterozygous genotype) had a survival advantage. • Children with the heterozygous genotype were more likely to survive malaria epidemics than children with the homozygous dominant genotype. • They more frequently survived the malaria epidemics they grew up with, had their own children, and passed on the gene- for sickle hemoglobin.

  14. Population, Gene Pool, Evolution • Population: a group of similar individuals that can interbreed. • Gene Pool: Total number of genes in a population. • Evolution: Change in the frequency of genes in a gene pool over time.

  15. Evolutionary Forces • Natural selection - • “Nature” selects those individuals most fit to survive and reproduce. • Changes in the gene pool due to the differential survival and reproduction of individuals of a population. • Mutation - A heritable change in DNA that happens when copying mistakes are made during cell division. • Genetic drift - the effect of chance events on the gene pool of small populations. • Gene flow - the introduction of new alleles from nearby populations.

  16. Skin Color Factors • Melanin – a pigment in skin, eyes, hair • Carotene - a copper-colored pigment • Skin Thickness • Reflection of Blood Vessels

  17. Skin Color Distribution

  18. Why is skin color distributed in this way?Natural Selection Dark Skin near the Equator: • Reduces frequency of skin cancer • Reduces likelihood of severe sunburn which interferes with sweating

  19. Melanin screens sunlight passing through skin. • The amount of sunlight passing through skin regulates Vitamin D Production • Which Regulates deposition of Calcium • Fair skin near the Equator • Too Much Calcium > Calcification of soft tissues • Dark Skin far away from the Equator • Too Little Calcium > Rickets; Reduced Size of Birth Canal

  20. Mutation • The Ultimate Source of Genetic Variability • During Human Evolution, some mutations allowed humans to adapt to the environment better, e.g., those that led to bipedalism, increased cranial capacity, reduced tooth-size.

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