Chapter 8 The Cellular Basics of Reproduction and Inheritance A Cell Reproduction 1 Mitosis Cell reproduction is responsible for growth the replacement of lost or damaged cells the reproduction of many unicellular organisms and the formation of sex cells 2 Meiosis Sexual reproduction requires the fertilization of an egg by a sperm 3 Before either mitosis or meiosis starts the chromosomes are replicated forming sister chromatids that are joined together at a region known as the centromere B Mitosis 90 of a cell s lifetime is spent in interphase During that time the cells organic compounds and organelles are doubled and the chromosomes are duplicated replicated 1 Stages of Mitosis a Prophaseb Metaphasec Anaphased Telophasee Cytokinesisf Mitosis produces 2 Cancer Cells a A cell cycle control system keeps cells at interphase until receiving a proper signal b When this cycle control malfunctions a benign tumor may form These tumors remain at the original site in the body c Cancerous cells divide excessively 3 Cancer Treatment a Surgery b Radiation therapy Chemotherapy 4 Some cancer prevention methods include early detection of tumors not smoking exercise avoiding excessive sun and proper diet C Meiosis and Sexual Reproduction Human somatic body cells have 46 chromosomes 23 pairs of homologs Homologous chromosomes resemble each other in size and shape and carry the same sequence of genes controlling the same inherited characteristics We inherit one of them from our mother and the other from our father Females have a pair of XX sex chromosomes while the male sex chromosomes are XY Autosomes is the term used to describe the chromosomes other than the sex chromosomes 1 The life Cycle of Sexual Organisms a The somatic cells of humans have 46 chromosomes They have both of each of the homologs and are said to be diploid Gametes or sex cells have only one of each of the homologs and are said to be haploid Human gametes have 23 chromosomes b When a sperm fertilizes an egg a the resulting cell is now diploid 2 Meiosis There are two cell divisions in meiosis a Meiosis l reduction division 1 Prophase l2 Metaphase l3 Anaphase l4 Telophase lb Meiosis ll each of the meiosis l daughter cells goes through the separation of the sister chromatids 1 Prophase II2 Metaphase ll2 Anaphase ll3 Telophase ll3 Genetic Variations a Independent Assortment b Random fertilization gives even more variability to the diploid zygote c Crossing over occurs when homologs exchange segments during prophase l d Non disjunction occurs during anaphase l or ll when chromosomes fail to separate Most of the time human embryos with this condition will abort a Down syndrome occurs when an individual is born with 3 number 21 chromosomes trisomy 21 Chapter 9 Patterns of Inheritance A Introduction Darwin s work left some questions Was blending the way that traits were passed on How to explain the many variations among species Gregor Mendel plant breeder and mathematician In his day nothing was known about chromosomes or genes Pea plants were good to work with small and easy to raise with many easily observable traits self pollinating yet easily crosspollinated and established true breeding strains already available With his mathematical background and complete records of numbers and kinds of offspring he brought new insight into the significance of the statistics he accumulated B Mendel and the Pea Plant 1 Pea plants produced both types of gametes sex cells the egg and the sperm 2 The sperm were in the pollen and the eggs in the ovule 3 Mendel mated true breeding plants with contrasting traits 4 The first generation showed only one of the contrasting traits no blending 5 Crossing 2 of the 1st generation produced a second generation that characteristically had 3 4ths Demonstrating one of the contrasting traits and the other 1 4th showing the other trait C Some Genetic Terms 1 Genes 2 Chromosomes carry many genes 3 Alleles are 4 If the organism is homozygous 5 If the organism is heterozygous hybrid 6 TT homozygous dominant tt homozygous recessive Tt heterozygous 7 The genotype is 8 The phenotype is 9 The original parents are known as the parental or P generation A parental cross produces the first filial or F1 generation while a cross between two of the F1 generation produces an F2 generation D Mendel s Principle of Segregation Experiments with monohybrid crosses 1 Whenever Mendel crossed 2 hybrids Tt x Tt 2 Mendel s principle of segregation E Mendel s Principle of Independent Assortment Experiments with dihybrid crosses 1 When he did dihybrid crosses he predicted the F1 plants would show both dominant alleles all round and yellow 2 He crossed F1 plants to see if the genes for seed color and shape would travel together 3 A 9 3 3 1 phenotype ratio for the F2 generation established that the genes on non homologous chromosomes segregate independently of each other 4 Mendel s principle of independent assortment each pair of alleles segregates independently of the other pairs during gamete formation 5 Test crosses can be used to F Human Genetic Disorders 1 Many disorders are carried on autosomes not the sex chromosomes 2 Examples of these disorders are albinism cystic fibrosis PKU sicklecell anemia and Tay Sachs disease recessive disorders G Beyond Mendel 1 Incomplete Dominance occurs when 2 Multiple Alleles and Blood Type a There are multiple alleles AA AO A blood type BB BO B blood type AB AB blood type OO O blood type b Both A B are dominant to O A B alleles are codominant in that both alleles are expressed in AB individuals 3 Pleiotropy and Sickle Cell Disease a Pleiotropy one gene many traits b Sickle cell anemia commonly inherited by African Americans is an example of this condition The allele is unusually common because heterozygotes for this condition have a greater resistance to the effects of malaria 4 Polymeric Inheritance a Mendel studied monogenic inheritance where there is one gene responsible for the condition b Polymeric inheritance many genes creating 1 trait i e skin color H The Chromosomal Basis of Inheritance 1 The chromosome theory of inheritance states that genes are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patters 2 Gene linkage occurs when some genes are inherited together 3 Crossing over I Sex Chromosomes and Sex Linked Genes 1 Females have XX sex chromosomes while males XY The Y chromosome is 1 3rd the length of the X and only has 1 100th of