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Chapter 3

ANTA01 Chapter 3 Notes.docx

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Chapter 3 Notes: The Cell Genetics: the genes structure/pattern of transmission traits from parent to offspring  there are basically two types of cells somatic and gametes Somatic cells: cellular components of body tissue, muscle, bone, skin, nerves, heart and brain Gamete: sex cells involved in reproduction (egg cells and sperm) DNA structure/function  DNA molecule is composed of 2 smaller chains called nucleotides; sugar, phosphate, 4 bases  bases are adenine, guanine, thymine, cytosine [A-T, G-C) Regulatory gene: play an important role in evolution genes that code for the productions of proteins that can influence the action of other genes Chromosome: discrete structures composed of DNA and protein found only in the nuclei of cells  In humans there are 46 chromosomes, 23 pairs  There are 2 types of chromosome, autosome (carry genetic info all physical characteristic except sex) sex chromosome (XY male, XX females)  22 pairs of autosome and 1 pair of sex chromosome Evolutionary Significance of Meiosis  Meiosis occurs in all sexually reproducing organism  Important because it increases genetic variation in population  Sexual reproduction & meiosis enhance the tole of natural selection populations Genetic Principle Discovered By Mendel Gregor Mendel (1822-1884) -> heredity What: Mendel worked with garden peas concentrating on 7 different traits each expressed in 2 different ways Hybrids: offspring of mixed ancestory (heterozygote) Mendel’s Principle of Segregation  tall and short plant, results -> different expression of a trait controlled by discrete units or particles now genes Principle of segregation (Mendels first principle of inheritance) Genes (alleles) occur in pairs. During gamete production, the members of each gene pair separate, so that each gamete contains one member of each pair. During fertilization, the full number of chromosomes is restored, and members of gene or allele pairs are reunited. Relates to meiosis Dominance and Recessiveness Dominant: describing a trait governed by an allele that can be expressed in the presence of another, different allele (i.e., in heterozygotes). Dominant alleles prevent the expression of recessive alleles in heterozygotes. (Note: This is the definition of complete dominance.) Recessive: Describing a trait that is not expressed in heterozygotes; also refers to the allele that governs the trait. For a recessive allele to be expressed, there must be two copies of the allele (i.e., the individual must be homozygous). Genotype: The genetic makeup of an individual. Genotype can refer to an organism's entire genetic makeup or to the alleles at a particular locus. Locus: position on a chromosome where a given gene occurs. The term is sometimes used interchangeably with gene. Heterozygous: Having different alleles at the same locus on members of a chromosome pair. Homozygous: Having the same allele at the same locus on both members of a chromosome pair. Phenotypes: The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes. Mendel’s Principle Of Independent Assortment:  Traits aren’t necessarily inherited together 50:50  Ratio came out as predicted because loci governing most of the traits he chose were carrid on different chromosomes. Principle of independent assortment: The distribution of one pair of alleles into gametes does not influence the distribution of another pair. The genes controlling different traits are inherited independently of one another.  1866 Mendel’s results were published wasn’t appreciated Mendalian inheritance in Humans Mendelian traits: Characteristics that are influenced by alleles at only one genetic locus. Examples include many blood types, such as ABO. Many genetic disorders, including sickle-cell anemia and Tay- Sachs disease, are also Mendelian traits, one locus  described in terms of frequency within populations, be analyzed by mode of inheritance  Although some have a visible phenotypic expression most don’t. Known Mendelian characteristics are the results of harmful alleles th  Ex. Mandelian traits in humans is ABO blood group , ABO locus on the 9 chromosome Antigens: Large molecules found on the surface of cells. Several different loci governing antigens on red and white blood cells are known. (Foreign antigens provoke an immune response in individuals.)  Ex. antigen A blood type A  AB dominant O is recessive Codminance: The expression of two alleles in heterozygote. In this situation, neither is dominant or recessive; thus, both influence the phenotype.  Ex blood group AB  Recessive is the lack of a substance usually an enzyme, two copies of recessive allele  Heterozygote’s have one copy of a harmful recessive allele are unaffected called carrier Misconceptions Regarding Dominance and Recessiveness  Recessive alleles do have an effect on the phenotype; Ex. many recessive alleles act to reduce but not e
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