BIOLOGY~GENETICS |46 QUESTIONS AND ANSWERS

gene a section of DNA on a chromosome that codes for a protein. alleles one version of a gene. You have one on a chromosome from Mom, the other on the chromosome from Dad. They are represented by capital or lower case letters. dominant allele A version of a gene where you only need one copy in order to express that trait. Represented by a capital letter recessive allele A version of a gene that is not expressed if paired with a different type of allele. Represented by a lowercase letter. homozygous two of the same alleles. If it is two upper case, the trait is dominant, if it is two lower case, the trait is recessive; (RR/rr) heterozygous A genotype with two different alleles. One capital next to a lower letter; the capital is dominant and is next to a recessive allele; (Rr) complete dominance the dominant allele will take over the appearance of the recessive allele when there is an uppercase and a lower case together homozygous recessive Two copies of the recessive allele make up the genotype. When there are two lower case letters together homozygous dominant Two copies of the dominant allele makes up the genotype. There are two upper case letters. genotype The genetic makeup-- the alleles a person has. phenotype How the genotype is expressed in the individual. Punnet Square A tool that is used to determine the likelihood of offspring traits. Genotypic ratio count the number of squares that have the same letter combination Phenotypic ratio count the number of squares that have different physical appearances homozygous x homozygous no ratio; 100% have the same genotype and phenotype Karyotype the number and visual appearance of the chromosomes in the cell nuclei of an organism or species-- used to identify chromosomal abnormalities. Trisomy a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities incomplete dominance two alleles blend together, giving a heterozygote a blended phenotype codominance two alleles share dominance by both expressing themselves polygenic inheritance traits controlled by more than one gene X chromosome Females have two; many genetic diseases are carried on the x chromosome Y chromosome only found in males, smaller than the X chromosome. pedigree chart a way of identifying inheritance patterns in genetic diseases and disorders in a family. No color in shape = normal, half color in shape= carrier, color in shape = disease X-linked (sex-linked) gene found on the X chromosomes; traits more common in males since males only have one copy of the gene. (if they receive the recessive allele they have no dominant allele to mask it). Meiosis process by which 4 reproductive cells are made in a sexually reproducing organism Crossing Over creates variations between gametes, homologous chromosomes mix genes in prophase I. Diploid a cell that contains two copies of every chromosomes. All "autosomal" cells. Haploid a cell that contains half the number of chromosomes of the body cell. Sex cells-- sperm and eggs. gamete sex cell; an egg or a sperm cell 46 human diploid number 23 human haploid number heterozygous x heterozygous results in a 1:2:1 genotypic ratio Blood Types A, B, AB and O. Type O is the universal donor and AB blood is known as the universal recipient. sickle cell anemia an autosomal recessive disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape Cystic Fibrosis autosomal recessive disorder that affects the lungs and digestive system of the individual Huntington's Disease A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms. Hemophilia An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured. Red-Green Color Blindness A common, recessive sex-linked genetic trait. Meiosis I: Prophase I The nuclear membrane dissolves. Chromatin tightly coils up. Homologous chromosomes, each composed of two sister chromatids, come together. Chromatids of homologous chromosomes exchange segments in a process called crossing over. Steps of Meiosis Prophase 1, Metaphase 1, Anaphase 1, Telophase 1, Prophase 2, Metaphase 2, Anaphase 2, Telophase 2 Meiosis I: Anaphase I As the cell moves into anaphase I, the homologous pairs of chromosomes separate. During anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. Meiosis II: Anaphase II Sister chromatids separate, individual chromosomes move toward opposite poles.