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| What is a two-factor cross? | It's an experiment in which one follows 2 different genes as they pass from one generation to another. (see Mendel's experiment that followed round yellow peas crossed with wrinkled green peas: (pg. 270-271). |
| What is meant by independent assortment? | It's the independent segregation of genes during the formation of gametes. (In Mendel's experiment: the alleles for seed shape segregated independently of those for seed color). |
| What is the principle of independent assortment? | It states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms. |
| What are the 4 basic principles established by Mendel's experiments? | 1) Inheritance of biological characterisics is determined by individual units known as genes, which are passed from parents to offspring. 2) When 2 or more alleles of a gene for a single trait exist, some are dominant & some recessive. 3) In most sexually reproducing organisms, each adult has 2 copies of each gene (1 from each parent); the genes segregate as gametes form. 4) Alleles for different genes usually segregate independently of one another. |
| What is meat by incomplete dominance? | It's when one allele is not completely dominant over another allele. The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes. (For example, when a red and a white four o'clock plant are crossed, the result is pink flowers). |
| What is meant by codominance? | It's when both alleles of a gene contribute to the phenotype of an organism (what one sees). (see examples pg. 272; erminette chickens & cholesterol levels in humans) |
| What are multiple alleles? | Genes that have more than 2 alleles (i.e., color in rabbits--pg. 273) |
| What are polygenic traits? | These are traits controlled by 2 or more genes. Examples: at least 3 genes are involved in making reddish-brown pigment in eyes of fruit flies; at least 4 genes are involved in skin color. |
| Who was Thomas Hunt Morgan? | In the early 1900's, this geneticist studied fruit flies (Drosophilia melanogaster). He found that all of Mendel's principles applied to organisms other than just pea plants. |
| Are characterisitcs of organisms only determined by genes? | No. Environment plays a role, too. |
| What is the difference between mitosis & meiosis? | Mitosis results in the production of 2 genetically identical diploid cells; meiosis produces 4 genetically different haploid cells. So, in mitosis, a diploid cell that divides results in 2 diploid (2N) daughter cells that have sets of chromosomes & alleles identical to each other and to the parent organism. Asexual reproduction involves only mitosis. In meiosis, a diploid cell produces 4 haploid (N) cells that are genetically different from the diploid cell & from one another. Meiosis is how sexually reproducing organisms produce gametes. |
