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| Where are genes located? | They are on the chromosomes. |
| What 2 things are required in Mendel's principles of genetics? | 1) Each organism MUST inherit a single copy of every gene from both "parents". 2) When an organism produces its own gametes, those two sets of genes must be separated from each other so that each gamete contains just one set of genes (the 2 sets of genes separate so each gamete ends up with one set.) |
| What is a diploid cell? | It's a cell that contains both sets of homologous (identical) chromosomes. It's represented by 2N [i.e., in fruit flies:2N=8, meaning that each of the fruit fly's body cells has 8 chromosomes--2 complete sets of chromosomes and 2 complete sets of genes (one from "mom" & one from "dad").] |
| What is a haploid cell? | It's a cell that contains only a single set of chromosomes and therefore only a single set of genes. (Gametes of sexually reproducing organisms, including fruit flies & peas, contain only single set of chromosomes, and therefore, only a single set of genes, such as N=4). |
| What is meiosis? | It's a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. (see pg. 276-278 pictures) The humber of chromosomes in each cell is cut in half through separation of the homologous chromosomes. So, you end up with 4 haploid cells genetically different from one another & from the original cell. |
| What happens during meiosis I? | Each chromosome (which has already replicated) pairs with its corresponding homologous chromosome to form a tetrad (which contains 4 chromatids). During this process, the homologous chromosomes exchange portions of chromatids in crossing-over. Then the chromosomes separate, forming 2 new cells, each with 4 chromatids. However, the 2 cells have sets of chromosomes & alleles that are different from each other and from the diploid cell that entered meiosis I. |
| What is crossing-over? | It's the process in which homologous chromosomes exchange portions of their chromatids during meiosis. |
| What happens during meiosis II? | The 2 cells formed during meiosis I (each with 2 chromatids in their chromosome) enter the second meiotic division. The chromosomes line up in the center of the cell, and in anaphase II, the paired chromatids separate. (see 276-277) |
| What is the male gamete called? What is the female gamete called? | Male = sperm; female = egg. (see 278 picture) |
| What is the difference between mitosis and meiosis? | Mitosis results in the production of 2 geneticlly 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 & other 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. |
| What does it mean that some genes are linked? | This means that some genes are inherited together. Thomas Hunt Morgan realized that it was the chromosomes that assorted independently, not individual genes. |
| If 2 genes are found on the same chromosome, does this mean that they are linked forever? | No. During crossing-over in meiosis, genes are sometimes separated and exchanged, producing new combinations of alleles. This accounts for genetic diversity. |
| What important contribution did Alfred Sturtevant make in 1911? | He created the first gene map, showing the relative locations of each known gene on one of the Drosphilia chromosomes. He used recombination rates, measuring the frequencies of crossing-over between genes. He showed that the farther apart two genes were, the more likely the genes were to separate by a crossover in meiosis. So, the frequency of crossing-over in equal to the distance between 2 genes. |
