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| 974898615 | Sex-Linked Traits | -For genes on the X chromosome, women can be homozygous or heterozygous. Men however, have a single X chromosome, and therefore have a single copy of each gene. That single allele, no matter if recessive or dominant, is always expressed. Sex linked recessive traits such a color blindness or hemophilia, or a disease of the blood, are therefore more often found in men than in women. -Genes on the sex chromosomes do not follow Mendelian rules. This is because sex chromosomes do not come in homologous pairs as the autosomes, and because males and females carry different combinations of sex chromosomes, or e.g. in humans, females are XX, males are XY. | |
| 974898616 | Linkage | Linked genes tend to be inherited together. However, during prophase I of meiosis, sometimes homologous chromosomes exchange fragments through of process known as recombination or crossing-over. Particular combinations of alleles can be broken down through recombination therefore generating new phenotypic diversity. | |
| 974898617 | Codominance | When both alleles are expressed: for blood type, a person carrying an allele A and an allele B has blood type AB. | |
| 974898618 | Incomplete Dominance or Semi-dominance | he dominant allele only masks partially the recessive allele. In this case, a heterozygous phenotype is intermediate between the phenotype of a homozygote dominant and a homozygote recessive: a plant with red flowers, bearing two dominant alleles, crossed to a plant with white flowers, bearing two recessive alleles, produce plants bearing pink flowers, bearing a dominant and a recessive allele. | |
| 974898619 | Epistasis | When a gene can alter the effect of a second gene, often masking or preventing its expression. | |
| 974898620 | Pleiotropy | When a gene affects more than a single phenotype. | |
| 974898621 | Most characters have both a genetic and an environmental component. | given genotype might result in a different phenotype depending on environmental conditions. | |
| 974898622 | penetrance | the proportion of individuals with a given genotype that express the expected phenotype. | |
| 974898623 | Molecular Genetics | The study of genes at the molecular level. | |
| 974898624 | Genes have different regions: | Coding regions or exons their sequence is translated into the protein Non-coding regions or introns are regions of DNA within a gene that are not translated into protein Regulatory regions function a kind of control center determining when and how much of the gene should be expressed. | |
| 974898625 | mutations | -During DNA replication, the DNA polymerases occasionally make mistakes. -In order for mutations to be inherited, they must occur in the sex cells, eggs, or sperm. Radiation, chemicals, and even viruses can also induce mutations. | |
| 974898626 | Frameshift mutations | the result of an insertion or a deletion of bases therefore changing the reading frame and the gene product. | |
| 974898627 | Silent mutation | The point mutation does not result in an amino acid substitution, or remember, the genetic code is redundant; in most cases more than one codon codes for the same amino acid. | |
| 974898628 | Missense mutation | The point mutation results in an amino acid substitution, or think miss sense mutation... the "sense" of the protein is missed because the amino acid changed. | |
| 974898629 | Nonsense mutation | The point mutation changes the original codon for a stop codon. The protein might be truncated as its translation was stopped early, or think no sense mutation...the protein doesn't make sense anymore - it was cut short. | |
| 974898630 | Chromosomal inversions | When a large chunk of chromosome is removed, flipped, and the inserted back where it was so. | |
| 974898631 | DNA isolation | CSI and Law and Order have probably taught you all about DNA isolation by now... though the process is significantly more involved than these shows might suggest, it is true DNA can be isolated from the follicle of a single hair, some cells the victim collected under the nails when scratching the assailant, or even some saliva, as long as there are some cells in it. | |
| 974898632 | Polymerase chain reaction | Once you have some DNA, it is possible to make millions of copies of a particular fragment through polymerase chain reaction or PCR. This technique relies on thermal cycling - cycles of steps at different temperatures. First, the DNA is denatured at a high temperature. Second, at a lower temperature specific to the reaction, small fragments of DNA matching the beginning and the end of the fragment of interest are annealed to the two strands of DNA—read as technical term for gluing DNA. Third, a fancy DNA polymerase that only functions at high temperature comes in and extends the fragment from primer to primer using each strand as a template. And then the cycle starts again until thousands of millions of copies of the fragment are produced. | |
| 974898633 | Molecular cloning | It is also possible to make copies of a fragment of DNA using bacteria. First, a piece of DNA is ligated, or a fancy term for sewing together two pieces of DNA to a plasmid, or circular piece of DNA often found in bacteria. Then the plasmid with the extra DNA we want to make copies of is inserted into bacteria. Then the bacteria are left to do what they are best at: grow in numbers really fast. Finally, the plasmid is removed from the bacteria, and the fragment of DNA cut out, often using restriction endonucleases. | |
| 974898634 | Population Genetics | The study of the genetic constitution of populations and how allelic frequencies might change in response to evolutionary forces. Where genetics is, math and evolution come together. But no worries; you won't miss your calculator during the test. | |
| 974898635 | Locus | The location of a gene on a chromosome, or kind of like its "address." | |
| 974898636 | Allele | Different forms of a gene. Say the gene is eye color, an allele is blue eyes, and a different form is brown eyes. | |
| 974898637 | Allelic frequencies | The frequency or proportion, from 0 to 1, of the different alleles at the same locus. Let's look a bit more at what frequency means. If 25% of your hoodies are Abercrombie and Fitch, then 0.25 of your hoodies are Abercrombie and Fitch. You calculate the frequency of A&F hoodies in your closet, or any other frequency, by counting the number of A&F hoodies, or say 3 of your hoodies are A&F, and then dividing it by the total number in the group, or say you own 12 hoodies : 3/12=0.25. Frequencies always add up to 1. You have 0.25 A&F hoodies (3/12), 0.5 The Gap hoodies (6/12), and 0.25 Banana Republic hoodies (3/12): 0.25 + 0.5 + 0.25 = 1. Now, for allelic frequencies, instead of hoodies in your closet, simply picture alleles at the same locus. | |
| 974898638 | Genotypic frequencies | The frequency or proportion, from 0 to 1, of the different genotypes in a population. It is the same theory as for allelic frequencies. But this time, we are talking about combinations of those alleles. For example, at a locus there are two alleles, A and a. The possible genotypes are AA, Aa, and aa. Their frequencies simply tell you the proportion of each; for example, AA = 0.4, Aa = 0.5, aa = 0.1. | |
| 974898639 | Gene pool | The collection of all the different alleles at all loci from a population. | |
| 974898640 | Evolution | off course in pop genetics, the definition of evolution is from a genetics' point of view... changes over time in allelic frequencies in a population. | |
| 974898641 | Hardy-Weinberg equilibrium | describes a population where NO evolution takes place, meaning a population where allelic frequencies do not change over time. It is useful as a starting point to understand what happens when a population evolves. | |
| 974898642 | Hardy-Weinberg equilibrium assumes | A large population size. In a small population, genetic drift (random changes in allelic frequencies due to chance) is likely to occur. Non-overlapping generations. Random mating (vs. individuals picking who to mate with). If not all genotypes reproduce and mix according to their frequencies, allelic/genotypic frequencies in the population are likely to change No mutation. Mutation introduces new alleles No migration or no gene flow. Individuals coming from other populations are likely to change the allelic/genotypic frequencies in the population No natural selection. Differential reproduction of genotypes, or a genetics' point of view of natural selection, would change allelic/genotypic frequencies in the population | |
| 974898643 | The simplest possible scenario is for a single locus with two alleles: | p = frequency of the dominant allele A, q = frequency of the recessive allele a, p + q = 1. | |
| 974898644 | If the population is in equilibrium, we can calculate the frequencies of each genotype: | Frequency of AA = p2, Frequency of Aa = 2pq, Frequency of aa = q2. |
