File Name: chromosomes genes alleles and mutations worksheet .zip
They code for the proteins that determine virtually all of a person's characteristics.
DNA Chromosomes Genes. Diseases and Evolution. Lecture Syllabus.
Genes and Chromosomes
Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population. Genetic variation is a measure of the genetic differences that exist within a population. The genetic variation of an entire species is often called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele. For example, a population with many different alleles at a single chromosome locus has a high amount of genetic variation.
Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population. The last three of these factors reshuffle alleles within a population, giving offspring combinations which differ from their parents and from others.
Genetic variation in the shells of Donax variabilis : An enormous amount of phenotypic variation exists in the shells of Donax varabilis, otherwise known as the coquina mollusc. This phenotypic variation is due at least partly to genetic variation within the coquina population. Low genetic diversity in the wild cheetah population : Populations of wild cheetahs have very low genetic variation.
Because wild cheetahs are threatened, their species has a very low genetic diversity. Variation allows some individuals within a population to adapt to the changing environment. Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation.
Other new alleles may be immediately detrimental such as a malformed oxygen-carrying protein and organisms carrying these new mutations will die out. Neutral alleles are neither selected for nor against and usually remain in the population. Genetic variation is advantageous because it enables some individuals and, therefore, a population, to survive despite a changing environment. Some species display geographic variation as well as variation within a population.
Geographic variation, or the distinctions in the genetic makeup of different populations, often occurs when populations are geographically separated by environmental barriers or when they are under selection pressures from a different environment.
One example of geographic variation are clines: graded changes in a character down a geographic axis. Gene duplication, mutation, or other processes can produce new genes and alleles and increase genetic variation. New genetic variation can be created within generations in a population, so a population with rapid reproduction rates will probably have high genetic variation.
However, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction. Overall, the main sources of genetic variation are the formation of new alleles, the altering of gene number or position, rapid reproduction, and sexual reproduction.
Apply the law of segregation to determine the chances of a particular genotype arising from a genetic cross. Observing that true-breeding pea plants with contrasting traits gave rise to F 1 generations that all expressed the dominant trait and F 2 generations that expressed the dominant and recessive traits in a ratio, Mendel proposed the law of segregation.
The law of segregation states that each individual that is a diploid has a pair of alleles copy for a particular trait. Each parent passes an allele at random to their offspring resulting in a diploid organism. The allele that contains the dominant trait determines the phenotype of the offspring. In essence, the law states that copies of genes separate or segregate so that each gamete receives only one allele. For the F 2 generation of a monohybrid cross, the following three possible combinations of genotypes could result: homozygous dominant, heterozygous, or homozygous recessive.
The equal segregation of alleles is the reason we can apply the Punnett square to accurately predict the offspring of parents with known genotypes. The behavior of homologous chromosomes during meiosis can account for the segregation of the alleles at each genetic locus to different gametes. As chromosomes separate into different gametes during meiosis, the two different alleles for a particular gene also segregate so that each gamete acquires one of the two alleles.
Independent assortment allows the calculation of genotypic and phenotypic ratios based on the probability of individual gene combinations. Use the probability or forked line method to calculate the chance of any particular genotype arising from a genetic cross. The independent assortment of genes can be illustrated by the dihybrid cross: a cross between two true-breeding parents that express different traits for two characteristics.
Consider the characteristics of seed color and seed texture for two pea plants: one that has green, wrinkled seeds yyrr and another that has yellow, round seeds YYRR. Therefore, the F 1 generation of offspring all are YyRr. For the F2 generation, the law of segregation requires that each gamete receive either an R allele or an r allele along with either a Y allele or a y allele. The law of independent assortment states that a gamete into which an r allele sorted would be equally likely to contain either a Y allele or a y allele.
Thus, there are four equally likely gametes that can be formed when the YyRr heterozygote is self-crossed as follows: YR, Yr, yR, and yr. These are the offspring ratios we would expect, assuming we performed the crosses with a large enough sample size. Independent assortment of 2 genes : This dihybrid cross of pea plants involves the genes for seed color and texture.
Because of independent assortment and dominance, the dihybrid phenotypic ratio can be collapsed into two ratios, characteristic of any monohybrid cross that follows a dominant and recessive pattern. Ignoring seed color and considering only seed texture in the above dihybrid cross, we would expect that three-quarters of the F 2 generation offspring would be round and one-quarter would be wrinkled. Similarly, isolating only seed color, we would assume that three-quarters of the F 2 offspring would be yellow and one-quarter would be green.
The sorting of alleles for texture and color are independent events, so we can apply the product rule. These proportions are identical to those obtained using a Punnett square. When more than two genes are being considered, the Punnett-square method becomes unwieldy. It would be extremely cumbersome to manually enter each genotype. For more complex crosses, the forked-line and probability methods are preferred.
To prepare a forked-line diagram for a cross between F 1 heterozygotes resulting from a cross between AABBCC and aabbcc parents, we first create rows equal to the number of genes being considered and then segregate the alleles in each row on forked lines according to the probabilities for individual monohybrid crosses.
We then multiply the values along each forked path to obtain the F 2 offspring probabilities. Note that this process is a diagrammatic version of the product rule. The values along each forked pathway can be multiplied because each gene assorts independently. For a trihybrid cross, the F 2 phenotypic ratio is Independent assortment of 3 genes : The forked-line method can be used to analyze a trihybrid cross. Here, the probability for color in the F2 generation occupies the top row 3 yellow:1 green.
The probability for shape occupies the second row 3 round:1 wrinked , and the probability for height occupies the third row 3 tall:1 dwarf. The probability for each possible combination of traits is calculated by multiplying the probability for each individual trait. While the forked-line method is a diagrammatic approach to keeping track of probabilities in a cross, the probability method gives the proportions of offspring expected to exhibit each phenotype or genotype without the added visual assistance.
To fully demonstrate the power of the probability method, however, we can consider specific genetic calculations. For instance, for a tetrahybrid cross between individuals that are heterozygotes for all four genes, and in which all four genes are sorting independently in a dominant and recessive pattern, what proportion of the offspring will be expected to be homozygous recessive for all four alleles?
Search for:. Sources of Genetic Variation. Genetic Variation Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population. Learning Objectives Assess the ways in which genetic variance affects the evolution of populations. Key Takeaways Key Points Genetic variation is an important force in evolution as it allows natural selection to increase or decrease frequency of alleles already in the population.
Genetic variation is advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population. Key Terms genetic diversity : the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species crossing over : the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes phenotypic variation : variation due to underlying heritable genetic variation ; a fundamental prerequisite for evolution by natural selection genetic variation : variation in alleles of genes that occurs both within and among populations.
Learning Objectives Apply the law of segregation to determine the chances of a particular genotype arising from a genetic cross. Key Takeaways Key Points Each gamete acquires one of the two alleles as chromosomes separate into different gametes during meiosis. Mendel proposed the Law of Segregation after observing that pea plants with two different traits produced offspring that all expressed the dominant trait, but the following generation expressed the dominant and recessive traits in a ratio.
Key Terms law of segregation : a diploid individual possesses a pair of alleles for any particular trait and each parent passes one of these randomly to its offspring. Learning Objectives Use the probability or forked line method to calculate the chance of any particular genotype arising from a genetic cross. The calculation of any particular genotypic combination of more than one gene is, therefore, the probability of the desired genotype at the first locus multiplied by the probability of the desired genotype at the other loci.
The forked line method can be used to calculate the chances of all possible genotypic combinations from a cross, while the probability method can be used to calculate the chance of any one particular genotype that might result from that cross.
Key Terms independent assortment : separate genes for separate traits are passed independently of one another from parents to offspring. Licenses and Attributions. CC licensed content, Shared previously.
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Most curricular materials in TeachEngineering are hierarchically organized; i. Some activities or lessons, however, were developed to stand alone, and hence, they might not conform to this strict hierarchy. Related Curriculum shows how the document you are currently viewing fits into this hierarchy of curricular materials. A genetic mutation causes white coats in some tigers. Genetic engineers are able to manipulate the genomes of organisms, however, the consequences are not always beneficial.
Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population. Genetic variation is a measure of the genetic differences that exist within a population. The genetic variation of an entire species is often called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele. For example, a population with many different alleles at a single chromosome locus has a high amount of genetic variation. Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population.
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chromosomes genes allele
Explain that the information passed from parents to offspring is transmitted by means of genes which are coded in DNA molecules. Explain how crossing over, jumping genes, and deletion and duplication of genes results in genetic variation. Explain how mutations can alter genetic information and the possible consequences on resultant cells.
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