HELP PLEASE 1. Describe Mendal\'s law of independent assortment inreference to t
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HELP PLEASE 1. Describe Mendal's law of independent assortment inreference to the dihybrid cross, we performed with corn. Color gene: Purple allele-R Yellowallele-r Shape(taste) gene: Round(strachy)=Su Wrinkled(sweet)=su 2.Describe three exceptions to Mendel's models of heredity.Include Both animal and plant examples with these exceptions HELP PLEASE 1. Describe Mendal's law of independent assortment inreference to the dihybrid cross, we performed with corn. Color gene: Purple allele-R Yellowallele-r Shape(taste) gene: Round(strachy)=Su Wrinkled(sweet)=su 2.Describe three exceptions to Mendel's models of heredity.Include Both animal and plant examples with these exceptionsExplanation / Answer
The principles of heredity were written by the Augustinian monkGregor Mendel in 1865. Mendel discovered that by crossing whiteflower and purple flower plants, the result was not a hybridoffspring. Rather than being a mix of the two, the offspring waspurple flowered. He then conceived the idea of heredity units,which he called "factors", one which is a recessive characteristicand the other dominant. Mendel said that factors, later calledgenes, normally occur in pairs in ordinary body cells, yetsegregate during the formation of sex cells. Each member of thepair becomes part of the separate sex cell. The dominant gene, suchas the purple flower in Mendel's plants, will hide the recessivegene, the white flower. After Mendel self-fertilized the F1generation and obtained the 3:1 ratio, he correctly theorized thatgenes can be paired in three different ways for each trait; AA, aa,and Aa. The capital A represents the dominant factor and lowercasea represent the recessive.
Mendel stated that each individual has two factors for eachtrait, one from each parent. The two factors may or may not containthe same information. If the two factors are identical theindividual is called homozygous for the trait. If the two factorshave different information, the individual is called heterozygous.The alternative forms of a factor are called alleles. The genotypeof an individual is made up of the many alleles it possesses. Anindividual's physical appearance, or phenotype, is determined byits alleles as well as by its environment. An individual possessestwo alleles for each trait; one allele is given by the femaleparent and the other by the male parent. They are passed on when anindividual matures and produces gametes: egg and sperm. Whengametes form, the paired alleles separate randomly so that eachgamete receives a copy of one of the two alleles. The presence ofan allele doesn't promise that the trait will be expressed in theindividual that possesses it. In heterozygous individuals the onlyallele that in expressed is the dominant. The recessive allele ispresent but its expression is hidden.
Mendel summarized his findings in two laws; the Law ofSegregation and the Law of IndependentAssortment.
The Law of Segregation states that when any individual producesgametes, the copies of a gene separate, so that each gametereceives only one copy. A gamete will receive one allele or theother. The direct proof of this was later found when the process ofmeiosis came to be known. In meiosis the paternal and maternalchromosomes get separated and the alleles with the characters aresegregated into two different gametes.
The Law of Independent Assortment, also known as "InheritanceLaw", states that alleles of different genes assort independentlyof one another during gamete formation. While Mendel's experimentswith mixing one trait always resulted in a 3:1 ratio (Fig. 1)between dominant and recessive phenotypes, his experiments withmixing two traits (dihybrid cross) showed 9:3:3:1 ratios (Fig. 2).But the 9:3:3:1 table shows that each of the two genes areindependently inherited with a 3:1 ratio. Mendel concluded thatdifferent traits are inherited independently of each other, so thatthere is no relation, for example, between a cat's color and taillength. This is actually only true for genes that are not linked to eachother.
Independent assortment occurs during meiosis I in eukaryotic organisms,specifically metaphase I ofmeiosis, to produce a gamete with a mixture of theorganism's maternal and paternal chromosomes. Along with chromosomalcrossover, this process aids in increasing genetic diversity byproducing novel genetic combinations.
Of the 46 chromosomes in a normal diploidhuman cell, half are maternally-derived (from the mother'segg)and half are paternally-derived (from the father's sperm). This occursas sexualreproduction involves the fusion of two haploid gametes (the eggand sperm) to produce a new organism having the full complement ofchromosomes. During gametogenesis -the production of new gametes by an adult - the normal complementof 46 chromosomes needs to be halved to 23 to ensure that theresulting haploid gamete can join with another gamete to produce adiploid organism. An error in the number of chromosomes, such asthose caused by a diploid gamete joining with a haploid gamete, istermed aneuploidy.
In independent assortment the chromosomes that end up in anewly-formed gamete are randomly sorted from all possiblecombinations of maternal and paternal chromosomes. Because gametesend up with a random mix instead of a pre-defined "set" from eitherparent, gametes are therefore considered assorted independently. Assuch, the gamete can end up withany combination of paternal or maternal chromosomes. Any of thepossible combinations of gametes formed from maternal and paternalchromosomes will occur with equal frequency. For human gametes,with 23 pairs of chromosomes, the number of possibilities is 2^23or 8,388,608 possible combinations.[3]The gametes will normally end up with 23 chromosomes, but theorigin of any particular one will be randomly selected frompaternal or maternal chromosomes. This contributes to the geneticvariability of progeny.
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