How Sex Leads To Variation Lecture

Scope this lecture continues their discretion of mentors contribution to genetics turned and the subsequent experiments in which Mendel looked at the transmission of more than one trait, leading to an of independent assortment. The lecture summarizes in the wind us up and, linkage, and crossover, all of which result from the way chromosome and the gene located on them move during gamete formation and sexual reproduction. The lecture concludes by recapping the sources that contribute to genetic variation that is essential for evolution to occur.
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Outline






I. Mendel continued his space experiment by crossing pea plants that are too phenotypic differences instead of one. From these dihybrid crosses, Mendel inferred additional properties of three transmission from the parents to offspring, properties consistent with knowledge gained later the moment of genes on chromosomes.

A. as wit flower color, seed color in pea plants depend on the single gene with two alleles: the Dominant yellow allele(Y) in the recessive gene allele(y).
B. space for example, when crossing the female pea plant with purple flowers and yellow seeds with the male pea plant with white flowers and green seats, we know that females genotype is PPYY in the male genotype is ppyy.
C.F1 individuals will have purple flower and a yellow seeds, because they are all heterozygous for both traits. As in monohybrid cross, the recessive traits disappeared in F1.
D. when F1 individuals makes gametes, do the allels from the original parents stay together or are they separated next?

If parent alleles are linked, an F1 space individual could produce only PY and py gametes;F2 would then contain only two parental phenotypes. Furthermore, these people takes would have the same 3:1 ratio as in monohybrid cross. This would mean that sets of parent alleles acted as a single alleles.
If parental alleles are not linked,F1 individuals would produce for better gamete in equal proportions:PY,py,Py,pY. A punnet Square using these gametes asserting 16 possible combinations and 9 distinctive F2 genotypes. These nine genotypes would produce 4 possible phenotypes, which would occur in 9: 3:3:1 ratio. Two of these phenotypes would not have existed in parent the generation; these so-called recombinant phenotypes.
Mendel observed 4 phenotypes in a 9:3:3:1 ratio in his F2 generation, which he correctly concluded to mean that alleles of inherited independently of each other.

E. from this conclusion, mendel formatted what is known as law of independent assortment, which simply says that Alleles off different genes segregating independently of each other during gamete formation.







II. Integral assortment of genes during meiosis is an important source of genetic variation.







During first meiotic division, homologues chromosomes line up in the cell and separated into two daughter cells. The assortment of Maternal and parent homology’s for1 chromosome has more effect on the assortment of any other chromosome.
In the genes of two different traits are on different chromosomes, they will assort independently of each other, as Mendel saw, and independent assortment produce recombinant phenotypes.
The number of unique combination of alleles on different chromosome can be very. Humans have 23 pairs of chromosomes; the possible number of assortment is 2(23) or about 8.4 million.
Independent assortment is different from mutation as a source of variation.
Mutation essentially generates new alleles-usually dysfunctional but not always.
Independent assortment does not create new alleles but, rather, new assortment of alleles.
However, both mutation and Independent assortment can change their phenotypes of successive generations.

III. if two genes occur on the same chromosome, an obvious conclusion is that they will be transmitted together as a unit during meiosis. Such genes are called linked genes.
During meiosis, however, homologue pairs of chromosomes associated so closely that they can exchange genetic material, which called crossing over. If linked gene crossover to other chromosome, they can assort independently.
Geneticists expanding on Mendel's work found that in the Everett tosses, F2 generation with linked genes would occasionally produce recombinant phenotypes, though a far fewer number than if the genes unlinked. Link genes, however, should not produce any recombinant phenotypes.
The further apart to genes on the chromosome, the more likely crossing over and recombinant phenotypes with be.

IV. Space though essentially established the sciences of genetics, Mendel’s work was ignored for about 40 years, because nothing was then known of the physical basis of mentors heritable factors and because he used advanced probability mathematics to calculate is ratio. Only when biologists began to see the pattern Mendel described did anyone realize that this work might be significant.