Summary notes – The punnet square and the pea plants of studys PDF

Preview

Summary

Biology notes are useful for exams they can be useful and they can also be used for exam preparations!!...

Description

Summary notes – The punnet square and the pea plants of studys Over the years, with the advancement in the field of genetics, Punnett squares have found use in maternity clinics. These are used by the genetic counselor to help couples make a decision about having children. This is especially useful in cases where the parents are carriers of an autosomal recessive disease. Punnett squares are also used to determine the most effective cross in order to produce pets like dogs and cats with desired traits.

Examples of Punnett Square Seed form in Pea plant The cross between the wrinkled and round seeds in pea plants is an example of a monohybrid cross which can be displayed in a Punnett square. The cross was famously performed by Mendel during his study on pea plants. The Punnett square for this cross begins with the representation of the genotype by alleles. The dominant round form is represented by the capital letter R, whereas the recessive wrinkled form is represented by the lower case letter r. Each of the alleles is segregated independently to form gametes which are then added to the 2×2 table. Punnett square- Seed form in Pea plant Each of the boxes in the grid represents the possible genotypes of the offsprings obtained from the cross. The result of the cross is observed in the form of three heterozygous round seeds and single wrinkled seed. But the genotype ratio remains 1:2:1 with one homozygous round, two heterozygous round, and one homozygous wrinkled seeds. Dihybrid cross in Drosophila An example of 4×4 Punnett square can be observed in the dihybrid cross between the long-winged and black-bodied Drosophila and a vestigial-winged, grey-bodied Drosophila. The cross produces 9 long-winged grey-bodied, 3 long-winged black-bodied, 3 vestigial-winged greybodied, and one vestigial-winged black-bodied Drosophila. The Punnett square for the cross can be observed as below: Punnett square- Dihybrid cross in Drosophila

Limitations of Punnett Square Even though Punetts square has been used as a tool to understand Mendelian genetics, it cannot be used in the cases of complex genetic inheritance.

These cannot accurately determine the distribution of genotypes and phenotypes in the case of linkages. Punnett square is also not useful in studying straits that are determined by multiple genes by varying degrees. The tool is also of no help in the case of genes that are present in the mitochondria or the Ychromosome and are entirely inherited....