Meiosis

Mesiosis and Fertilization
Paola Cordón Slowing
Centro Escolar Entrevalles, Biology – 11th. Grade
July, 2010
Decoding Punnett
Research questions:
* Is the Punnett Square a truly reliable source?
* What effect does the random assortment of genes during meiosis have on the characteristics of the offspring?
Aim
* To learn about genetics, thus referring to meiosis, genotypes,phenotypes, assortment of genes and the Punnett square.
* Learn to predict certain traits of a baby before he is born by using the Punnett square.
* Prove the reliability of the Punnett square.

Hypothesis
Because the Punnett square works in terms of chance, just a little percentage of the traits will be rightly predicted by it.

Variables:
Independent: The alleles
Dependent: Theresulting traits
Controlled: The alleles placed in the experiment.

Background:
Meiosis is the kind of cell division that, in some organisms, produces special haploid cells called gametes. In meiosis, chromosomes are randomly shuffled. As a result, the offspring of organisms that reproduce sexually have a mixture of both parents’ genes. This variety contributes to the adaptability, and thereforesurvival, of a species. In this lab, you will simulate the random assortment of human genes and explore the variety of genotypes and phenotypes that characterize the offspring. Recall that homozygous-dominant offspring for a trait have received the dominant gene for that trait from both parents. Heterozygous-dominant offspring have the same phenotype as the homozygous-dominant offspring but have aheterozygous genotype. They have received one gamete carrying the recessive gene and another gamete carrying the dominant gene. You will determine genotypes and phenotypes for gender, tongue rolling, earlobes, mid-digital hair, hairline, and thumb shape.
The Punnett square is a mathematical tool used by geneticists to show allelic combinations of gametes and to predict offspring ratios. It isrepresented in a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach, and is used by biologists to determine the probability of an offspring having a particular genotype. The Punnett square is a summary of every possible combination of one maternal allele with one paternal allele for each gene beingstudied in the cross.
When both the alleles of a gene pair are the same, the organism is said to be homozygous for that characteristic. It can be homozygous dominant (GG) or homozygous recessive (gg). When the two alleles in a gene pair are NOT the same, for example, when the genotype is Gg, the organism is heterozygous, or hybrid for that trait. When working with only one trait this condition iscalled a monohybrid. If we were to work with two traits, we would call the combination a dihybrid and so on. We use the term "genotype" to refer to the allele combinations of an organism. Mendel performed a second series of experiments in which he crossed true-breeding plants that differed in two traits; such crosses are appropriately called dihybrid crosses. For example, he crossed tall plantswith yellow seed color with short plants with green seed color. The F1 generation showed the dominant characteristics of being tall plants with yellow seeds. Mendel then allowed the F1 generation to self-pollinate. He found that the four factors segregated into the gametes independently. There were four phenotypes among the F2 plants - tall plants with yellow seeds (TY), tall plants with green seeds(Ty), short plants with yellow seeds (tY), and short plants with green seeds (ty). The dihybrid cross allowed Mendel to deduce the law of independent assortment, which states that the members of one pair of factors segregate independently from another pair. Therefore, all possible combinations of factors can occur in the offspring.

Materials:
*
* 1 pair of scissors
* 1 Glue...