Principles of genetics
Genetics is the study of inheritable characteristics or traits. Gregor Mendel used mathematics to study the inheritance of traits. Alleles are alternate forms of a gene. In a hybrid organism, the dominant allele is expressed.
The Chromosome Theory of Heredity states that the inheritance of traits is controlled by genes, which are located on chromosomes. The genotype of an organism is all the alleles for a trait, the phenotype is the trait. The Law of Segregation describes how chromosome pairs separate during meiosis. The Law of Independent Assortment states that gene pairs separate independently of each other. The Law of Dominance states that the dominant allele, if present, will be expressed.
Scientists use probability to predict traits in offspring. A Punnett square organizes information in order to make genetic predictions. A Punnett square is a grid for organizing genetic information. It is used to predict the offspring of crosses between two organisms considering only one trait, as the color, size or shape. When you study the inheritance of one trait, you are studying a monohybrid cross (mono=one) To make a Punnett square, you can follow these steps:
1. Choose the parents. Example, Jaguars.
Jaguars can be spotted or black. the dominant trait is spotted, and black is recessive.
2. Represent the gametes:
Establish the traits:
Spotted= S
Black= s
In our example, the alleles of the male are dominant, and the alleles of the female are recessive.
Male: SS
Female: ss
3. Place the alleles of the gametes of one parent in the first row at the top of the grid, and those of the other parent in the first column at the left hand side.
4. Combine the parent alleles inside the boxes.
The letters show the genotypes of the offspring. The capital letter of the alleles must be located first for organization.
s
s
S
S
s
s
S
S
Ss
Ss
Ss
Ss
The genotype shows the two alleles that are iherited from parents. in this example, they resulted:
SS= 0%, 0:4 or 0/4
Ss=100%, 4:4 or 4/4
ss= 0%, 0:4 or 0/4
The phenotype is the showing off of the genotype. In this example, is:
Spotted (SS)= 0%, 0:4 or 0/4
Spotted (Ss)= 100%, 4:4 or 4/4
Black (ss)= 0%, 0:4 or 0/4
Try this...
Compare and contrast some of your traits with your classmates.
Download the attached file on top of the page, and check out your results