A unit of heredity on a chromosome is called a gene. Mendel’s particulate theory states that offspring have characteristics inherited from their parents by genes that are passed from parent to offspring. The offspring receives one gene from each parent (Law of Segregation). Mendel’s Second Law, or the Law of Independent Assortment states that alleles are randomly and individually assorted. The …show more content…
Alleles come in pairs, where one is dominant, masks the other alleles, and one is recessive. The dominant allele is usually represented by an upper case letter, and the recessive by a lower case. Genotype includes all the alleles in the cell, and phenotype is the physical appearance of the trait. Example is that T stands for tall, and t stands for short, so a person with Tt would be tall, or TT would be tall. When allele pairs are identical they are called homozygous, and when they are different, they are referred to as heterozygous. Mendel studied genetics using flowers and pea plants. In a monohybrid, concerning one trait, cross, he crossed a purple (PP) plant with a white (pp) plant, and the offspring were all purple (Pp). He also crossed yellow, smooth peas (YYRR) with green, wrinkled peas (yyrr), which is a dihybrid cross because it involves 2 traits. The offspring of the cross, called F1 offspring because they are the first generation, resulted in 100% round (Rr) and yellow (Yy). The offspring were then intercrossed, and the offspring (F2 generation) resulted in 9:3:3:1 round and yellow (RRYY), round and green (RRyy), wrinkled and yellow (rrYY), and wrinkled and green …show more content…
Sometimes codominance can occur, for example in human blood. Humans have four blood types: A, B, AB, O, which are determined by antigens on the red blood cells. If the red blood cell has antigen A or B, then no antibodies will be produced against the antigen. If a person has antigen-A then the person has type A blood and antibodies clump type B blood cells, and vice versa. If the person has antigen-A and B then the person has AB blood and lacks A and B antibodies. If a person is an O then he/she has antibodies against both A and B. Blood typing is used for identification in forensics, and paternity tests. Blood typing is also used to determine the safety of blood transfusions; type A blood cannot accept type B blood because person A’s blood contain antibodies against antigen-B. Another factor of blood is the Rh factor, a protein on red blood cells, and people can either be Rh-positive or