Introduction to Genotype and Phenotype Genetic Terminology Trait

Introduction to Genotype and Phenotype

Genetic Terminology § Trait - any characteristic that can be passed from parent to offspring § Heredity - passing of traits from parent to offspring § Genetics - study of heredity

Genotype is… • our genetic make-up • we cannot see our genes! We get one copy of our genes from our mother and one from our father. The genes on these chromosomes might code for different forms of the same trait. Different forms of genes are called alleles.

Genotype is determined… by how the parent’s alleles combine during reproduction. Here, the mother has only the “a” form of the gene, while the father has only the “A” form of the same gene. In this scenario, the offspring can have only one genotype: Aa

Determining Genotypes Here, each parent has both the “A” and the “a” allele for this gene. The offspring can have any of the following genotypes: AA, Aa or aa Image retrieved from: http: //www 1. geneticsolutions. com/Page. Req? id=3844: 1873

So what? • The genotype of an organism is the code for the physical features of the organism (phenotype) Phenotype is the physical appearance of the organism – For example, the allele, “A” might code for a normal skin pigment, while the “a” allele might code for albinism.

What is the relationship between genotype and phenotype? Image retrieved from http: //www. bbc. co. uk/schools/gcsebitesize/biology/variationandinheritance/0 dnaandgenesrev 5. shtml

Image retrieved from http: //bio 1151. nicerweb. com/doc/class/bio 1151/Locked/media/ch 14/14_06 Phenotype. Vs. Genotype_L. jpg

More Terminology § Genotype - gene combination for a trait (e. g. RR, Rr, rr) § Phenotype - the physical feature resulting from a genotype (e. g. red, white)

How is phenotype determined? Generally, certain alleles of a gene completely override other alleles of the same gene (they are completely dominant). The allele for a tall plant is dominant in this example. If the tall parent has only tall alleles, all of its offspring will receive a tall allele from this plant. Since the tall allele is dominant to the short allele, all of the offspring will be tall. Image retrieved from http: //web. pdx. edu/~cruzan/Kid

Punnett Square Used to help solve genetics problems

Designer “Genes” § Alleles - two forms of a gene (dominant & recessive) § Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) § Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes RR Rr rr Phenotypes RED YELLOW

Genotypes § Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e. g. RR or rr); also called pure § Heterozygous genotype - gene combination of one dominant & one recessive allele (e. g. Rr); also called hybrid

P 1 Monohybrid Cross • • Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr r r R Rr Rr Genotype: Rr Phenotype: Phenotype Round Genotypic Ratio: All alike Phenotypic Ratio: All alike

P 1 Monohybrid Cross Review § Homozygous dominant x Homozygous recessive § Offspring all Heterozygous (hybrids) § Offspring called F 1 generation § Genotypic & Phenotypic ratio is ALL ALIKE

F 1 Monohybrid Cross • • Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds Rr x Rr R RR Rr rr Genotype: RR, Rr, rr Phenotype: Phenotype Round & wrinkled G. Ratio: 1: 2: 1 P. Ratio: 3: 1

Given alleles T(tall) and t(short)… -What are the possible genotypes of a tall plant? -What are the possible genotypes of a short plant? -What would be the phenotype of TT? -What would be the phenotype of tt? -What would be the phenotype of Tt?

In a famous experiment, a man named Gregor Mendel mated pea plants. When he mated a pure bred smooth seed with a pure bred wrinkled seed, he found that the wrinkled seed phenotype only occurred about 25% of the time. This happened because the allele for smooth seeds (S) is dominant to the allele for wrinkled seeds (s). Image retrieved from http: //www. accessexcellence. org/RC/VL/GG/mendel. html