Mendelian Genetics Introduction to Genotype and Phenotype

2 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 copyright cmassengale

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. Image retrieved from

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 Image retrieved from:

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:

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.

Image retrieved from What is the relationship between genotype and phenotype?

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9 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

11 Punnett Square Used to help solve genetics problems

12 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)

13 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: GenotypesRR Rrrr PhenotypesRED RED YELLOW

14 Genotypes  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure  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

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

16 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

17 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Rr x Rr F 1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1 copyright cmassengale

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

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

Mendel and the relationship between genotype and phenotype Click on the link that appears below to see an animation about Gregor Mendel and the relationship between genotype and phenotype **Once you get to the sight, click on animation at the bottom of the page to see the animation!!**

Go to the following link and see how changing the genotype of a fictional dragon will change its phenotype. labs_genophenotype.htm Then go to the following link and watch the video. This may help you remember what you have learned. U