Chapter 4 - BB (1)

A pleiotropic single gene on the phenotype of an

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Unformatted text preview: ects: Multiple effects of a Pleiotropic single gene on the phenotype of an organism. organism. 1. 2. 3. Single gene affect cell function in more than one way. Gene expressed in different cell types. Gene expressed at different stages of development. GENE INTERACTIONS GENE Gene interactions : when two or more different genes influence the outcome of a single trait outcome Types of traits Types Discrete or discontinuous – Clearly defined phenotypic variants – Purple or white flowers, red or white eyes Continuous or quantitative – Majority of traits – Show continuous variation over a range of phenotypes – Height, skin color, number of apples on a tree – Polygenic- several or many genes contribute to the outcome – Environment also plays a role Gene Dosage Effect The inheritance for a single gene depends on the particular allele of the The gene gene X-linked eye color gene in Drosophila X-linked Drosophila Morgan and Bridges found another allele Morgan Eosin – pale orange Eosin pale Homozygous females eosin Homozygous Males light-eosin Males light-eosin difference in intensity - the difference in the number of X chromosomes difference between the male and female between – Female has two copies of the “eosin color producer” allele – Males have only one copy of the allele Two-Gene Interaction - 9:3:3:1 ratio Inheritance of comb morphology in chicken – William Bateson and Reginald Punnett in William 1906 1906 – Comb types - four different morphologies F2 generation : 9 walnut : 3 rose : 3 pea : 1 single comb morphology is determined by two different comb genes genes – R (rose comb) is dominant to r – P (pea comb) is dominant to p – R and P are codominant (walnut comb) and are (walnut – rrpp produces single comb Two-Gene Interaction - 9:7 ratio Inheritance of flower color in the sweet Inheritance pea (Lathyrus odoratus) P: True-breeding p...
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