NATS 1675 Lecture 9: TOPIC 2- Lecture 9 Notes
6 Feb 2018
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Polygenic inheritance 2 or more pairs of alleles are necessary for a given phenotypic expression. Colour of skin, hair and eyes are examples of polygenic inheritance. Multiple allele more than the normal 2 alleles are present at a locus in a chromosome within the population. Abo blood groups are examples of multiple alleles. Cumulative effect- (erroneously referred to as incomplete dominance) refers to the condition that hybrids are distinguishable from their parents, i. e. , red flowers (rr) x white flowers (rr) pink flowers (rr). In other words, the alternate forms of the alleles are neither dominant nor recessive; the phenotypic expression within a heterozygous offspring is a blend. Melanocytes specialized cells scattered among the cells of the epidermis that produce the main pigment (melanin) in human skin. The darker the skin the more melanin the persons melanocytes produce. 2 other pigments that influence skin: carotines (yellow), hemoglobin (red)
