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Mendelian Exceptions

Explore Mendelian exceptions like incomplete dominance and codominance, as well as polygenic traits controlling characteristics like eye, skin, and hair color. Understand how multiple alleles influence traits such as blood types.

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Mendelian Exceptions

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  1. Mendelian Exceptions • Chapter 12 • Section 4

  2. Mendel’s Principles Revisited characteristics • Inheritance of biological _____________ is determined by individual units known as ______. • During sexual reproduction, genes are passed from parents to _________. • Two or more forms of the gene for a single _____ exist, some forms of the gene may be _________ and others may be recessive. genes offspring trait dominant

  3. Mendel’s Principles Revisited two • Organisms typically have ____copies of each gene, (one from each _______) • An organism’s _____ of genes (2 alleles) are segregated from each other when ________ are formed. • Alleles for different ______ usually segregate _____________ of one another. (through meiosis) • (Law of Independent Assortment) parent pair gametes genes independently

  4. Independent Assortment in Peas 9 __ Round yellow __ Round green __ Wrinkled yellow __ Wrinkled green 3 3 1

  5. 1.Incomplete Dominance • In incomplete dominance, neither allele is __________ so there is a blending of ______ when two different alleles for the same trait occur together. • Colors blend together • (______________ individuals = 3rd phenotype) dominant traits heterozygous red pink white

  6. Incomplete Dominance • In Four O’ Clocks, if you cross a red _____(which is always pure) with a white _____ (that is also always pure) , you get apink _____ (whichis always hybrid /heterozygous RR WW RW RW RW RW RW

  7. Incomplete Dominance • In another flower, if red ____ and blue ____ flowers are crossed, they produce a 3rd purple ____ flower • What would be the genotype ratio and phenotype ratio if you crossed two purple flowers? RR BB RB

  8. 2.Codominance alleles • Both _______ contribute to the phenotype of the organism by showing up simultaneously (at the same time) in heterozygous • individuals. • In cattle and horses, if you cross a pure ____ (RR) with a pure ______ (WW), you get (RW) which produces the color _____. red white roan

  9. Codominance • These cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third ___________. • If you cross a roan with a white… phenotype R W RW WW W roan white RW WW W roan white

  10. Codominance • Andalusian chickens also show this pattern of inheritance. • If you cross a black (BB) chicken • With a white (WW) chicken • You get black+white speckled (BW) chicken

  11. 3.Multiple Alleles • In this pattern of inheritance, the genes have more than _____ alleles controlling them and are therefore said to have multiple alleles. No individual has more than _____ alleles, but there are more than _____ possible alleles in a population, so a ______ will be expressed in more than two forms. two two two trait

  12. Multiple Alleles • Blood type in humans is an example of this inheritance pattern. • The ______ different blood groups: • A, B, O, and AB • Are produced by ______ different alleles: • A, B, and O four three

  13. Multiple Alleles • Examples of Blood type crosses

  14. Multiple Alleles • Blood Groups Antigen on Red Blood Cell Safe Transfusions Phenotype (Blood Type Genotype From To

  15. Multiple Alleles rabbit • The example of _______ hair color, which has at least four different alleles, is seen in these different Rex rabbits.

  16. 4. Polygenic Traits • Traits controlled by two or more genes • Show a wide range of phenotypes • The phenotype is produced by the interaction of more than ________ of genes. 1 pair

  17. Polygenic Traits polygenic many eye • These are called ___________ traits, which means “having _______ genes”. • In humans, _____ color, • _____ color, skin

  18. Polygenic Traits polygenic many eye • These are called ___________ traits, which means “having _______ genes”. • In humans, _____ color, • _____ color, • and _____ color skin hair

  19. Polygenic Traits polygenic many • These are called ___________ traits, which means “having _______ genes”. • In humans, _____ color, • _____ color, • and _____ color • are just a few of the many traits __________ by many genes. eye skin hair controlled

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