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Understanding Mendelian Inheritance and Human Traits

This overview explores Mendelian inheritance, emphasizing the distinctions between homozygous dominant, homozygous recessive, and heterozygous phenotypes. It explains concepts such as intermediate inheritance and codominance, illustrated with examples like red, white, and pink flowers, as well as sickle cell anemia. The genetics of blood types is also detailed, highlighting multiple alleles. The use of pedigrees to trace traits in families is included, showcasing inheritance patterns and predicting genotypes for traits like attached and free earlobes, along with a brief discussion on recessive and dominant disorders.

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Understanding Mendelian Inheritance and Human Traits

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  1. Mendel and Human Traits

  2. Mendelian Inheritance • Heterozygous and Homozygous Dominant have the same phenotype • Homozygous recessive will have a different phenotype

  3. Intermediate Inheritance (Incomplete Inheritance) • The heterozygote is an intermediate of the two homozygotes • Red (RR) X White (WW) • Pink (RW) RR WW RW

  4. Pink Flower Ex. • RR - Red • WW - White • RW - Pink • All Offspring are pink R R W W

  5. Pink Flower Ex.(cont.) • RR - Red • WW - White • RW - Pink • 1/4 = Red • 1/2 = Pink • 1/4 = White R W R W

  6. Codominance • Sickle Cell Anemia • Blood cells are shaped like a sickle or half-moon • The sickled cells cause clots • Heterozygotes have some normal and some sickled cells • SS = Sickeled cells • RR = Regular cells • SR = Some regular, some sickled S S R R

  7. Sometimes there are more than two alleles for each trait Ex. Blood types A B O AB The alleles: A = IA B = IB O = i Multiple Alleles

  8. Multiple Alleles (cont.) • Blood type is determined by the surface proteins on a blood cell • Proteins are determined by what alleles the person has

  9. Multiple Alleles (cont.) A AB B O

  10. Multiple Alleles (cont.)

  11. Multiple Alleles (cont.) IA i • Can a man with type A blood and a woman with type AB blood have a daughter with type B blood? IA IA IA IB IA IB

  12. Inheritance in Humans

  13. Pedigrees • A family tree that records and traces traits in a family

  14. Gender • Gender • Males = Squares • Females = Circles • Relationship • A line connecting = marriage

  15. Relationships • Vertical lines = parents to children • Each row = one generation • Roman numerals (I,II,III, etc.) • Individuals (1,2,3,4, etc.) • Slash = death

  16. Phenotype • Shaded circle of square = A person who has the trait being studied • Unshaded = Does not have trait • Half-shaded = carrier or heterozygote

  17. Practice

  18. Answers Parents I 2 1 II Children/Siblings 2 1 3 Death

  19. Used to determine genotype Shaded = attached earlobes (recessive trait) Label the genotypes! F = free earlobes, f = attached earlobes

  20. Ff Ff Ff Ff F? ff F ? Ff F ? Used to determine genotype Shaded = attached earlobes (recessive trait) Label the genotypes! F = free earlobes, f = attached earlobes

  21. Ff Ff Ff Ff F? ff F ? Ff F ? Can predict offspring Genotype • What is the percent chance that the next child in generation III will have attached earlobes?

  22. Use a Punnett Square F f 25% chance for attached earlobes F f

  23. Diseases caused by recessive alleles • Cystic Fibrosis • Defect in cell membrane protein • Develop a thick mucus in lungs and digestive tract • Tay-Sachs • No enzyme that breaks down lipids • Lipids build up nervous tissue => Brain damage • Phenylketonuria (PKU) • No enzyme to change phenylalanine into tyrosine • Build up of phenylalanine => Brain Damage

  24. Dominant Allele diseases • Huntington’s Disease • Braek down of brain tissue • Achondroplasia • A form of dwarfism • Some forms of blindness

  25. Dominant Disorders • Most of the diseases caused by dominant alleles are lethal in Heterozygotes • The individuals die before they can reproduce • Low frequency of these alleles (<99.99%)

  26. Recessive Disorders • Recessive alleles are not lethal in heterozygotes • Will be passed on from generation to generation • Only homozygous recessive individuals are affected.

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