3. Basic Patterns of Human Inheritance Complex Inheritance and Human Heredity Section 1 Recessive Genetic Disorders  A recessive trait is expressed when the individual is homozygous recessive for the trait.

4. Complex Inheritance and Human Heredity Section 1 Table 11.2 Recessive Genetic Disorders in Humans

5. Complex Inheritance and Human Heredity Cystic Fibrosis  Affects the mucus-producing glands, digestive enzymes, and sweat glands  Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.  Without sufficient chloride ions in the cells, a thick mucus is secreted. Basic Patterns of Human Inheritance Section 1

6. Complex Inheritance and Human Heredity Albinism  Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes  White hair  Very pale skin  Pink pupils Basic Patterns of Human Inheritance Section 1

7. Complex Inheritance and Human Heredity Tay-Sachs Disease  Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides  Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration. Basic Patterns of Human Inheritance Section 1

8. Complex Inheritance and Human Heredity Galactosemia  Recessive genetic disorder characterized by the inability of the body to digest galactose. Basic Patterns of Human Inheritance Section 1

9. Complex Inheritance and Human Heredity Dominant Genetic Disorders  Huntington’s disease affects the nervous system.  Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short. Basic Patterns of Human Inheritance Section 1

10. Complex Inheritance and Human Heredity Basic Patterns of Human Inheritance Section 1

11. Complex Inheritance and Human Heredity Section 1

12. Complex Inheritance and Human Heredity Pedigrees  A diagram that traces the inheritance of a particular trait through several generations Basic Patterns of Human Inheritance Section 1

13. Complex Inheritance and Human Heredity Inferring Genotypes  Knowing physical traits can determine what genes an individual is most likely to have. Predicting Disorders  Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes. Basic Patterns of Human Inheritance Section 1

14. Complex Patterns of Inheritance Complex Inheritance and Human Heredity Incomplete Dominance  The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. Section 2

15. Complex Inheritance and Human Heredity Codominance  Both alleles are expressed in the heterozygous condition. Complex Patterns of Inheritance Section 2  Sickle-cell disease is one example.

16. Complex Inheritance and Human Heredity Sickle-cell Disease  Changes in hemoglobin cause red blood cells to change to a sickle shape.  People who are heterozygous for the trait have both normal and sickle-shaped cells. Sickle cell Normal red blood cell 7766x Complex Patterns of Inheritance Section 2

17. Complex Inheritance and Human Heredity Multiple Alleles  Blood groups in humans  ABO blood groups have three forms of alleles. Complex Patterns of Inheritance Section 2

18. Complex Inheritance and Human Heredity Coat Color of Rabbits  Multiple alleles can demonstrate a hierarchy of dominance.  In rabbits, four alleles code for coat color: C, c ch, c h, and c. Complex Patterns of Inheritance Section 2

19. Complex Inheritance and Human Heredity Epistasis  Variety is the result of one allele hiding the effects of another allele. Complex Patterns of Inheritance Section 2

20. Complex Inheritance and Human Heredity Sex Determination  Sex chromosomes determine an individual’s gender. Complex Patterns of Inheritance Section 2

21. Complex Inheritance and Human Heredity Dosage Compensation  The X chromosome carries a variety of genes that are necessary for the development of both females and males.  The Y chromosome mainly has genes that relate to the development of male characteristics.  In females, one X chromosome is inactivated in each cell. The inactivated X chromosome is visible in stained cells as a Barr body. Complex Patterns of Inheritance Section 2

22. Complex Inheritance and Human Heredity Sex-Linked Traits  Genes located on the X chromosome  Red-green color blindness  Hemophilia Complex Patterns of Inheritance Section 2 Sex-Linked Traits

23. Complex Inheritance and Human Heredity Polygenic Traits  Polygenic traits arise from the interaction of multiple pairs of genes. Complex Patterns of Inheritance Section 2

24. Complex Inheritance and Human Heredity Environmental Influences  Environmental factors influence an organism’s phenotype  Diet and exercise  Sunlight and water  Temperature Complex Patterns of Inheritance Section 2

25. Complex Inheritance and Human Heredity Twin Studies  Helps scientists separate genetic contributions from environmental contributions  Traits that appear frequently in identical twins are at least partially controlled by heredity.  Traits expressed differently in identical twins are strongly influenced by environment. Complex Patterns of Inheritance Section 2

26.  Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size. Chromosomes and Human Heredity Complex Inheritance and Human Heredity Karyotype Studies  Images of chromosomes stained during metaphase  Chromosomes are arranged in decreasing size to produce a micrograph. Section 3

27. Complex Inheritance and Human Heredity Telomeres  Telomere caps consist of DNA associated with proteins.  Serves a protective function for the structure of the chromosome Chromosomes and Human Heredity Section 3

28. Complex Inheritance and Human Heredity Nondisjunction  Cell division during which sister chromatids fail to separate properly  Down syndrome, also called trisomy 21 Chromosomes and Human Heredity Section 3

29. Complex Inheritance and Human Heredity Section 3