12.1 Basic Patterns of Human Inheritance

1. Chapter 12 12.1 Basic Patterns of Human Inheritance Recessive Genetic Disorders • A recessive trait is expressed when the individual is homozygous recessive for the trait.

2. Chapter 12 12.1 Basic Patterns of Human Inheritance 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.

3. Chapter 12 12.1 Basic Patterns of Human Inheritance 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

4. Chapter 12 12.1 Basic Patterns of Human Inheritance 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.

5. 12.1 Basic Patterns of Human Inheritance Galactosemia • Recessive genetic disorder characterized by the inability of the body to digest galactose.

6. Chapter 12 12.1 Basic Patterns of Human Inheritance 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.

7. Chapter 12 12.1 Basic Patterns of Human Inheritance

8. Chapter 12 12.1 Basic Patterns of Human Inheritance Pedigrees • A diagram that traces the inheritance of a particular trait through several generations

9. Chapter 12 12.1 Basic Patterns of Human Inheritance 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.

10. Chapter 12 12.2 Complex Patterns of Inheritance Incomplete Dominance • The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. (both alleles are blended)

11. Chapter 12 12.2 Complex Patterns of Inheritance Codominance • Both alleles are expressed in the heterozygous condition. (both alleles are seen at the same time)

12. Chapter 12 12.2 Complex Patterns of Inheritance Sickle-cell Disease Normal red blood cell • 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 7766x

13. Chapter 12 12.2 Complex Patterns of Inheritance Multiple Alleles • Blood groups in humans • ABO blood groups have three forms of alleles.

14. Chapter 12 12.2 Complex Patterns of Inheritance Coat Color of Rabbits • Multiple alleles can demonstrate a hierarchy of dominance. • In rabbits, four alleles code for coat color: C, cch, ch,and c.

15. Chapter 12 12.2 Complex Patterns of Inheritance Coat Color of Rabbits Chinchilla Albino Light gray Dark gray Himalayan

16. Chapter 12 12.2 Complex Patterns of Inheritance Epistasis • Variety is the result of one allele hiding the effects of another allele. eebb eeB_ E_bb E_B_ Dark pigment present in fur No dark pigment present in fur

17. Chapter 12 12.2 Complex Patterns of Inheritance Sex Determination • Sex chromosomesdetermine an individual’s gender.

18. Chapter 12 12.2 Complex Patterns of Inheritance Sex-Linked Traits • Genes located on the X chromosome • Red-green color blindness • Hemophilia

19. Chapter 12 12.2 Complex Patterns of Inheritance Polygenic Traits • Polygenic traits arise from the interaction of multiple pairs of genes.

20. Chapter 12 12.2 Complex Patterns of Inheritance Environmental Influences • Environmental factors • Diet and exercise • Sunlight and water • Temperature

21. Chapter 12 12.2 Complex Patterns of Inheritance 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.

22. Chapter 12 12.3 Chromosomes and Human Heredity Karyotype Studies • Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size. • Images of chromosomes stained during metaphase • Chromosomes are arranged in decreasing size to produce a micrograph.