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.

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.

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

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.

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

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.

Chapter 12
12.1 Basic Patterns of Human Inheritance

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

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.

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)

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)

Chapter 12
12.2 Complex Patterns of Inheritance
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

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

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 , c ch
, c h
, and c .

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

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

Chapter 12
12.2 Complex Patterns of Inheritance
Sex Determination
 Sex chromosomes determine an individual’s gender.

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

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

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

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.

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.