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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. - PowerPoint PPT Presentation
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12.1 Basic Patterns of Human Inheritance
Chapter 12
Recessive Genetic Disorders
A recessive trait is expressed when the individual is homozygous recessive for the trait.
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.
12.1 Basic Patterns of Human Inheritance
Chapter 12
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
12.1 Basic Patterns of Human Inheritance
Chapter 12
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
Chapter 12
Galactosemia
Recessive genetic disorder characterized by the inability of the body to digest galactose.
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.
12.1 Basic Patterns of Human Inheritance
Chapter 12
12.1 Basic Patterns of Human Inheritance
Chapter 12
Pedigrees
A diagram that traces the inheritance of a particular trait through several generations
12.1 Basic Patterns of Human Inheritance
Chapter 12
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.
12.1 Basic Patterns of Human Inheritance
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
Codominance
Both alleles are expressed in the heterozygous condition. (both alleles are seen at the same time)
12.2 Complex Patterns of Inheritance
Chapter 12
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
12.2 Complex Patterns of Inheritance
Chapter 12
Multiple Alleles
Blood groups in humans
ABO blood groups have three forms of alleles.
12.2 Complex Patterns of Inheritance
Chapter 12
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.
12.2 Complex Patterns of Inheritance
Chapter 12
Coat Color of Rabbits
Light gray
Dark gray Himalayan
Albino
Chinchilla
12.2 Complex Patterns of Inheritance
Chapter 12
Epistasis
Variety is the result of one allele hiding the effects of another allele.
No dark pigment present in fur Dark pigment present in fur
eebbeeB_ E_bb E_B_
12.2 Complex Patterns of Inheritance
Chapter 12
Sex Determination
Sex chromosomes determine an individual’s gender.
12.2 Complex Patterns of Inheritance
Chapter 12
Sex-Linked Traits
Genes located on the X chromosome
Red-green color blindness
Hemophilia
12.2 Complex Patterns of Inheritance
Chapter 12
Polygenic Traits
Polygenic traits arise from the interaction of multiple pairs of genes.
12.2 Complex Patterns of Inheritance
Chapter 12
Environmental Influences
Environmental factors
Diet and exercise
Sunlight and water
Temperature
12.2 Complex Patterns of Inheritance
Chapter 12
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.
12.2 Complex Patterns of Inheritance
Chapter 12
Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
12.3 Chromosomes and Human Heredity
Karyotype Studies
Images of chromosomes stained during metaphase
Chromosomes are arranged in decreasing size to produce a micrograph.
Chapter 12
