Presentation on theme: "Chapter 7 Extending Mendelian Genetics. Basic Patterns of Human Inheritance Autosomal Recessive Genetic Disorders A recessive trait is expressed when."— Presentation transcript:
Chapter 7 Extending Mendelian Genetics
Basic Patterns of Human Inheritance Autosomal 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. Video
Albinism Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
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.
Cystic Fibrosis Punnett Square
Basic Patterns of Human Inheritance Autosomal Dominant Genetic Disorders Huntington’s disease affects the nervous system. Huntington’s disease Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short.
Huntington’s Disease Punnett Square
Pedigrees A diagram that traces the inheritance of a particular trait through several generations
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.
Sex chromosomes determine an individual’s gender Sex Determination
Sex-Linked Traits Genes located on the X chromosome Red-green color blindness Hemophilia Punnett Square
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.
X Chromosome Inactivation Tutorial
Epistasis Variety is the result of one allele hiding the effects of another allele. An epistatic gene can interfere with the expression of other genes. Albinism in mammals is caused by an epistatic gene that blocks the production of pigments.
Phenotype can depend on interactions of alleles. Complex Patterns of Inheritance
Incomplete Dominance The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.
Codominance Both alleles are expressed in the heterozygous condition. Sickle-cell disease is one example. People who are heterozygous for the trait have both normal and sickle-shaped cells.
Multiple Alleles Blood groups in humans ABO blood groups have three forms of alleles. Sometimes said to be codominant. Multiple alleles can demonstrate a hierarchy of dominance.
Polygenic Traits Polygenic traits arise from the interaction of multiple pairs of genes. Read pg. 206 in textbook.
Environmental Influences Environmental factors influence an organism’s phenotype Diet and exercise Sunlight and water Temperature
Gene Linkage Read pgs.209-211
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.
Is this a normal karyotype? Male or female?
Is this a normal karyotype? Male or Female?
Nondisjunction Cell division during which sister chromatids fail to separate properly Down syndrome, also called trisomy 21