Chapter 7 Extending Mendelian Genetics
Feb 24, 2016
Chapter 7Extending Mendelian Genetics
Basic Patterns of Human Inheritance
Autosomal Recessive Genetic DisordersA 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.
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 HemophiliaPunnett 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.
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 exerciseSunlight and waterTemperature
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?
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