Chapter 15 The Chromosomal Basis of Inheritance
Chromosome Theory of Inheritance - Mendelian genes have specific loci on chromosomes, and
it is the chromosomes that undergo segregation and independent assortment (Fig 15.1)
Genetic Terms
Wild Type - the normal (most common in natural populations) phenotype for a character
Mutant Phenotype - traits that are alternative to the wild type
Linkage
Sex-linked - genes located on a sex chromosome (Fig 15.3)
Linked genes - genes located on the same chromosome so that they are inherited together
in genetic crosses (Fig 15.4)
Recombination
Genetic recombination - the production of offspring with new combinations of traits
inherited from two parents (Fig 15.5)
Parental types - offspring that inherit a phenotype that matches one of the parental
phenotypes
Recombinants - offspring that have a different combination of phenotypes than either
parent
Genetic Mapping
Genetic map - an ordered list of the genetic loci along a particular chromosome (Fig 15.6)
Linkage map - a genetic map based on recombination frequencies (Fig 15.7)
Cytological map - a map which locate genes with respect to chromosomal features, such
as stained bands, which can be seen under the microscope
Some chromosomal systems of sex determination (Fig 15.8)
X-Y system
X-O system
Z-W system
Haplo-diploid system
The transmission of sex-linked recessive traits (Fig 15.9)
Sex-Linked Disorders
Duchenne muscular dystrophy
Hemophilia
X Inactivation - One X chromosome is inactivated during development, so there is only one copy
of the X chromosome active in any cell (Fig 15.10)
Barr body - the inactive X that has condensed into a compact object
Nondisjunction - the members of a pair of homologous chromosomes or sister chromatids do not
separate during meiosis (Fig 15.11)
Aneuploidy - an abnormal chromosome number
Trisomic - a chromosome is present in triplicate (Fig 15.14)
Monosomic - a chromosome is missing
Polyploidy - more than two complete chromosome sets
Alterations of chromosome structure (Fig 15.13)
Deletion
Duplication
Inversion
Translocation (Fig 15.x1)
Genomic imprinting – the parental effect on gene expression whereby identical alleles have
different effects on offspring, depending on whether they arrive in the zygote via the
ovum or via the sperm (Fig 15.15)
Prader-Willi/Angelman syndromes
Fragile X syndrome