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