The Chromosomal Basis of Inheritance: Chp 15 Flashcards
chromosome theory of inheritance
states that genes have specific locations on chromosomes and that it is chromosomes that segragate and assort independently
sex-linked gene
located on a sex chromosome
duchenne muscular dystrophy
an x-linked disorder characterized by a progressive weakening of the muscles and loss of coordination
hemophilia
an x-linked disorder characterized by having blood with an inability to clot normally, caused by the absence of proteins required for blood clotting
x inactivation
regulates gene dosage in females. although female mammals inherit two x chromosomes, one of the x chromosomes in each cell of the body becomes inactivated during embryonic development by methylation. as a result, males and females have the same effective dose of genes with loci on the X chromosome
barr body
when the inactive chromosomes condense and lies along the inside of the nuclear envelope
linked genes
located on the same chromosome and therefore tend to be inherited together during cell division
genetic recombination
the product of offspring with a new combination of genes inherited from the parents. many genetic crosses yield some offspring with the same phenotype as one of hte parents and some offspring with phenotypes different from either parent
linkage map
a genetic map that is based on the percentage of crossover events
map unit
equal to a 1% recombination frequency. map units are used to express relative distances along the chromosome
nondisjunction
occurs when the members of a pair of homologous chromosomes do not separate properly during meiosis 1, or sister chromatids don’t separate properly during meiosis 2
aneuploidy
if the offsping has an incorrect chromosome number as a result of disjunction
trisomatic
fertilized eggs that have received three copies of the chromosome
monosomic
fertilized egg that has received just one copy of a chromosome
polyploidy
the condition of having more than two complete sets of chromosomes, forming a 3n or 4n individual.
deletion
occurs when a chromosomal fragment is lost, resulting in a chromosome with missing genes
duplication
occurs when a chromosomal segment is repeated
inversion
occurs when a chromosomal fragment breaks off and reattaches to its original position-but backwards
translocation
occurs when the deleted chromosome fragment joins a nonhomologous chromosome
down syndrome
an aneuploid condition that is the result of having an extra chromosome 21
klinefelter syndrome
an aneuploid condition in which males possess the sex chromosomes XXY causing them to have male sex organs but are sterile
turner syndrome
a monosomic condition in which the female has just one sex chromosome, an X
genoic imprinting
the phenotypic effect of a gene may depend on which allele is inherited from each parent
