Chapter 12 The Chromosomal Basis Of Inheritance Flashcards
Today we know that genes are located on
Chromosomes
The chromosome theory of inheritance states
Mendelian genes have specific loci on chromosomes
Chromosomes undergo segregation and independent assortment
Morgan I’m the early 1900’s
Work provided evidence of a specific gene with a specific chromosomes
Noted wild type or normal phenotypes with alternate called mutant phenotypes
Concluded that eye color was related to the sex of the fly
Humans have two types of sex chromosomes
Larger X and smaller Y
The sry gene on the Y chromosome is required for testes
Ends of Y chromosome have regions that are homologous to corresponding regions of X chromosome
A gene that is located on either sec chromosome is called a
Sex-linked gene
For a recessive X linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
Linked genes
Genes located one the same chromosome that tend to be inherited together
Genetic recombination
The production of offspring with combinations of traits differing from either parent
Parental types
Offspring with a phenotype matching one of the parental phenotypes
Offspring with nonparental phenotypes are called
Recombinant types or recombinants
Genetic map
Ordered list of the genetic loci along a particular chromosome
Linkage map
Genetic map of a chromosome based on recombination frequencies
Distance between genes can be expressed as
Map units-one map unit represents a 1% recombination frequency
Cytogenetic maps
Indicate positions of genes with respect to chromosomal features
Non disjunction
Pairs of homologous chromosomes do not separate normally during Meiosis
As a result one gamete receives two of the same type of chromosome and another gamete receives no copy
Aneuploidy
Results from fertilization involving gametes in which non disjunction occurred
Offspring have an abnormal number of a particular chromosome
Monosomic
Trisomic
Zygote has only one copy of a particular chromosome
Zygote has three copies of a particular chromosome
Polyploidy
A condition in which an organism has more than two complete sets of chromosomes
Breakage of a chromosome can lead to four types of changes in chromosome structure
Deletion-removes a segment
Duplication-repeats a segment
Inversion-reverses orientation of a segment
Translocation-moves a segment from one chromosome to another
Down Syndrome
Aneuploid condition that results from three copies of chromosome 21
Klinefelter syndrome
Extra chromosome in a male producing XXY individuals
Turner syndrome
Produces X0 females who are sterile
