Studied by 3 people
Loci
plural form of locus (positions)
Morgan’s experiments:
he noted wild-type (normal) phenotypes that were common in the fly populations
Traits alternative to the wild type are called mutant phenotypes
Chromosomal Basics of Gender
humans (and other mammals) have 2 types of sex chromosomes: X and Y (all other chromosomes are autosomes)
two X chromosomes associated w/ female anatomy
One X and one Y chromosome associated w/ male anatomy
Crossing can happen in males
ends of the Y chromosome have regions that are homologous w/ corresponding regions of X chromosome so they can pair and behave like homologs during meiosis in males
Sex- linked inheritance
a gene that is located on either sex chromosome is called a sex-linked gene— either X-linked or Y-linked
many y- linked genes help determine male gender
X- chromosome have genes for many other traits
For a recessive X lined trait to be expressed:
females need 2 copies of the allele (homozygous)
Males need only 1 copy of the allele (hemizygous)
Ex. Color blindness and hemophilia
X inactivation in female mammals
In mammalian females, one of the two X chromosomes is randomly inactivated during embryonic development which condenses into a Barr body
Abnormal chromosome number
nondisjunction occurs when pairs of homologous chromosomes (or sister chromatids) do not separate normally during meiosis I or II
As a result, 1 gamete receives 2 of the same type of chromosome, and another gamete receives no copy
Aneuploidy
Fertilization after no disjunction results in aneuploidy (abnormal number of chromosomes)
Polyploid
a condition in which an organism has more than two complete sets of chromosomes
Triploidy (3n) is three sets of chromosomes
Tetraploidy (4n) is four sets of chromosomes
Only common in plants
Pedigrees
Family tree that contains a family’s history for a particular trait across generations
