Introduction to Genetics (BIOL0003) Notes - Sex Linkage and Chromosome Mapping

Sex Linkage and the Chromosome Theory
Sex Linkage and the Chromosome Theory
 Human chromosomes
o Genes are located on chromosomes
 Cell cycle
o Stages of the cell cycle
 Mitosis
 Chromosomes are visible
 G1
 Synthesis
 G2
o Measuring the amount of genetic material in a cell
 Shine ultraviolet light at the correct wavelength on the sample = absorbed by DNA
o Phases of mitosis
 Interphase
 DNA is not visible
 Prophase
 Chromosomes are visible
 Metaphase
 Chromosomes line up with centromeres in metaphase plate
 Anaphase
 Chromosomes pull apart to opposite ends of the cell
 Telophase
 Cell divides in 2
 Correspondence between genes and chromosomes




o
 Human chromosomes
 46 chromosomes – 2 copies of each chromosomes = 23 pairs
o One maternal copy + one paternal copy
 Sex chromosomes
o Do not come in pairs
 X (large) and Y (small) chromosomes – determines sex
o Women = XX
o Men = XY = hemizygous – big X and small Y
 Drosophila melanogaster – fruit fly
o Red and white eye
 Red eye = wild type mutant
 White eye = mutation removes the red mutant

, Sex Linkage and the Chromosome Theory
o Morgan’s reciprocal cross – used to test the role of parental sex on a given inheritance pattern
 1
 P1
o Red female x white male
 XXW x XY
 F1
o All females and males red




o
 F2
o All females red
o Half males red + half males white




o
 2
 P1
o White female x red male
 XWXW x XY
 F1
o All females red + all males white




o
 F2
o Half females red + half females white
o Half males red + half males white




o
o Morgan’s anomalous cross
 White females mated with red males – rarely gave all white females and red males
 Non-disjunction
o Females occasionally produced eggs with 2 X chromosomes or no X
chromosomes





o XWXWX – triploid = dies
o XWXWY – white female
o X0 – red male