Explore the Introduction to Genetics (BIOL0003) module at University College London. Focused on the captivating realm of sex linkage and chromosome mapping, the document navigates through the intricacies of sex linkage, the chromosome theory, and two-point mapping. Unravel the mysteries behind the ...
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
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