X-Linked Inheritance

Front 1

Hemizygous

Back 1

males are considered this in respect to sex chromosomes

Front 2

X inactivation

Back 2

lyon hypothesis, ‘lyonization’, one x cell is active, the other one is not (condensed ‘barr body’)

Front 3

4 characteristics of x-inactivation

Back 3

1. Random – maternal or paternal x is activate
2. Irreversible – barr bodies stay barr bodies
3. Clonally inherited – offspring of a cell inactivates the same chromosome
4. Females w/two distinct pop of cells.

Front 4

X-linked recessive characteristics

Back 4

- Incidence higher in males than females (might easily be only males – esp if the recessive one has super low fitness/is lethal)
- All affected males related through female relatives

Front 5

Female expression of x-linked recessives

Back 5

- Skewed x-linkage so that a higher percentage of the affected chromosomes are activated

Front 6

x-linked dominant characteristics

Back 6

- Males will have no sons and no unaffected daughters
- For some, females will get affected twice as much as males do, but will express the phenotype more mildly.