• Reciprocol crosses
• Phenotype tree

Tips

• Write down alleles
• Genotype of parents
• Phenotype of parents
• Gametes (haploid)

Y-Chromosome has 1/3 genetic material as x-chromosome.

Sex-linked genes don't matter if dominant or recessive if person only has 1 copy of the gene.

Male

Transmits X to all daughters.

Transmits Y to all sons.

Female

Can be carriers of recessive alleles

Transmits 1 X randomly to son or daughter.

X-Linked Recessive

(XLR)

• Disproportionaly affects males
• Traits appear dominant in males
• Traits appear recessive in females - more often carriers.

• Red/green colorblindness

• Hemophilia

• Fragile-X Syndrome

Pedigrees

• Male = square
• Female = circle

X-Linked Dominant

(XLD)

• Phenotype is observed in heterozygous females
• Affected males produce all affected daughters, but not affected sons.
• Disproportiontly affects females

• Rickets

Y-Traits

Appear only in males

• Every male affects every offspring male (but not if cheating parents) : > Hearing loss

X-Dosage Compensation

Females - in each cell - 1 x is inactive

Barr Body

Condensed X = inactive X

Males do not have a barr body.

X-Inactivation

Occurs in females at 15 days gestation.

• Mosaic of which X is active and which is inactive.
• Affects severity of dominant X
• Complicates XLR genes.