Sex-Linked Inheritance

 Genetically, what determines whether a fetus is a boy or girl?  Who determines gender, Mom or Dad? Explain.

 Explain how gender is determined  Explain why sex-linked traits are more common in males than in females

 Autosome  Sex-linked chromosome  Locus/Loci

 Humans have 23 pairs of chromosomes  1-22 chromosome pairs ◦ are autosomal chromosomes (autosomes) ◦ chromosomes not related to gender  23 rd chromosome pair are the sex chromosomes ◦ XX = female ◦ XY = male

 Most X-linked genes ◦ have no homologous loci (positions) on Y  Very few genes found on the Y chromosome ◦ most genes on the Y chromosome associated with maleness (e.g. testes determining factor)  More than 100 have now been mapped

 Father determines gender  Donates Y chromosome to sons  Donates X chromosome to daughters  Fathers cannot pass sex-linked traits to son because  He doesn’t give them an X chromosome  Males receive X chromosome from mother  So the mother passes sex-linked traits to son

 Pass sex-linked alleles (X) to both daughters and sons

 Females have fewer sex-linked disorders because ◦ It only shows up if homozygous recessive ◦ Females have two X chromosomes ◦ more often carriers of recessive allele  Males have only one X chromosome ◦ If they have one disorder allele they have the disorder ◦ more common to have sex-linked disorders

 Red-green colorblindness is a sex-linked trait.  The dominant allele, C, produces normal color vision  The recessive allele, c, produces red-green color blindness.’  If a man with normal color vision marries a color-blind woman, what is the chance of their having a color-blind son?  A color-blind daughter?

 Color blindness ◦ most commonly red-green color blindness ◦ X-linked recessive disorder ◦ Individuals with this color blindness see fewer than 25 colors ◦ Results from some or all of the receptors that respond to red and green being weakened or absent

 Hemophilia A ◦ Causes lack of blood clotting ◦ X-linked recessive disorder ◦ Symptoms  tend to bruise easily  internal bleeding can cause problems with muscles and joints

 Duchenne Muscular Dystrophy ◦ disease that results in the progressive weakening of skeletal muscle ◦ X-linked recessive disorder

In 50 words or less, summarize the key concepts from today's lesson. PROPERTY OF PIMA COUNTY JTED, Word Summary