1. Sex-Linked Inheritance

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

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

4.  Autosome  Sex-linked chromosome  Locus/Loci

5.  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

7.  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

8.  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

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

10.  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

11.  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?

12.  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

13.  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

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

15. 13 14 48 37 23 21 18 In 50 words or less, summarize the key concepts from today's lesson. PROPERTY OF PIMA COUNTY JTED, 2010 15 50 Word Summary