Review Chromosomes 1-22 are Humans have 46 chromosomes (23 pairs). autosomes- “self-body” All traits we have discussed have been autosomal traits Males and females have an equal chance of inheriting autosomal traits F f F f FF Ff Ff ff Ex: Freckles: Autosomal Trait

Sex Chromosomes Last pair of chromosomes XX (homologous)= Female XY(non-homologous)= Male Sex-Linked Traits are traits coded by genes found on either the X or Y chromosome.

Boy or Girl? For any new offspring there is a 50/50 chance of producing a boy or a girl… X X Since the genes are on the X or Y; with sex linked traits sometimes whether or not a trait is inherited (good or bad) depends upon sex of the child X X X Y X Y

Sex-Linked Traits Referred to as being X- “linked” or Y- “linked” Normal traits: hormones 2nd sex characteristics Abnormal traits: hemophilia color blindness muscular dystrophy

X-linked Punnett Squares XR Xr XR Y XRXR XRXr Possible Genotypes: Female XRXR XRXr XrXr Male XR Y Xr Y XRY XrY 50% normal boy/girl 25% carrier girl 25% affected male (Assumes trait is recessive) Xr Xr XR Y XR XR Xr Y XRXr XRXr 100% girls carriers 100% boys affected (Assumes trait is recessive) XRXr XRXr 100% girls carriers 100% males normal (Assumes trait is recessive) XrY XrY XRY XRY

X-Linked Recessive Inheritance Passed from mothers to sons Always expressed in males Females are ‘carriers’ if heterozygous Genetic disorders like hemophilia muscular dystrophy color-blindness are all X-linked recessive

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H h h H h h h H h 50%/2:2 H h H 25% or 1:4 Sex male 50% or 2:2 All Male h h

Sex-Linked Traits and Pedigrees

MALE???

B R 25% B 0% B B B R 25% B R B B 50% BLACK R B R B R B B

Tracking Inherited Traits: Pedigrees Diagram used to visually determine patterns of inheritance. Tracks occurrence/frequency of genetic traits through generations of related organisms. Can be used to determine whether a gene is autosomal or sex-linked, and whether it is dominant or recessive. Can Track: Autosomal Dominant (RR, Rr) Autosomal Recessive (rr) X-Linked Recessive (XrXr, XrY) X-Linked Dominant (XRXR; XRXr) Y- Linked Dominant (XYR) Y-Linked Recessive (XYr)

What do you notice about this pedigree? Kate George

I II III IV ALBINISM: Inheritance? Key: Female Expressing Autosomal Recessive Key: Female Expressing Trait Male Heterozygous (If trait is recessive: “carrier”) Marriage P A S T G E N R I O I Children II Children are listed by birth order III Is II-7 affected? What sex is III-6? What are the genotypes of II-3 and II-4? How is albinism inherited? Yes IV F Heterozygous Present 

What do you notice about this pedigree? Aa Aa aa aa aa AA W What do you notice about this pedigree? Aa AA Aa Aa aa aa A_ A_ aa aa aa aa aa It represents an X-linked recessive inheritance

Autosomal recessive 4 4 Male parent for all future generations It is shaded because he is carrier for short-legged allele II-1 All 4 carry, 2 express

XBY XBXb XbY XBXb XB Y Xb Y XBX_ XBY Xb Xb XbY XbXb XBX_ XbY XBXb XbY XBXb XBY XBXb XBY XBY XbY XBY XBX_

I-1, II-2, II-3, II-7, III-3 DOMINANT 6 2 1 NIECE-UNCLE GRAMMA-GRANDSON

BOTH SIBLINGS EXPRESS. 50% CHANCE RECESSIVE PARENTS DO NOT EXPRESS, BUT, CHILDREN DO CONSANGUINE COUSINS IV-1, IV-3 I III-1, III-2 YES BOTH SIBLINGS EXPRESS. 50% CHANCE FEMALES X-LINKED RECESSIVE YES I DAD HAS RECESSIVE X YES

X-Linked traits are more commonly expressed by males. Why? Males inherit only 1 X chromosome, so the trait is expressed regardless of whether it is dominant or recessive