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Pedigrees are typically used to track disease history
Diseases can be… Normal inheritance Recessive Dominant Sex-linked
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Autosomal vs. Sex-Linked
Autosomal traits are caused by genes on autosomes (chromosomes #1- #22) Sex-linked traits are caused by genes on the sex chromosomes (X or Y)
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Today we are learning sex-linked pedigrees
The sex-linked traits. You can find them here!
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Just a reminder… XY = MALE XX = FEMALE
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Key Point #4: For sex-linked diseases Males are either sick or healthy
Females can be sick, carrier, or healthy INM
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Let’s make a sex-linked pedigree for a family with some hemophiliacs
INM
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XHY XHXh Hemophilia XHXh XHY
The female offspring will ALL be carriers of the trait. The males will all be normal. Hemophilia in humans is due to an X- chromosome mutation. What will be the results of mating between a normal (non- carrier) female and a hemophiliac male? Xh Y XHXh XHY XH XHXh XHY XH
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Normal female (not a carrier) and sick man
Can you label their genotypes?
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Normal female (not a carrier) and sick man
Can you label all their genotypes? XhY XHXH Can you label their genotypes? XHY XHY XHY XHXh
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Okay, lets do one like this one more time…
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XhY XhXh Color Blindness XHXh XHY Xh Y XH Xh
The female offspring will either be carriers of the trait or color blind The males will either be normal or colorblind Color blindness in humans is due to an X-chromosome mutation. What will be the results of mating between a carrier female and a color blind male? Xh Y XHXh XHY XH XhXh XhY Xh
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Pedigree: Carrier female and a color blind male with 3 female & 1 male offspring
Based on what you know about the white-eyed female and red-eyed male fly. Can you create a Pedigree?
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REAL PROBLEM TIME… What if I only give you a pedigree and no parent genotypes to make a Punnett Square?
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STEP ONE: REMEMBER THE KEY!
Sick boy: Healthy boy: Healthy girl: Carrier girl: Sick girl:
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Phenotype Genotype Healthy female XHXH Carrier female XHXh Sick female
H=healthy h=sick Phenotype Genotype Healthy female XHXH Carrier female XHXh Sick female XhXh Healthy boy XHY Sick boy XhY
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Step 2: Find the sick males and label their genotypes
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Sex-linked recessive
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Sex-linked recessive XhY XhY
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Step 3: Find the healthy males and label their genotypes
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Sex-linked recessive XhY XhY
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XHY Sex-linked recessive XhY XhY
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Step 4: Find the sick girls and label their genotypes
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XHY Sex-linked recessive XhY XHY XhY
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Step 5: Find the healthy girls and decide if they are totally healthy or carriers! Make 2 punnett squares Look at the resulting offspring Circle the kids! Decide which mother genotype creates the correct offspring genotypes
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XHY Sex-linked recessive XhY XHY XhY
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Let’s start with the mom!
What do we know about her?
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Mom LET’S MAKE TWO PUNNETT SQUARES, LOOK AT THE BABIES
She’s a girl She’s either healthy or a healthy carrier She had babies with a healthy man She had 2 sick boys, 1 healthy boy, and a healthy or carrier girl LET’S MAKE TWO PUNNETT SQUARES, LOOK AT THE BABIES DETERMINE THE MOM’S GENOTYPE!
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Dad is def healthy! Mom is either healthy or a carrier!
XH Y XH Y XHXH XHY XHXH XHY XH XH Carrier Healthy XHXh XhY XHXH XHY Xh XH
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Let’s see if mom’s kids make sense if shes a carrier
XH Y HEALTHY GIRL, SICK BOY, HEALTHY BOY – OH MY!!!!! MAKES SENSE!!!!! XHXH XHY XH Carrier XHXh XhY Xh
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Let’s see if mom’s kids make sense if she’s healthy not carrier
XH Y HEALTHY GIRL, HEALTHY BOY – EEK!!! NO SICK BOY!!!!!! DOES NOT MAKE SENSE!!!!! NOT THE MOMMA XHXH XHY XH Healthy XHXH XHY XH
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HEALTHY GIRL, SICK BOY, HEALTHY BOY – OH MY!!!!!
XH Y HEALTHY GIRL, SICK BOY, HEALTHY BOY – OH MY!!!!! MAKES SENSE!!!!! XHXH XHY XH Carrier XHXh XhY Xh
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Mom, you are a carrier. XHY XHXh Sex-linked recessive XhY XHY XhY
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Only remaining mystery…
The daughter! Let’s look in the Punnett Square
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Daughter XHY XHXh XhY XH Y XHXH XH Xh She could be healthy OR
A carrier SHES SO MYSTERIOUS… XHXH XHY XH XHXh XhY Xh
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This is a sex linked trait. What can you conclude about daughter?
XHY XHXh Sex-linked recessive XhY XHY XhY XHXH or XHXh
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Whew! That was a lot of work for one problem…
That’s okay… they are difficult and YOU GOT IT RIGHT! Yay! Go you!
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Try this one…. (Remember you can use the reference sheet!)
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Rules for Sex Linked 1. More of one gender affected than the other , usually males 2. Females are usually carriers*, no male carriers for sex linked
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