Homework: UP pages 46-50
Today in class we learned about X-Linkage (Sex Linkage) Problems. An X-linked trait is one whose gene is carried only on the X chromosome. Females have two X chromosomes (XX) and males have one (XY). There is no corresponding gene on the X chromosome, so one recessive trait could show up in a male. Examples are colorblindness, hemophilia, and Duchenne muscular dystrophy. Women who don't have the disease but have one recessive allele are called carriers.
Affected female has children with a normal male.
Steps 1&2: The first thing you do is assign letters and determine the genotypes of the parents. XA-normal, Xa=affected, and Y-male chromosome with no affected ellele.
XaXa-affected female, XAY-normal male
Step 3: Determine gamete genotypes prodeuced by each parent:
XaXa= Xa, Xa XAY= XA, y
For all X-linked punnett squares, always start with a normal punnett square and XY (male) on one side and XX (female) on the other
Step 4: Set up the punnett square with Xa and Xa on one side, and XA and y on the other
Step 5: Combine parental gametes: (the gametes from the F1 female should be XaXa)
Genotypes: 1/2 XAXa, 1/2 Xay (XaXa*XAy)
Phenotype: 1/2 normal female, 1/2 affected male
The word autosomal means any chromosome other than a sex chromosome.
We also learned about Pedigrees. Here is an example:
Squares=male
Circles=female
Black square/circle=affected individual
Half black/half white=carrier
In the first pair, the female is affected and the male is not. Their children aren't affected, but the female is a carrier. The carrier and her mate have 3 children, and 2 out of the 3 are affected. The ones that are affected have children, but the trait doesn'tshow up in them which means that they are carriers. The unaffected child of the 3 has an affected child, meaning she must have been a carrier.
Pedigrees can't be x-linked or not x-linked.
Next scriber-Gabriela
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