Sex-linked Traits

Sex-linked traits are traits that are found on the sex chromosomes (23rd pair), most commonly on the X chromosome.

When working with sex-linked traits you have to use the X and Y chromosome with the alleles written as superscript.

Sex-linked traits are typically recessive and are seen more predominantly in males as they only have to inherit one allele in order to express the trait.

Colorblindness is a recessive, x-linked trait. This punnett square shows a colorblind female crossed with a normal-vision male. There is no allele on the Y chromosome in this punnett square because the trait is only found on the X chromosome.

(XX= female, XY= male)

color blind female x normal vision male

Can you see the numbers in these color blind tests?

Concept Check...

Hemophilia is a recessive, sex-linked disorder that prevents the blood from clotting properly resulting in excessive bleeding.

Create a punnett square to cross a heterozygous female with a unaffected male. What is the probability that they will have a child who has hemophilia? (answer is at the bottom of page)

Watch the video and add to your notes.

Fruit Fly Genetics Lab

Click the lab and follow the instructions to create two generations of fruit flies. Answer the following questions on a piece of paper:

Did you select red or white eyed flies for your first cross? __________ male ____________ female
What were the phenotypes of your F1?
Did you select red or white eyed flies for your second cross? __________ male ____________ female
What were the phenotypes of your F2?
Do a punnett square to determine the genotypes of your second cross.
- What were the genotypes of the F2? ___________ ___________ ___________ ___________
- What would the genotypes of the parents of that cross have to be (the two F1 that you crossed)? ____________ _____________

Answer to your concept check...

Inheritance Quizlet

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