determining sex females are xx, producing only x gametes. males are xy, producing both x & y...
TRANSCRIPT
Determining Sex
Females are XX, producing only X gametes. Males are XY, producing both X & Y gametes.
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Sex-linked Traits
Traits (genes) located on the sex chromosomes
Sex chromosomes are X and Y
XX genotype for femalesXY genotype for malesMany sex-linked traits carried on X chromosome
The X-Chromosome contains over 2300 genes
Most of these genes are unrelated to sex
Genes on X-Chromosome are expressed in both sexes
X-Chromosome has a centromere in the center of the chromosome
X-Chromosome
The Y-Chromosome contains around 25 genes
It is short & stubbyThe centromere is near the endMost important function is to
determine sex
Y-Chromosome
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Sex-linked Traits
Sex Chromosomes
XX chromosome - female Xy chromosome - male
fruit flyeye color
Example: Eye color in fruit flies
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Sex-linked Trait Problem
Example: Eye color in fruit flies (red-eyed male) x (white-eyed
female) XRY x XrXr
Remember: the Y chromosome in males does not carry traits.
RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female
XR
Xr Xr
Y
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Sex-linked Trait Solution:
XR Xr
Xr Y
XR Xr
Xr Y
50% red eyed female
50% white eyed male
XR
Xr Xr
Y
Red/Green ColorblindnessHemophiliaBaldnessMuscular Dystrophy
Some Sex-Linked Traits
Only females can be carriers
It is all or nothing for males
Notice the shape of Y-Chromosome
Sex-Linked Recessive Traits
http://www.dnai.org/d/index.html
Trait will show up in phenotype if in genotype
Sex-Linked Dominant Trait
Pedigrees
Another method used to study human heredity is a pedigree.
It is a a visual tool that is easier to follow.
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Female Carriers
A circle represents a female.
A square represents a male.
A horizontal line connecting a male and female represents a marriage.
A vertical line and a bracket connect the parents to their children.
A half-shaded circle or square indicates that a person is a carrier of the trait.
A completely shaded circle or square indicates that a person expresses the trait.
A circle or square that is not shaded indicates that a person does not express the trait but don’t know if they are carrier.
Section 14-1
Figure 14-3 A Pedigree
Tay-Sacs Pedigree
1. How many generations are there in this pedigree?
2. Who died in Generation 2?
3. How many kids were produced from generation 1?
Tay-Sacs Pedigree
4. Who got married in generation 3?
5. How many kids lived in generation 4?
What is Hemophilia?It is a blood clotting disorder.
Victims lack ONE of EIGHT proteins required for blood to clot.
Victims may die from cuts…or bruises!
It is a… …sex-linked trait!
