1. Sex-Linked Traits

2.
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3. Karyotype Studies (not being tested on)
Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size
Images of chromosomes stained during metaphase
Chromosomes are arranged in decreasing size to produce a micrograph

5. Telomeres Telomere caps consist of DNA associated with proteins
Serves a protective function for the structure of the chromosome
They might also be involved in aging and cancer

7. Nondisjunction (not being tested on)
Cell division during which sister chromatids fail to separate properly
If this occurs during Meiosis I or II then the resulting gametes will not have the correct number of chromosomes
Down syndrome: nondisjunction occurred on chromosome 21.
The result is short stature, heart defects, and mental disability

8. Chromosome Inactivation
Barr bodies: the inactivated X chromosome in females
One X chromosome is randomly inactivated in an early embryonic cell
Example: Tortoise shell cats
The gene for coat color is on the X chromosome.
When the cat is heterozygous in coat color (black/orange) it is born with patches of different colored fur on its body.

10. Sex-Linked Traits
Traits are controlled by genes located on the sex chromosomes
Humans: 22 homologous pairs of matching chromosomes called autosomes, and one pair of sex chromosomes (XX or XY)
There are genes found on the X chromosome that are not found on the Y chromosome
Inheritance of traits determined by these genes is therefore linked to the sex of the individual

11. X-linked Traits Genes located on the X chromosome that control traits
Since males have only 1 X chromosome they are affected by recessive X-linked traits
Females are less likely to express a recessive trait because she has two X chromosomes. One of the X chromosomes can mask the affect of the trait.

12. Sex Determination Sex chromosomes determine an individual’s gender
Autosomes are all the other chromosomes that determine everything else. (i.e. Body cells)
The Y chromosome determines the sex of the organism
XX=Female; XY=Male

13. When completing crosses…
When writing genotypes:
Put the trait as a superscript to the sex chromosome
XRXR; XRY
Capital letter represents a dominant allele and lowercase letter represents a recessive allele

14. Examples (to name a few)
Red-Green Color Blindness
Hemophilia

15. Ex: Hemophilia
Recessive sex-linked disorder characterized by delayed clotting of the blood.
Very rare in females because she would need to have both X chromosomes with the recessive trait.

16. Types of Genotypes XHXH (female with normal blood clotting)
XHXh (female with normal blood clotting, but is a carrier of the trait)
XhXh (female with hemophilia)
XHY (male with normal blood clotting)
XhY (male with hemophilia)

18. Ex: Red-Green Color Blindness
This is a recessive X-linked trait. A male only needs one copy of this allele in order to be colorblind
A female would need to have two copies of the recessive allele. Thus it is very rare to find a color blind female