Rucete ✏ Biology In a Nutshell
1. Sex Chromosomes vs. Autosomes
- Sex chromosomes: Determine an individual’s sex
- Humans: X and Y chromosomes
- Females: XX
- Males: XY
- Autosomes: All other non-sex chromosomes (22 pairs in humans)
2. Sex-Linked Inheritance
- Refers to genes located on the sex chromosomes, especially the X chromosome
- X-linked traits are more common because the X chromosome carries more genes than the Y chromosome
- Males are more likely to express X-linked recessive traits since they have only one X chromosome
Examples of X-linked disorders:
- Hemophilia
- Muscular dystrophy
3. X Inactivation
- In female mammals, one of the two X chromosomes is randomly inactivated in each cell
- The inactivated X becomes a dense body called a Barr body
- This balances gene expression between males (XY) and females (XX)
Example: Calico Cats
- Female calico cats display patches of different fur colors due to X-inactivation of different alleles in various cells
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Biology in a nutshell