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Evolution of the Y Chromosome
Context:
A study on ape sex chromosomes reveals that only a small fraction of DNA sequences in the Y chromosome are similar to human counterparts.
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- Scientists found 14-27% of DNA sequences in ape Y chromosomes are similar to human Y chromosomes, indicating a faster rate of evolution.
- In contrast, over 90% of ape X chromosome sequences align with the human X chromosome is more stable and has remained relatively unchanged.
Key Highlights
- The Y chromosome, also known as the male sex chromosome, has been found to evolve rapidly compared to the stable X chromosome in both humans and apes.
- The team sequenced the sex chromosomes of six ape species.
- Including bonobo, chimpanzee, western lowland gorilla, Bornean orangutan, Sumatran orangutan, and siamang.
- Bornean and Sumatran orangutans diverged about 1 million years ago.
- Chimpanzee and bonobo diverged around 2.5 million years ago.
- Human lineage diverged from ape lineages roughly 7-20 million years ago.
- Including bonobo, chimpanzee, western lowland gorilla, Bornean orangutan, Sumatran orangutan, and siamang.
- Scientists used computational tools to identify chromosomal regions that remained relatively unchanged throughout evolution.
- Provides insights into evolutionary pressures on different genome parts.
- Sperm production requires more DNA replication than egg production, increasing the likelihood of mutations in the Y chromosome.
- Greater variation observed in Y chromosomes than X chromosomes among ape species.
- Example: Sumatran orangutan’s Y chromosome is twice as long as that of gibbons.
- 71-85% of Y chromosome and 62-66% of X chromosome lengths consist of repetitive elements.
- DNA palindromes, similar to word palindromes, can be over 100,000 letters long.
- The word “racecar” or “kayak” has a reversed sequence of letters, indicating a consistent forward and backward sequence.
- Contain genes and act as backup copies for damaged genes on the Y chromosome.
Implications for Conservation and Evolution:
- Understanding sex chromosome evolution aids in conservation of endangered non-human ape species.
- Offers insights into the broader mechanisms of human and ape evolutionary biology.
About
- The Y chromosome, or male sex chromosome, has undergone significant evolutionary changes.
- It is crucial for sexual development and fertility.
- Originated from an autosome (non-sex chromosome).
- Evolved through degeneration and gene loss.
- This process occurred independently in different animal and plant groups.
- Most original genes on the Y chromosome have been lost over time (Y chromosome degeneration).
- Lack of recombination and male-limited transmission contributed to this degeneration.
- Y chromosome is rich in repetitive DNA, including transposable elements and satellite DNA sequences.
- In plants like the white campion, the Y chromosome has evolved more slowly, retaining more functional genes.
- Evolutionary Forces:
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- Lack of recombination and male-limited transmission are key factors.
- Accumulation of deleterious mutations affects Y chromosome evolution.
- Unique evolutionary forces include the linkage of beneficial alleles with deleterious mutations, leading to the elimination of beneficial mutations.
