A human with 44 chromosomes is possible, but it's not the typical human chromosomal number. This can result from a specific type of chromosomal rearrangement.
Understanding Human Chromosomes
Normally, humans have 46 chromosomes: 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes (XX for females, XY for males). The autosomes carry the majority of our genetic information dictating physical characteristics and bodily functions. Sex chromosomes determine sex.
The 44 Chromosome Scenario
Individuals with 44 chromosomes typically possess this reduced number due to a Robertsonian translocation. This is a type of chromosomal abnormality where two acrocentric chromosomes (chromosomes with the centromere near one end) fuse together. This fusion results in one less chromosome pair.
- Robertsonian Translocations: These translocations involve the loss of chromosomal material at the fusion point but may be symptom-free depending on the chromosomes involved.
- Documented Cases: There are documented cases of individuals with 44 chromosomes who are phenotypically normal, meaning they don't exhibit obvious physical or health problems. [Source: There are symptom-free people running around with 44 chromosomes who got to this number in this exact way.16-Jan-2013] [Source: The most recent is a man from China… 16-Jan-2013]
- Reproductive Challenges: While some individuals with 44 chromosomes are healthy, they may experience fertility issues. Producing viable offspring with a partner who has the standard 46 chromosomes may be difficult or impossible. [Source: If a male with 44 chromosomes wants to have children with a female with 46 chromosomes, this will not work. He won't be able to have viable offspring.]
- Homozygous Translocations: In some rare instances, a fetus has inherited two copies of a Robertsonian translocation, resulting in 44 chromosomes. While some may appear phenotypically normal at birth, long-term neurodevelopmental outcomes are unknown. [Source: ...human fetus with 44 chromosomes with homozygous 14;21 translocations. This fetus appeared phenotypically normal but the long-term neurodevelopmental outcome had… ]
Evolutionary Context
The reduction in human chromosome number from a hypothesized ancestral 48 to the current 46 is also believed to have occurred through Robertsonian translocations over a very long period of evolution. [Source: The story of how this patient ended up with 44 chromosomes mirrored my story of how humans may have gone from 48 to 46 chromosomes a million or so years ago.]
Conclusion
Having 44 chromosomes is possible, resulting from chromosomal rearrangements such as Robertsonian translocations. While some individuals with this condition appear healthy, fertility issues and potential long-term health concerns are factors to consider.
