Yes, it is possible for a human to have 44 chromosomes, although extremely rare. This typically occurs due to a specific type of chromosomal rearrangement called a Robertsonian translocation.
Understanding Chromosomes and Translocations
Humans usually have 46 chromosomes: 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes (XX for females, XY for males). A Robertsonian translocation involves the fusion of two acrocentric chromosomes (chromosomes with the centromere near one end). When this happens, the individual has one less chromosome pair, resulting in 45 chromosomes. However, if two parents both carry the same balanced Robertsonian translocation, they can have a child with 44 chromosomes – inheriting one copy of the fused chromosome from each parent.
Several sources confirm the existence of individuals with 44 chromosomes, though they are exceptionally rare. These individuals may appear phenotypically normal, as highlighted in reports such as the case of a phenotypically normal fetus with 44 chromosomes and homozygous 14;21 translocations https://pubmed.ncbi.nlm.nih.gov/7173858/. A man from China with 44 chromosomes is also mentioned in several sources https://www.kqed.org/quest/5239/and-then-there-were-44, https://www.thetech.org/ask-a-geneticist/articles/2013/48-46/.
Implications and Frequency
The rarity of individuals with 44 chromosomes is emphasized across multiple sources. For example, the possibility of a new human subspecies with 44 chromosomes is considered exceptionally rare https://dnascience.plos.org/2016/01/21/can-a-quirky-chromosome-create-a-second-human-species/. The likelihood of two parents carrying the same balanced translocation is low, contributing to the infrequency of this chromosomal configuration in offspring.
While individuals with 44 chromosomes can exist and may appear healthy, this condition remains exceedingly uncommon. Their ability to produce viable offspring is also a factor that would influence the spread of this chromosomal number in the population.
