Homologous chromosomes are chromosome pairs, one from each parent, that are similar in length, gene position and centromere location.
Examples: X and Y chromosomes are homologous.
In Simple words any diploid organism (living being) contains two homologous chromosome pairs, one pair is inherited from father and other pair from mother, during the process of meiosis. These are same in length, genes and centromere position. A human has 22 pairs of homologous chromosomes (these do not include sex chromosomes).
Homologous pair of chromosomes at a glance:
- one maternal and one paternal
- carry same genes
- carry, same / different, alleles
- (usually) same / similar, length
- centromere in same position
- same banding pattern
- pair up in meiosis / form bivalent
Two similar chromosomes are called homologous chromosomes. The diploid organisms have two of each chromosomes, one inherited from the individual's father and one inherited from the individual's mother.
The two homologous chromosomes form an homologous pair. The homologous chromosome inherited from the individual's father and the homologous chromosome inherited from the individual's mother are not homologous chromosomes. Humans have 23 pairs of homologous chromosomes, hence, the somatic cells have 46 chromosomes arranged in 23 pairs.
Homologous chromosomes pair during meiosis and they do not pair during mitosis. During meiosis, the two chromosomes in each homologous pair align next to each other in a process called synapsis. The result of the synapsis process is a bivalent homologous pair or a tetrad. Since the homologous pairs align during Metaphase I, the gamete can reach to `2^23` possible combinations of chromosomes from the parent.
The chromosome error, or the extracopy of the chromosome 21 in each cell of the baby's body leads to Down Syndrome or trisomy. These errors are more likely in the eggs of older women, as the gene mutations are more likely in the sperm of older men.
"Homologous chromosomes are chromosome pairs, one from each parent, that are similar in length, gene position and centromere location."
basically they are chromosomes that are very similar in location and size, but they come from different alleles. This usually happens in the process go mitosis or meiosis.
Two similar chromosomes that have different alleles
A homologous pair is when a homologous sequence is separated by a gene duplication event, such as when a cell is going through mitosis, meiosis," homologous recombination, a retreotransposition event, aneuploidy, and replication slippage."
"If a gene in an organism is duplicated to occupy two different positions in the same genome, then the two copies are paralogous."
Essentially when there is two copies of the same gene within the same genome, but in different places, that is called a homologous pair.
homologous pairs are the chromosomes that contain the genes for the same thing but have different alleles, these chromosomes are usually paired together during mitosis