Gametes are haploid cells which means they have only half the normal number of somatic cell (diploid). Somatic cells have 46 chromasomes, organised into 23 pairs, and gametes have only one chromasome from each pair.
23
Gametes (eggs and sperm) need to have half the normal chromosome number OS that when they combine the create a normal (or diploid) cell with 46 chromosomes.
A human gamete has 22 autosomes and one sex chromosome. However, special cases may arise due to aneuploidy which can result in two copies of an autosome, e.g. chromosome 21, 18, etc. or the non-disjunction of sex chromosomes, X and/or Y.
2 coiled DNA molecules.
Meiosis creates gametes (sperm and ova/eggs) which are involved in sexual reproduction. The result of meiosis is cells with half the number of chromosomes as a somatic (non-sex) cell. This ensures that when the gametes join during sexual reproduction, the resulting organism has the correct number of chromosomes (half from each gamete). Thus meiosis maintains the chromosome number.
in S phase
The chromosome number only doubles when two haploid gametes form to produce a diploid zygote. Example: In humans, sperm cells and eggs have 23 chromosomes, the haploid number. Once they fuse, the number doubles to 46 chromosomes. You may be confusing this with chromosome replication. In chromosome replication, the number of chromosomes does not double, but the number of strands double. (A single stranded chromosome turns into a double stranded chromosome.) However, it is still considered a single chromosome, but with identical sister chromatids. This replication occurs during the S-phase of the cell cycle, before mitosis or meiosis.
its good
There are two chromatids for each chromosome before the S-phase. The S-phase is wherein DNA of each chromosome is replicated.
23
Have to say Nay. Two chromosomes are 'homologous' , to my understanding, only if each is IDENTICAL with the other - this means a pair. Gametes are haploid, meaning that only one copy of each (normally diploid or paired) chromosome (s) is (are) present.
Have to say Nay. Two chromosomes are 'homologous' , to my understanding, only if each is IDENTICAL with the other - this means a pair. Gametes are haploid, meaning that only one copy of each (normally diploid or paired) chromosome (s) is (are) present.
A human gamete has 22 autosomes and one sex chromosome. However, special cases may arise due to aneuploidy which can result in two copies of an autosome, e.g. chromosome 21, 18, etc. or the non-disjunction of sex chromosomes, X and/or Y.
S phase is complete when each chromosome has been duplicated.
Two, one from each parent. Over 90,000 genes are found on each chromosome and are mostly responsible for protein productions.
2 coiled DNA molecules.
usually by their 40's or 50's
Every human being has 23 pairs of chromosome which translates into 46 chromosomes.
Meiosis creates gametes (sperm and ova/eggs) which are involved in sexual reproduction. The result of meiosis is cells with half the number of chromosomes as a somatic (non-sex) cell. This ensures that when the gametes join during sexual reproduction, the resulting organism has the correct number of chromosomes (half from each gamete). Thus meiosis maintains the chromosome number.