However, hermites (which have many more) are also eukaryotes and it's very unlikely that a eukaryote evolved to prokaryote and then back into eukaryote in any evolutionary line. SAVE CANCEL. Exactly how many chromosomes we are talking about depends on the species. Birds are highly skilled, powerful flyers. Go. This picture of the human chromosomes lined up in pairs is called a karyotype. How many chromosomes does a robin have? The weight of evidence suggests that sex determination in birds is by a genic balance mechanism, in which the ratio of autosomes to Z chromosomes is the crucial factor. science math history literature technology health law business All Sections. Mutations can also cause an individual to have an abnormal number of chromosomes. Answers.com ® Categories Animal Life Birds Robins How many chromosomes does a robin have? In the chicken, this was found to be dependent on the expression of DMRT1. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Answer (1 of 3): As to what made them so large, there are many factors involved. The ZW sex-determination system is found in birds, some reptiles, and some insects and other organisms. A mosquito has 6 chromosomes, a pea plant has 14, a sunflower 34, a human being 46, and a dog 78. The other two chromosomes, X and Y, are the sex chromosomes. A sex chromosome, (also referred to as an allosome, heterotypical chromosome, or heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. already exists. For example, humans have a closer association to potatos than to hermites when you look at the chromosome count. Down syndrome or Trisomy 21 results from the presence of an additional chromosome on autosomal chromosome 21. The 22 autosomes are numbered by size. One is that larger animals take less time to heat up, and dinosaurs may have been partly exothermic. Another factor is that t-rex games likely hunted large prey so they needed to be large to take down their dinner. 80 Chromosomes and 40 sex cells. This type of mutation occurs during meiosis and causes cells to have either too many or not enough chromosomes. But other organisms, with genomes a thousand or even a million times larger than those of bacteria, divide their hereditary material among a number of different chromosomes. The ZW sex-determination system is reversed compared to the XY system: females have two different kinds of chromosomes (ZW), and males have two of the same kind of chromosomes (ZZ). In the interest of weight reduction, some avian bones have been fused or reduced in size, and many of the bones in a bird's body are hollow and filled with air (pneumatized). Flying, however, is an energetically costly activity, and there is hardly any aspect of avian anatomy that has not been influenced by the demands of flight.