A blood clot forms in a fibrous network of protein is called A) Fibrinogen.
Answer:
3. An even number of chromosomes are required for synapsis during prophase I and proper pairing during metaphase
Explanation:
Mules are hybrids of a cross between a female horse and a male donkey. Horses contain 64 chromosomes while donkeys contain 63 chromosomes in their somatic cells respectively. This means that they each produce 32 and 31 chromosomes respectively during meiosis. A mule, hence, contains 32+31= 63 chromosomes in their somatic cells.
This chromosome number in mules are uneven for meiosis to occur because meiotic division requires that an even number of homologous chromosomes pair together in a process called SYNAPSIS during prophase I of meiosis I. This is impossible in a mule because of the uneven number of chromosomes in its cells.
Also, during metaphase of meiosis, the homologous chromosomes need to be properly aligned at the equator for separation to occur. This is also impossible in a mule considering the number of chromosomes that don't add up.
Due to this reason of unevenness in the number of chromosomes present in a mule, meiosis will not occur and if meiosis (gamete formation) does not occur, reproduction cannot take place. Therefore, the mule is a sterile species i.e. cannot produce offsprings via sexual reproduction.
Answer:
The correct option is A. Steroid hormones exert their action by entering the nucleus of a cell and initiating or altering the expression of a gene.
Explanation:
Steroid hormones are derived from cholesterol and regulate multiple biological processes. All steroid hormones exert their action by crossing the plasma membrane and by binding with their respective intracellular receptors. They stimulate cell growth in a very different way, their lipophilic nature gives them the ability to cross lipid barriers, so, without the need for extracellular signals, these hormones can easily enter the cell, cross the cytoplasm and reach the nucleus. There they bind to specific receptors that are associated with DNA promoter regions, modifying their structure and promoting the expression of the genes under their control.
2, 4, 1, 3, 5
the tiles go into the sequence in that order.
first one is tile 2, second is tile 4, etc.
