Astronomers use light years to measure distances in space because space is so massive and distances so far that conventional numbering is inadequate and unmanageable. One light year is a distance measurement equivalent to six trillion miles.
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.
Laurentia<span> (</span>North American Craton<span>) is a large continental </span>craton<span> that forms the ancient geological core of the </span>North American<span> continent. Many times in its past, Laurentia has been a separate </span>continent<span> as it is now in the form of North America, although originally it also included the cratonic areas of </span>Greenland<span> and also the northwestern part of </span>Scotland, known as theHebridean Terrane<span>. During other times in its past, Laurentia has been part of larger continents and </span>supercontinents<span> and itself consists of many smaller </span>terranes<span> assembled on a network of Early </span>Proterozoic orogenic<span> belts. Small </span>microcontinents<span> and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable </span>Precambriancraton seen today.
