Here's the answer in picture form
<span>An incorrect number of
chromosomes is the most common form of genetic disorder that causes the fetus
to spontaneously abort. </span>The
human cells normally contain 23 pairs of chromosomes, for a total of 46
chromosomes in each cell. Error in one or more of the meiosis, mitosis,
maternal age, or environment are the possible cause of the chromosome
abnormalities. These abnormalities in the number chromosomes can cause problems
with development, growth and function of the body's systems. These changes can
occur in early fetal development, or in any cell after birth during the
formation of reproductive cells (sperm and eggs).
I) Locus- the chromosomal site where a specific gene is located. A locus is a fixed position on a chromosome, like the position of a gene or a marker. Each chromosome carries ,many genes; human's estimated haploid (n) protein coding genes are about 20,000, on the 23 different chromosomes.
ii) Interference; the observed double crossover frequency differs from the expected double crossover frequency. Cross over interference is used to refer to the non-random placement of crossovers with respect to each other during meiosis. It results in widely spaced crossovers along chromosomes. Interference may exert its effect across whole chromosomes. As chromosomes in many eukaryotes are large, interference must be able to act over megabase lengths of DNA.
iii) Linkage- the tendency for genes located in close proximity on the same chromosome to be inherited together. Normally when two genes are close together on the same chromosome, they do not assort independently and are said to be linked. Whereas genes located on different chromosomes assort independently and have a recombination frequency of 50%, linked genes have a recombination frequency that is less than 50%.
iv) Recombination- the process by which a new pattern of alleles on a chromosome is generated. Genetic recombination is the production of offspring with combinations f traits that differ from those found in either parent. During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. This may be followed by information transfer between the chromosomes.
<span>When a farmer stops cultivating farmland and abandons
it, the growth of wild grasses and weeds can be considered secondary succession
because of the presence of the existing soil. Secondary succession occurs in ecosystem
when soil have been disturbed or disrupted by humans such in a way of farming. Furthermore, the reason why it cannot be
categorize as primary succession because primary succession only occurs in
essentially lifeless areas, where soil is not capable of sustaining life. Specifically,
this is called old-field succession where wild grasses and weeds represents a new
plant species to colonize a bare soil after the farmer abandon the farmland.</span>
