Below are three statements. classify them as examples of independent orientation, crossing over, or random fertilization. i: the formation of a zygote from an egg and a sperm is an unpredictable event. ii: random combinations of paternal and maternal chromosomes end up in gametes. iii: an allele on the paternal chromosome 18 ends up on the maternal chromosome 18

I) Random Fertilization

II) Independent Orientation

III) Crossing-over

Explanation:

I) Fertilization is a phenomenon that occurs in sexually-reproducing organisms only. It is the process whereby the male gamete (sperm cell) fuses with the female gamete (egg cell) to produce a ZYGOTE. Both sperm and egg cells are usually haploid in chromosomal number. The sperm randomly fertilizes the egg. This process is described as unpredictable in the question because, no one knows which sperm will fertilize which egg. It occurs by chance.

II) During Metaphase I of the meiotic process, homologous chromosomes from maternal and paternal parent aligns at the equator of the cell in a random orientation. This random orientation determines which maternal or paternal chromosome ends up in which cell. According to the law of independent assortment, each gamete will randomly contain one allele of each gene. Note that, each of the two alleles of a gene comes from each parent. Hence, based on the example, the combination of maternal and paternal chromosomes that are present in each gamete occurs randomly during the orientation in Metaphase I of meiosis.

III) Crossing-over also called Recombination is a unique process that occurs only during meiosis. It occurs during the Prophase stage of meiosis specifically. It involves the exchange of chromosomal segment between non-sister chromatids of homologous chromosomes ( similar but non-identical chromosomes from each parent). In the example given in the question, the chromosome involved is Chromosome 18. The homologous chromosomes from each parent (male and female) lie side by side to form a TETRAD structure during prophase, after which a chromosomal segment containing alleles is exchanged between non-sister chromatids of maternal and paternal chromosome 18.

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