The medulla oblagonta. Its main function is to send signals to the muscles that control respiration to cause breathing to occur.
Answer:
The delivery of the paternal genome to the egg is a primary goal of fertilization. In preparation for this step, the nucleus of the developing spermatozoon undergoes extensive morphological and biochemical transformations during spermatogenesis to yield a tightly compacted sperm nucleus. These modifications are essentially reversed during fertilization. As a result, the incorporated sperm nucleus undergoes many steps in the egg cytoplasm as it develops into a male pronucleus. The sperm nucleus (1) loses its nuclear envelope, (2) undergoes nucleoprotein remodeling, (3) decondenses and increases in size, (4) becomes more spherical, (5) acquires a new nuclear envelope, and (6) becomes functionally competent to synthesize DNA and RNA. These changes are coordinate with meiotic processing of the maternal chromatin, and often result in behaviors asynchronous with the maternal chromatin. For example, in eggs fertilized during meiosis, the sperm nucleus decondenses while the maternal chromatin remains condensed. A model is presented that suggests some reasons why this puzzling behavior exists. Defects in any of the processes attending male pronuclear development often result in infertility. New assisted reproductive technologies have been developed that ensure delivery of the sperm nucleus to the egg cytoplasm so that a healthy embryo is produced. An emerging challenge is to further characterize the molecular mechanisms that control sperm nuclear transformations and link these to causes of human infertility. Further understanding of this basic process promises to revolutionize our understanding of the mystery of the beginning of new life.
Explanation:
The delivery of the paternal genome to the egg is a primary goal of fertilization. In preparation for this step, the nucleus of the developing spermatozoon undergoes extensive morphological and biochemical transformations during spermatogenesis to yield a tightly compacted sperm nucleus. These modifications are essentially reversed during fertilization. As a result, the incorporated sperm nucleus undergoes many steps in the egg cytoplasm as it develops into a male pronucleus.
The correct option is (D) Nucleotide variability and average heterozygosity
The higher the proportion of loci that are "fixed" in a population, the lower are that population's nucleotide variability and average heterozygosity.
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What does it indicate when a gene in a population is fixed?</h3>
- In population genetics, fixation is the transformation of a gene pool from one in which at least two alleles of a certain gene exist in a given population to one in which only one allele persists.
- Any allele must eventually be lost entirely from the population or fixed (permanently established at 100% frequency in the population) in the absence of mutation or the heterozygote advantage.
- Selection coefficients and random variations in allelic proportions determine whether a gene will ultimately be lost or fixed. Fixation may relate to a specific nucleotide location in the DNA chain or a gene in general (locus).
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