Genetics: C2 Flashcards
The human genome has approx. how much genes, which are the individual units of heredity of all traits?
25,000 genes
some sources est. 30,000-40,000 genes
What can contain one copy (N) of this genetic complement and are haploid?
Reproductive or germline cells
What can contain two complete copies (2N) and are diploid?
Somatic (non-germline) cells
What are organized into long segments of DNA, which, during cell division, are compacted into intricate structures with proteins to form chromosomes?
Gene
What has 46 chromosomes (22 pairs of autosomes, or non-sex chromosomes, and 1 pair of
sex chromosomes?
Each somatic cell
What can contain 22 autosomes and 1 sex chromosome, for a total of 23?
Germ cells (eggs, sperm)
At this, the full diploid chromosome complement of 46 is again realized in the embryo.
At fertilization
What is a functional unit that is regulated by transcription and encodes a RNA product, which is most commonly, but not always, translated into a protein that exerts activity within or outside the cell?
Gene
Genetic information in DNA is transmitted to daughter cells under two different circumstances:
1) Somatic cells divide by mitosis, allowing the diploid (2n) genome to replicate itself completely in
conjunction with cell division; and
2) Germ cells (sperm and ova) undergo meiosis, a process that enables the reduction of the diploid (2n) set of chromosomes to the haploid state (1n).
What has the function is to distribute and maintain the continuity of the genetic material in every cell of the body?
This results in equal distribution of the chromosomes to the two daughter cells.
Mitosis
Overview
● Prior to mitosis, cells exit the resting, or G0 state, and enter the cell cycle. After traversing a critical checkpoint in G1 cells undergo DNA synthesis (S phase), during
which the DNA in each chromosome is replicated, yielding two pairs of sister chromatids (2n –> 4).
● The process of DNA synthesis requires stringent fidelity in order to avoid transmitting errors to subsequent generations of cells.
● After completion of DNA synthesis, cells enter G2 and progress through a second checkpoint before entering mitosis.
● At this stage, the chromosomes condense and are aligned along the equatorial plate at metaphase.
● The two identical sister chromatids, held together at the centromere, divide and migrate to opposite poles of the cell.
● After formation of a nuclear membrane around the two separated sets of chromatids, the cell divides and two daughter cells are formed, thus restoring the diploid (2n) state.
Prior to mitosis, what happens to cells?
Cells exit the resting, or G0 state, and enter the cell cycle.
After traversing a critical checkpoint in G1, cells undergo:
DNA synthesis (S phase), during
which the DNA in each chromosome is replicated, yielding two pairs of sister chromatids (2n –> 4n)
The process of DNA synthesis requires
stringent fidelity in order to avoid transmitting errors to subsequent generations of cells.
After completion of DNA synthesis, cells enter what?
Enter G2 and progress through a second checkpoint before entering
mitosis.
At this stage, the chromosomes condense and are aligned along the equatorial plate at metaphase.
What are held together at the centromere, divide and migrate to opposite poles of the cell?
The two identical sister chromatids
After formation of a nuclear membrane around the two separated sets of chromatids, the cell divides and how many daughter cells are formed?
two daughter cells are formed, thus restoring the diploid (2n) state
duplicated chromosomes condense into microscopically visible bodies
Prophase
chromosomes continue to contract and line up on the metaphase plate (equatorial plate)
Metaphase
chromatids of the chromosomes separate at the centromeres and migrate to the opposite poles of the cell.
Anaphase
separated chromatids gather, a nuclear membrane forms around the separated sets and the cell divides, forming two daughter cells.
Telophase
Overview
Assortment and segregation of genes during meiosis.
● Meiosis occurs only in germ cells of the gonads.
○ It shares certain features with mitosis but involves two distinct steps of cell division that reduce the chromosome number to the haploid state.
○ In addition, there is active recombination that generates genetic diversity.
○ During the cell division, two sister chromatids (2n-›4n) are formed for each chromosome pair and there is an exchange of DNA between homologous paternal and maternal chromosomes.
○ This process involves the formation of chiasmata, structures that correspond to the DNA segments that cross over between the maternal and paternal homologues.
○ Usually there is at least one crossover on each chromosomal arm; recombination occurs more frequently in female meiosis than in male meiosis.
○ Subsequently, the chromosomes segregate randomly.
○ Because there are 23 chromosomes, there exist 2^23 (>8 million) possible combinations of chromosomes.
○ Together with the genetic exchanges that occur during recombination, chromosomal segregation generates tremendous diversity. and each gamete is genetically unique.
○ The process of recombination, and the independent segregation of chromosomes, provide the foundation for performing linkage analyses, whereby one attempts to correlate the inheritance of certain chromosomal regions (or linked genes) with the presence of a disease or genetic trait.
● After the first meiotic division, which results in two daughter cells (2n), the two chromatids of each chromosome separate during a second meiotic division to yield four gametes with a haploid state (1n).
○ When the egg is fertilized by sperm, the two haploid sets are combined, thereby restoring the diploid state (2n) in the zygote.
● In males, each primary spermatocyte forms four functional spermatids that develop into sperm, whereas in females, each oocyte forms only one ovum, the remaining products of meiosis being non - functional polar bodies.
● Processes fundamental to meiosis include chromosome
pairing, chromosome crossing over, and chromosome segregation.
○ These processes result in halving the chromosome number, regular distribution of chromosomes to daughter cells, and independent assortment of the genetic material from both the cross - over events and maternal - paternal homologue distribution in meiosis I, the ultimate result ensures genetic variability.
Meiosis occurs only in
germ cells of the gonads
○ It shares certain features with mitosis but involves two distinct steps of cell division that reduce the chromosome number to the haploid state.
○ In addition, there is active recombination that generates genetic diversity.
Meiosis