2: Intro to Cytogenetics Flashcards
____ is the study of heredity at the cellular level.
Cytogenetics is the study of heredity at the cellular level.
Somatic division, or mitosis, results in duplication of the contents of the cell, including the DNA, followed by cytokinesis, or separation of the materials into two new daughter cells. With respect to the DNA content, the original cell is diploid (2N). After the DNA replicates, the DNA content becomes 4N, but the original constitution ___N is reestablished following division.
Somatic division, or mitosis, results in duplication of the contents of the cell, including the DNA, followed by cytokinesis, or separation of the materials into two new daughter cells. With respect to the DNA content, the original cell is diploid (2N). After the DNA replicates, the DNA content becomes 4N, but the original constitution (2N) is reestablished following division.
There are five basic steps in mitosis: Interphase, Prophase, Metaphase, Anaphase, and Telophase. You have heard about the regulatory control of mitosis from Dr. Mitchell.
For cytogenetics, the most important phase of cell division is ______.
At interphase, the DNA replicates so the 2N cell becomes ___C. The newly replicated chromatids are held together and appear as one structure, so there is __ increase in the number of chromosomes although the DNA content has ____.
The chromosomes shorten and thicken and can be visualized by light microscopy at ____.
The centromeres divide and the chromosomes separate in _____.
Cytokinesis, the final step in cell division, occurs in _____. The net result is 2 daughter cells that should be copies of the original parent cell. Each daughter cell is __N.
There are five basic steps in mitosis: Interphase, Prophase, Metaphase, Anaphase, and Telophase. You have heard about the regulatory control of mitosis from Dr. Mitchell.
For cytogenetics, the most important phase of cell division is metaphase.
At interphase, the DNA replicates so the 2N cell becomes 4C (chromatids). The newly replicated chromatids are held together and appear as one structure, so there is no increase in the number of chromosomes although the DNA content has doubled.
The chromosomes shorten and thicken and can be visualized by light microscopy at metaphase.
The centromeres divide and the chromosomes separate in anaphase.
Cytokinesis, the final step in cell division, occurs in telophase. The net result is 2 daughter cells that should be copies of the original parent cell. Each daughter cell is 2N.
LidMeosis I & II
Germ cells undergo a different type of cell division known as meiosis. This occurs in the gonads. There are two very important events that occur in meiosis. _____ of linked alleles leads to the reassortment of the genes.
The hallmark of meiosis is _______ which is a reduction by half of the original number of chromosomes. This is accomplished by two consecutive cell divisions, but only a single DNA duplication. Thus, the cell begins as 2N, but the final products are N.
Meosis I: -prophase I-recombination -metaphase I -anaphaseI- reduction division -telophase I Meosis II: -metaphase II -anaphase II -telophase II
Germ cells undergo a different type of cell division known as meiosis. This occurs in the gonads. There are two very important events that occur in meiosis. Recombination of linked alleles leads to the reassortment of the genes.
The hallmark of meiosis is reduction division which is a reduction by half of the original number of chromosomes. This is accomplished by two consecutive cell divisions, but only a single DNA duplication. Thus, the cell begins as 2N, but the final products are N.
Recombination results when portions of two homologs break and exchange places. This has been visualized and the event is known as crossing-over. Crossover – an exchange between _____ chromosomes resulting in a reassortment of the genes/alleles present on each chromosome.
Recombination results when portions of two homologs break and exchange places. This has been visualized and the event is known as crossing-over. Crossover – an exchange between homologous chromosomes resulting in a reassortment of the genes/alleles present on each chromosome.
See Pg. 31 - 33
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In females, X inactivation should be _____. That is, approximately half of the cells express one allele, and the other half express the second allele. There will be some statistical variance from this, and within a population of individuals, you would most likely see a bell curve distribution.
However, deletion or damage to one of the X chromosomes can lead to a change in the inactivation patterns. A damaged X may be preferentially ______, skewing the distribution such that the alleles on the other X chromosome are always expressed. This is non-random X inactivation, which can result in clinical problems.
In females, X inactivation should be random. That is, approximately half of the cells express one allele, and the other half express the second allele. There will be some statistical variance from this, and within a population of individuals, you would most likely see a bell curve distribution.
However, deletion or damage to one of the X chromosomes can lead to a change in the inactivation patterns. A damaged X may be preferentially inactivated, skewing the distribution such that the alleles on the other X chromosome are always expressed. This is non-random X inactivation, which can result in clinical problems.
_____, failure of the chromosome or chromatids to disjoin properly, can occur.
Nondisjunction, failure of the chromosome or chromatids to disjoin properly, can occur.
Disomy is the presence of _ chromosomes
Isodisomy: 2 chromosomes from the ____ source ==> _____ of 1 chromosome
Heterodisomy: 2 ____ chromosomes
Disomy is the presence of 2 chromosomes
Isodisomy: 2 chromosomes from the same source ==> duplication of 1 chromosome
Heterodisomy: 2 different chromosomes
Nondisjunction of the “A” chromosomes in Meiosis I results in ___ disomic (A1 + A2) and ___ nullosomic (no A chromosome) gametes
Nondisjunction of the “A” chromosomes in Meiosis I results in two disomic (A1 + A2) and two nullosomic (no A chromosome) gametes
Nondisjunction in meiosis 2 has a four cell distribution of A1 B2, A1 B2, B1, B1 A2 A2 = ,,,.
Nondisjunction in meiosis 2 has a four cell distribution of A1 B2, A1 B2, B1, B1 A2 A2 = 2, 2, 1, 3.
Spermatogenesis occurs in males and produces sperm. Oogenesis occurs in females and produces the eggs.
These processes are a combination of mitosis and meiosis.
In spermatogenesis, an original germ cell replicates via mitosis to generate a large population of spermatogonia which are 2N. At some point, one of these cells will enter meiotic division. The DNA replicates giving a ______ spermatocyte. This cell divides and following reduction division becomes a ____ spermatocyte. The second meiotic division results in ____ spermatids which will mature into sperm. Each primary spermatocyte gives rise to __ spermatids. This is a classic meiotic division.
Spermatogenesis occurs in males and produces sperm. Oogenesis occurs in females and produces the eggs.
These processes are a combination of mitosis and meiosis.
In spermatogenesis, an original germ cell replicates via mitosis to generate a large population of spermatogonia which are 2N. At some point, one of these cells will enter meiotic division. The DNA replicates giving a primary spermatocyte. This cell divides and following reduction division becomes a secondary spermatocyte. The second meiotic division results in haploid spermatids which will mature into sperm. Each primary spermatocyte gives rise to 4 spermatids. This is a classic meiotic division.
Primary Oocytes reach prophase _ by birth and remain there until ovulation.
Oogonia (2N) replicate via ______. One of these cells will enter meiosis and become a ______ oocyte.
The first meiotic division results in two ______ daughter cells.
Both daughters receive equal halves of the DNA, but one daughter receives the ______ of the cytoplasm. This is the _____ oocyte. The daughter with little cytoplasm is known as the _____ polar body. This cell usually degrades, though it can go through a second division giving rise to _____ polar bodies.
The remaining functional cell, the secondary oocyte, goes through the second _____ division, again giving equal parts of the DNA to two daughter cells, but an unequal allocation of cytoplasm. The cell receiving most of the cytoplasm is the ____ cell, and the other is a second polar body. None of the polar bodies function as ____. Thus, in oogenesis, the original oocyte gives rise to only one functional gamete. Meiosis is not completed until ____.
Primary Oocytes reach prophase 1 by birth and remain there until ovulation.
Oogonia (2N) replicate via mitosis. One of these cells will enter meiosis and become a primary oocyte.
The first meiotic division results in two unequal daughter cells.
Both daughters receive equal halves of the DNA, but one daughter receives the majority of the cytoplasm. This is the secondary oocyte. The daughter with little cytoplasm is known as the first polar body. This cell usually degrades, though it can go through a second division giving rise to secondary polar bodies.
The remaining functional cell, the secondary oocyte, goes through the second meiotic division, again giving equal parts of the DNA to two daughter cells, but an unequal allocation of cytoplasm. The cell receiving most of the cytoplasm is the egg cell, and the other is a second polar body. None of the polar bodies function as gametes. Thus, in oogenesis, the original oocyte gives rise to only one functional gamete. Meiosis is not completed until fertilization.
Timing of oogenesis is also quite interesting. Oogenesis begins in the developing fetus. By the 3rd month of gestation, the primary oocytes are present. These cells reach dictyotene (prophase 1) by birth and remain so until ovulation – up to 50 years later! At ovulation, the oocyte completes meiosis _, becoming a ____ oocyte. Meiosis will only be completed if _____ occurs. Penetration of the sperm head stimulates the final division and ______ of the second polar body. It is then possible for the male and female pronuclei to fusion creating a zygote.
Important points:
In females, meiosis is not completed until ______.
Fertilization triggers final division of the _____; _____ polar body is separated
Sperm head breaks down, releasing the male _____
Fusion of the male and female ______ will result in zygote formation
Timing of oogenesis is also quite interesting. Oogenesis begins in the developing fetus. By the 3rd month of gestation, the primary oocytes are present. These cells reach dictyotene (prophase 1) by birth and remain so until ovulation – up to 50 years later! At ovulation, the oocyte completes meiosis I, becoming a secondary oocyte. Meiosis will only be completed if fertilization occurs. Penetration of the sperm head stimulates the final division and release of the second polar body. It is then possible for the male and female pronuclei to fusion creating a zygote.
Important points:
In females, meiosis is not completed until fertilization.
Fertilization triggers final division of the egg; secondary polar body is separated
Sperm head breaks down, releasing the male pronucleus
Fusion of the male and female pronuclei will result in zygote formation
Of the 46 chromosomes (23 pairs) in a somatic cell, there are __ pairs of autosomes. There is 1 pair of sex chromosomes including X and Y chromosomes.
Females are ____gametic: XX
Males are ______gametic: XY
Of the 46 chromosomes (23 pairs) in a somatic cell, there are __ pairs of autosomes. There is 1 pair of sex chromosomes including X and Y chromosomes.
Females are homogametic: XX
Males are heterogametic: XY
