Term
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Definition
| A functional unit of inheritance; a region of DNA that codes for a product – either RNA or protein. |
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Term
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Definition
| Linear structure composed of DNA and protein and that carries genetic information. |
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Term
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Definition
| The position of a gene on a chromosome. |
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Term
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Definition
| An alternate form of a gene occupying the same locus; 2 alleles/diploid complement. |
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Term
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Definition
| A permanent, heritable change in the sequence of genomic DNA. Mutations can occur at either the molecular (BP mutation) or cytogenetic level (deletions, rearrangements, etc.). Mutations may give rise to new alleles. They are an important mechanism of population variation. |
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Term
| What is an example of a positive mutation? |
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Definition
| In countries with endemic malaria, individuals with sickle cell train tend to be healthier than normal individuals who are more susceptible to malaria. Unfortunately, being homozygous for the sickle cell mutation is a negative. |
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Term
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Definition
| A set of characteristics which occur together and are assumed to have a common basis. Not all characters occur in all affected individuals, and there is a range of variability within a population. For example, there are over 250 known features of velocadiofacial syndrome, but n single individual has all of those findings. However, for the diagnosis to be made, an individual diagnosed with a particular disorder must have a core group of the cardinal characters associated with that disease. |
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Term
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Definition
| Usually aimed at modification/alleviation of symptoms. |
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Term
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Definition
| The elimination of disease from an individual. At the present time, it is not possible to cure genetic disease. |
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Term
| Mitosis (somatic division) |
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Definition
| The process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 10% of the cell cycle. |
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Term
| What ploidy is a cell before undergoing DNA replication? |
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Definition
| Diploid (2N). The cell also has 2C DNA content (2 copies of DNA). |
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Term
| What ploidy is a cell immediately following DNA replication? |
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Definition
| 2N. However, because the DNA has replicated it has 2X the amount of DNA, so it is 4C. 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. |
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Term
| What ploidy is a cell following cell division? |
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Definition
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Term
| What are the stages of mitosis? |
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Definition
1) Interphase
2) Prophase
3) Metaphase
4) Anaphase
5) Telophase |
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Term
| During which stage of mitosis do the chromosomes shorten and thicken and may be visualized by light microscopy? |
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Definition
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Term
| During which stage of mitosis do the centromeres divide and the chromosomes separate? |
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Definition
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Term
| When does cytokinesis occur? |
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Definition
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Term
| What is the result of cytokinesis? |
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Definition
| 2 daughter cells that should be exact copies of the original parent cell. Each daughter cell should be 2N, 2C. |
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Term
| Assume a cell has 2 pairs of chromosomes, A and B. What will exist at metaphase? Following correct cytokinesis? |
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Definition
At metaphase, chromosomes A1, A2, B1, and B2 will exist.
Following cytokinesis, each daughter cell will receive one copy of each A1, A2, B1, and B2. |
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Term
| T or F: During mitosis, the cell alternates between periods of diploid and haploid ploidy. |
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Definition
| False! The cell is always diploid. |
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Term
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Definition
| A special type of cell division involving germ cells necessary for sexual reproduction. |
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Term
| Recombination (crossing over) |
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Definition
| Reassortment of genes between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can mesh with one another, and may exchange genetic information. The result is a reassortment of the genes/alleles present on each chromosome. |
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Term
| Where does meiosis occur? |
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Definition
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Term
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Definition
| A reduction by half of the original number of chromosomes during meiosis. 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. |
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Term
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Definition
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Term
| When does reduction division take place? |
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Definition
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Term
| When does crossing over happen in meiosis? |
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Definition
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Term
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Definition
| The failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes. |
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Term
| What happens if nondisjunction occurs during meiosis I? Use chromosomes A and B as an example. |
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Definition
| All gametes will be affected. If chromosomes A1 and A2 fail to separate at meiosis I, this will give rise to a cell with both A chromosomes (A1, A2, B2) and a cell with no chromosomes (B1 only). If the second division occurs correctly, the net result will be 4 cells with a chromosomal imbalance. Two cells will have an extra chromosome (A1, A2, B2) - these cells would be heterodisomic for chromosome A. The remaining two cells would be nullosomic for chromosome A. |
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Term
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Definition
| A cell that has two different copies of the same chromosome-- usually the result of nondisjunction during meiosis I. (e.g. Two gametes would have chromosomes A1 and A2, and two gametes would have no chromosome A. |
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Term
| What happens if nondisjunction occurs during meiosis II? Use chromosomes A and B as an example. |
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Definition
| Only one half of the gametes are affected by nondisjunction in meiosis II. When the gamete receives two (identical) replica copies of a single homolog of a chromosome, it is said to be isodisomic. One gamete has a single extra chromosome; one gamete is missing a single chromosome. |
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Term
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Definition
| Gametes missing a chromosome due to nondisjunction in meiosis I. |
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Term
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Definition
| When the child receives two (identical) replica copies of a single homolog of a chromosome. 2 chromosomes from the same source; duplication of 1 chromosome. This indicates nondisjunction during meiosis II. |
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Term
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Definition
| The process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitotic division of haploid gametogenous cells. |
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Term
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Definition
| The process by which male primary germ cells undergo division, and produce a number of cells termed spermatogonia, from which the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two spermatids or young spermatozoa. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa. |
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Term
| What are the types of cells present in each stage of spermatogenesis? |
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Definition
1) spermatogonium (2N/2C)
2) primary spermatocyte (2N/2C)
3) secondary spermatocyte (N/C)
4) spermatid (N/C) |
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Term
| What is the ploidy/number of chromosomes in spermatogonium? |
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Definition
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Term
| What is the process of multiplication for spermatogonia? |
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Definition
| Mitosis (spermatocytogenesis). |
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Term
| What is the ploidy/number of chromosomes in primary spermatocytes? |
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Definition
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Term
| What is the process of multiplication for primary spermatocytes? |
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Definition
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Term
| What is the ploidy/number of chromosomes in secondary spermatocytes? |
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Definition
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Term
| What is the process of multiplication for secondary spermatocytes? |
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Definition
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Term
| What is the ploidy/number of chromosomes in spermatids? |
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Definition
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Term
| What is the process of multiplication for spermatids? |
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Definition
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Term
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Definition
| The creation of an ovum (egg cell). It is the female form of gametogenesis. It involves the development of the various stages of the immature ovum. |
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Term
| What are the types of cells present in each stage of oogenesis? |
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Definition
1) Oogonia
2) Primary oocyte
3) Secondary oocyte
4) Ovum |
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Term
| What is the ploidy in oogonia? |
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Definition
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Term
| What is the process of multiplication for oogonia? |
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Definition
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Term
| What is the ploidy in primary oocytes? |
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Definition
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Term
| What is the process of multiplication for primary oocytes? |
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Definition
| Meiosis I (ootidogenesis). |
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Term
| What is the ploidy in secondary oocytes? |
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Definition
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Term
| What is the process of multiplication for secondary oocytes? |
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Definition
| Meiosis II (ootidogenesis). |
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Term
| What is the ploidy in ova? |
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Definition
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Term
| When does oogenesis begin? |
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Definition
| Oogenesis begins in the developing fetus and primary oocytes are present by the 3rd month of gestation. These cells reach dictyotene (prophase 1) by birth and remain so until ovulation. |
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Term
| When does the oocyte complete meiosis I? |
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Definition
| At ovulation, and thus becomes a secondary oocyte. |
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Term
| What is the difference between spermatocytes and oocytes in terms of production? |
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Definition
| Primary spermatocytes are produced throughout the male reproductive life, whereas primary oocytes are all present at birth. |
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Term
| What is the difference between the male and female gametes in terms of production? |
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Definition
| Male gametes (sperm) are produced continually, and female gametes (ova) are produced once per month. |
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Term
| How many gametes descend from both the male and female primary gametocyte? |
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Definition
Male: 4 equal gametes per primary gametocyte.
Female: 1 gamete per primary gametocyte. |
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Term
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Definition
| The science that combines the methods and findings of cytology and genetics. The study of heredity at the cellular level. |
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Term
| What is the prenatal clinical role of cytogenetics? |
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Definition
| To identify chromosomal anomalies that may be associated with disease and be able to distinguish normal variation from true abnormality |
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Term
| What are the effects of chromosomal abnormalities? |
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Definition
| Change in phenotype, fetal loss, genetic disease, malignancy, etc. |
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Term
| What are the statistics on fetal loss? |
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Definition
- 1 in 13 conceptions contain a chromosomal abnormality. Of these, 6 in 1000 are live born.
- 15% of recognized pregnancies end in spontaneous abortion- 80% in the first trimester.
- Of the spontaneous losses, 60% are chromosomal.
- Of the chromosomal losses, 52% are autosomal trisomies. |
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Term
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Definition
| A medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid, which contains fetal tissues, is extracted from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for genetic abnormalities. |
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Term
| What is the postnatal clinical role of cytogenetics? |
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Definition
About 0.6% of newborns have a chromosome anomaly.
- features of a known chromosomal disorder
- ambiguous genitalia
- multiple congenital anomalies |
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Term
| What is the role of cytogenetics in children and adults? |
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Definition
| Characterization of the family history of a chromosomal disorder and identify features of a known chromosomal disorder (e.g. mental retardation, infertility, some malignancies, etc.). |
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Term
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Definition
| Chromosome pairs of the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the organism's mother; the other from the organism's father. |
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Term
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Definition
| A form of aneuploidy with the presence of only one chromosome (instead of the typical two in humans) from a pair.[1] Partial monosomy occurs when only a portion of the chromosome has one copy, while the rest has two copies. |
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Term
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Definition
| A genetic abnormality (aneuploidy) in which there are three copies, instead of the normal two, of a particular chromosome. |
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Term
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Definition
| Results in 69 chromosomes (sometimes called 69,XXX) (or tetraploidy with 92 chromosomes (sometimes called 92,XXXX)). Triploidy, usually due to polyspermy (an egg that has been fertilized by more than one sperm), occurs in about 2–3% of all human pregnancies and ~15% of miscarriages. The vast majority of triploid conceptions end as miscarriage and those that do survive to term typically die shortly after birth. In some cases survival past birth may occur longer if there is mixoploidy with both a diploid and a triploid cell population present. |
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Term
| Chromosomal translocation |
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Definition
| A chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer. |
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Term
| Deletion (chromosomal abnormality) |
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Definition
| A mutation (a genetic aberration) in which a part of a chromosome or a sequence of DNA is missing. Deletion is the loss of genetic material. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. Deletions can be caused by errors in chromosomal crossover during meiosis. This causes several serious genetic diseases. Deletion is also causing frameshift. |
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Term
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Definition
| A chromosome whose arms have fused together to form a ring. A ring chromosome is denoted by the symbol r. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, they may also arise spontaneously during development. |
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Term
| How do we identify chromosomal abnormalities? |
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Definition
1) Size
2) Centromere position
3) Banding pattern (karyotype) |
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Term
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Definition
| A metaphase chromosome whose two arms are roughly equal in length is said to be metacentric. |
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Term
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Definition
| A metaphase chromosome whose two arms are unequal in length is said to be submetacentric. |
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Term
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Definition
| If the p (short) chromosomal arm is so short that it is hard to observe, but still present, then the chromosome is acrocentric. The human genome includes five acrocentric chromosomes: 13, 14, 15, 21 and 22. |
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Term
| What is the point of reference to determine relative lengths of chromosomal arms. |
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Definition
| The position of the centromere. |
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Term
| P (in metaphase chromosome morphology) |
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Definition
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Term
| Q (in metaphase chromosome morphology) |
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Definition
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Term
| Where are the rRNA genes found? |
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Definition
| On the modified short arm of acrocentric chromosomes (below the satellite (modified telomere)) 13, 14, 15, 21 and 22. |
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Term
| Nucleolus organizer region |
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Definition
| A chromosomal region around which the nucleolus forms. This region is the particular part of a chromosome that is associated with a nucleolus after the nucleus divides. The region contains several tandem copies of ribosomal RNA genes. In humans, the NOR contains genes for 5.8S, 18S, and 28S rRNA clustered on the short arms of chromosomes 13, 14, 15, 21 and 22 (the acrocentric chromosomes). |
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Term
| Stalk (acrocentric chromosomes) |
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Definition
| The location of the nucleolus organizer region (NOR). |
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Term
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Definition
| A chromosome whose centromere is located at the terminal end of the chromosome. Telocentric chromosomes do not exist in humans. |
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Term
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Definition
| A region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. The telomere regions deter the degradation of genes near the ends of chromosomes by allowing for the shortening of chromosome ends, which necessarily occurs during chromosome replication. Over time, due to each cell division, the telomere ends do become shorter. |
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Term
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Definition
| The presence of two or more alternative structural forms for a chromosome that occurs in a frequency of at least 1% within a population. These are inherited as Mendelian characters and can be traced through pedigrees. The variation is usually not associated with specific clinical anomalies or a particular disease. |
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Term
| How many chromosomes exist in a somatic cell? |
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Definition
| 46 (23 pairs x 2): Of these, 22 pairs are autosomes, 1 pair is a sex chromosome including X and Y chromosomes. |
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Term
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Definition
| Having sex chromosomes that do not differ in morphology: XX for females. |
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Term
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Definition
| Having sex chromosomes that differ in morphology: XY for males. |
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Term
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Definition
| Homologous sequences of nucleotides on the X and Y chromosomes that exist on the distal ends of their short arms. These genes are inherited and recombination may take place, occasionally leading to a genetic imbalance. |
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Term
| Sex determining region of the Y (SRY) |
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Definition
| Sex determining region of the Y chromosome located just below the pseudoautosomal region. SRY encodes for testis-determining factor (TDF) protein. |
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Term
| Testis determining factor (TDF) |
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Definition
| A protein encoded by the SRY gene which results in maleness in humans. |
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Term
What nomenclature would you use to describe a chromosome complement?
How would you describe a normal female? A normal male? |
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Definition
1) The total number of chromosomes
2) The sex chromosome complement
3) Any chromosome abnormalities.
These units are listed in order and separated by commas. For example:
46,XX is a normal female
46,XY is a normal male |
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Term
| How would you describe trisomy 13 in a female using the correct nomenclature? |
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Definition
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Term
| How would you describe monosomy 8 in a male using the correct nomenclature? |
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Definition
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Term
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Definition
| One of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division (mitosis or meiosis). They are called sister chromatids so long as they are joined by the centromeres. When they separate (during anaphase of mitosis and anaphase 2 of meiosis), the strands are called daughter chromosomes. Chromatids contain all the genetic material equivalent to a chromosome. They are usually seen at metaphase. In other words, a chromatid is "one-half of a replicated chromosome". |
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Term
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Definition
| A region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment. The sister chromatids are attached all along their length, but they are closest at the centromere. |
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Term
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Definition
| An image of the chromosome constitution of an individual. Also, a figure showing the paired chromosomes from a cell arrayed in a standard sequence. |
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Term
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Definition
| The presence of 2 chromosomes. |
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Term
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Definition
| A mutation present in every cell of the body. An individual with a constitutional mutation may pass that mutation on to their progeny by germ-line transmission. |
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Term
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Definition
| Somatic cell division in which the DNA replicates and is evenly distributed to two equal daughter cells. |
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