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Definition
| a chromosome whose centromere is close to the end of one arm |
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Definition
| condition in which the number of chromosomes is not a multiple of 23 (for humans), as in trisomy and monosomy |
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Definition
| the 22 pairs of chromosomes excluding the sex chromosomes |
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Definition
| region of a chromosome that separates the two arms. they are the sites of attachment of spindle fibers during cell division |
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Definition
| two parallel identical strands, connected at the centromere, of the doubled chromosome after DNA replication but before anaphase |
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Definition
| loss of chromosome material. may be terminal or interstitial |
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Definition
| structural rearrangement of a chromosome in which two breaks occur, followed by the reinsertion of the chromosome segment, but in reversed order. |
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Definition
| does not include the centromere |
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Definition
| does include the centromere |
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Definition
| cell division process in which haploid gametes are formed from diploid germ cells |
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Definition
| aneuploid condition in which a specific chromosome is present in only a single copy |
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Definition
| occurrence among offspring of new combinations of alleles, resulting from crossovers that occur during parental meiosis |
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Term
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Definition
| occurrence among offspring of new combinations of alleles, resulting from crossovers that occur during parental meiosis |
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Term
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Definition
| distribution of genes from homologous chromosomes to different gametes during meiosis |
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Definition
| relocation of genetic material from one chromosome to another |
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Term
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Definition
| translocation resulting from breaks on two different chromosomes and a subsequent exchange of material. Carriers of balanced reciprocal translocations maintain the normal number of chromosomes and normal amount of chromosome material. |
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Term
| Robertsonian translocation |
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Definition
| translocation in which the long arms of two acrocentric chromosomes become fused at the centromere to form a single chromosome. The short arms of the original chromosomes are lost. The translocation carrier thus has only 45 chromosomes instead of 46 but is phenotypically normal because the short-arms contain no essential genetic material |
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Term
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Definition
| aneuploid condition in which the individual has an extra copy of one chromosome |
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Definition
| site of crossing over in meiosis |
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Definition
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Term
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Definition
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Term
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Definition
| light bands are euchromatin. dark bands are heterochromatin |
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Term
| Common causes of polyploidy |
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Definition
| Fertilization of the same ovum by two or more sperm or from errors in maternal meiosis II that result in an egg with a diploid number of chromosomes, which is then fertilized by a sperm with a haploid number of chromosomes |
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Term
| How to tell if nondisjunction occurred in Meiosis I or II |
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Definition
| When nondisjunction occurs in Meiosis 1, the chromatids in the gametes will be different. If it occurs in Meiosis 2, the chromatids in the gametes will be the same. Probes for the three different chromatids can show at which stage the nondisjunction occurred. |
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Term
| Trisomies where live birth can occur |
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Definition
| trisomy of 13, 18 and 21 (Down's Syndrome) |
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Term
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Definition
| Occur when there is abnormal centromere division, which may result in either duplication of the short arm and deletion of the long arm (iso-p), or a duplication of the long arm and deletion of the short arm (iso-q). There is a loss of genetic material with these chromosomes |
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Term
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Definition
| Gold Standard, 0.5% risk of procedure-induced pregnancy loss, Perform at 15-16 weeks gestation, Amniotic fluid is obtained using ultrasound to guide the placement of the needle in the uterus |
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Term
| Chorionic Villus Sampling |
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Definition
Performed at 10-12 weeks gestation,
Has a 0.5% risk of procedure induced pregnancy loss, Removed cells are from the placenta (chorion), although they are contaminated with maternal cells. Ultrasound is used to guide needle placement. A separation procedure is required to remove maternal cells from the sample |
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Term
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Definition
Umbilical blood sampling; used if inconclusive results are obtained by other procedures. Ultrasound guides needle into the umbilical artery (obtain blood instead of amniotic fluid).
Performed after 18 weeks of gestation
Has a high rate of fetal loss: 1-2%
Advantage is less time is required to obtain results |
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