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55 Cards in this Set
- Front
- Back
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What is a congenital abnormality? |
A birth defect. A condition affecting a child that occurs in the womb. |
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Classifications of congenital abnormalities |
-malformation -disruption -deformation -syndrome -sequence -dysplasia -association |
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What is meant by malformation? |
A primary structural defect. Usually a single organ showing multifactorial inheritance (many factors, both genetic and environmental) |
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What is meant by disruption? |
A secondary structural defect of an organ or tissue. Usually caused by environmental factors such as trauma, infection or ischaemia. |
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What is meant by deformation? |
An abnormal mechanical force that distorts a structure. Usually occurs during late pregnancy and has a good prognosis as the organ has a normal structure but oddly shaped. |
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What is meant by syndrome? |
A consistent pattern of abnormalities with a specific underlying cause. E.g. chromosomal abnormalities. |
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What is meant by sequence? |
Multiple abnormalities initiated by a primary factor. Initial factor can be environmental or genetic. |
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What is meant by dysplasia? |
An abnormal organistion of cells in tissues. |
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What is meant by association? |
A non-random ocurence of abnormalities not explained by a syndrome (the cause isn't known) |
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Number of chromosomes in a haploid cell |
23. 22 autosomes 1 sex chromosome |
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Number of chromosomes in a diploid cell |
46. One haploid set from each parent. |
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What is a centromere? |
The point of attachment between sister chromatids in mitotic chromosomes |
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What isa chromosome with the centromere in the middle called? |
Metacentric |
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What is a chromosome with the centromere just off the middle called? |
Submetacentric |
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What is a chromosome with the centromere not in the middle called? |
Acrocentric |
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In an acrocentric chromosome, what are the small ends of thr chromatids called? |
Sattelites |
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Number of chromosomes in the karyotype of a somatic cell? |
46 |
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Number of chromosomes in the karyotype of a sex cell? |
23 |
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Name of the short arm of a chromosome |
p |
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Name of the long arm of a chromosome |
q |
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What is used to image karyotypes? |
FISH Fluorescent in-situ hybridisation |
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What are the 3 types of chromosomal abnormailites? |
-numerical/aneuploidy -structural -mosaicism |
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What is meant by aneuploidy? |
The loss or gain of a chromosome/ chromosomes |
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What are the types of structural chromosomal abnormalities? |
-translocations -deletions -insertions -inversions -rings |
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What is meant by mosaicism? |
Having different cell lines. Shows the presence of multiple populations with different genotypes in a single individual. |
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Types of autosomal aneuploidy |
-monosomy -trisomy -tetrasomy |
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What is monosomy? |
The loss of a single chromosome. Almost always lethal. |
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What is trisomy? |
The gain of one chromosome. Tolerable. |
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What is tetrasomy? |
The gain of 2 chromosomes. Tolerable. |
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Why is chromosome gain better tolerated that chromosome loss? |
Dosage compensation. Loss results in a 50% reduction in fully expressed gene products while a gain results in only a 33% increase. |
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What is meant by partial aneuploidy-transloaction? |
When part of a chromosome is translocated to another chromosome |
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What is meant by a balanced translocation? |
When there is an even exchange of genetic material between the two chromosomes so no genetic material is lost |
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What is meant by an unbalanced translocation? |
When there is not an even exchange of genetic material between chromosomes, leading to the loss or gain of gentic information |
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What is meant by a chromosome derivative? |
A chromosome of that number but which has been modified |
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What is meant by recipricol translocation? |
Gentic material is swapped between chromosomes |
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What causes down syndrome? |
Trisomy 21 (An extra chromosome 21) |
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What correlates with risk of down syndrome? |
Advancing maternal age |
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Newborn features if down syndrome |
Severe hypotonia, sleepy, excess nuchal skin |
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Craniofacial features of down syndrome |
Macroglossia (big tongue), small ears, epicanthic folds, upward sloping palpebral fissures (gap between upper and lower eyelids) and brishfield spots (white spots in iris) |
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Limb features of down syndrome |
Single palmar crease, wide gap between the first and second toes |
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Cardiac features of down syndrome |
Atrial and ventricular defects |
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Other features of down syndrome |
Short stature, duodenal atresia. Increased risk of leukaemia and Alzheimer's. Often happy and affectionate, with advanced social skills |
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Causes of down syndrome |
95% of cases caused by trisomy 21 with a 90% maternal origin of the extra chromosome. This is due to the non-disjunction of homologous chromosomes in meiosis I Also due to a Robertsonian translocation, with the breakage of acrocentric chromosomes and the fusion of their long arms. Rarely due to mosaicism caused by mitotic disjunction in the zygote, in which case they are less severely affected as not all cells have the genotype causing the condition. |
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Another name for monosomy X |
Turner's syndrome |
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How can Turner's syndrome be detected in unborn females? |
can be detected from the 2nd trimester with generalised oedema and swelling in the neck. |
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Features of Turner's syndrome |
Short stature Ovarian failure Low posterior hairline Short 4th metacarpals Webbed neck Aorta defect |
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Causes of Turner's syndrome |
Usually caused by the loss of the x or y chromosome in paternal meiosis. Can also be due to a ring chromosome, single arm deletion or mosaicism. |
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What is meant by a ring chromosome |
When there when there are breaks that are on the end of two arms of chromosome and the sticky ends are then joined and fragments are lost. Often unstable at mitosis and so mosaicism is frequent. Some cells have the ring and others are monosomic |
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Why can people survive with only one x chromosome |
Dosage compensation is different in sex chromosomes. In normal females one of the X chromosomes is inactivated anyway |
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Features of polysomy in females |
X x x will often have no physical abnormalities, normal fertility and only a small IQ points decrease. Those with 4 or more x chromosomes will show mental retardation |
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Features of polysomy in males |
Klinefelter's syndrome (xxy) results in clumsiness, verbal learning disability, being taller than average, infertility, increased risk of leg ulcers, osteoporosis and breast carcinoma in later life. Some will also develop gynaecomastia (breasts). The extra x can come from a male or female. Having more than 2XS is possible but rare |
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How can people be chromosomally one gender but phenotypically the opposite? |
The SRY gene causes development of the testes. translocation of this gene to the x chromosome in SRY recombination can cause XX males with SRY (sterile since genes required for spermatogenesis are on the y chromosome) or XY females without SRY (also infertile) |
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What does SRY stand for |
Sex determining region on the Y |
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What is di George syndrome |
The most common microdeletion disorder(of 22q11) which causes velocardiofacial (VCFS) /Sedlackova syndrome and can cause congenital heart disease, palatal abnormalities, (para/)thymic hypoplasia, characteristic faces and learning disabilities |
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What is cri du chat syndrome |
A rare deletion mutation which causes microcephaly, hypertelorism, micrognathia, epicanthal Folds, low set ears, hypotonia, severe psychomotor and mental retardation and a characteristic cat-like cry in newborn's |
