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BIO170 - Obj 8 & 9
BIO170 - Obj 8, 9 - Genetics, monosomy, trisomy
| Question | Answer |
|---|---|
| What is DNA composed of? | pentose sugar (deoxyribose), phosphate molecule, and one of 4 nitrogenous bases |
| What are the 2 types of nitrogenous bases? Which bases are associated with each type? | the pyrimidines are thymine and cytosine; the purines are adenine and guanine |
| Which bases pair with which bases (i.e. complementary base pairing)? | adenine with thymine; cytosine with guanine |
| What is a mutation? | any inherited alteration of genetic material |
| What are the 3 types of mutations? | chromosome aberrations, base pair substitution, and frameshift mutation |
| What is a chromosome aberration? | any deviation from the normal # or morphology of chromosomes |
| What is base pair substitution? | one base pair is substituted for another; this is usually not apparent, it is subtle |
| What is a silent substitution? | a base pair substitution that does not result in an amino acid change |
| What is a frameshift mutation? What is the result? | The insertion or deletion of one or more base pairs; causes a change in the entire "reading frame" (genetic code is read 3 nucleotides at a time); causes either incorrect amino acid to be incorporated into polypeptide chains or premature chain termination |
| What is a spontaneous mutation? | mutation that occurs in absence of exposure to known mutagens |
| What is a mutagen? | any agent that promotes a mutation or causes an increase in the rate of mutational events (ex: radiation, chemicals) |
| What are mutational hotspots? | areas of the chromosomes that have high mutation rates; ex: CG (a cytosine base followed by a guanine base accounts for a higher percentage of disease-causing mutations) |
| How many chromosomes in somatic body cells? In somatic body cells during S-phase of cell cycle? In gametes? | somatic body cells contain 46 chromosomes (23 pairs); during S-phase, somatic body cells have 92 chromosomes (46 pairs); gametes have 23 chromosomes (not paired) |
| What are homologous chromosomes? | at conception, 1 chromosome is inherited from each parent; the homologous chromosomes look identical when examined with a microscope |
| What are diploid and haploid cells? | diploid cells are somatic cells - they contain 23 pairs of chromosomes; haploid cells are the gametes (sperm & ova); they contain 23 unpaired chromosomes |
| What is meiosis? | the formation of haploid cells from diploid cells |
| What are autosomes? | autosomal chromosomes; the 22 pairs of chromosomes, excluding the sex chromosomes are called autosomes and are homologous to each other |
| What are the sex chromosomes? | the non-autosomal chromosome is the sex chromosome (chromosome 23); in females it is a homologous pair (XX); in males it is a nonhomologous pair (XY) |
| Which parent determines the gender of the offspring? | the father (XY) |
| What is the name of a cell that has the correct number of chromosomes? | euploid cells are cells that have multiples of whole haploid (n) sets; ex, haploid cells (23n) and diploid (23*2n) are euploid forms |
| What is a polyploid cell? What are 2 examples? | a cell nucleus that contains 3 or more haploid cells (i.e. 3n or more); triploidy is a zygote having 69 chromosomes (23 *3n); tetraploidy is a zygote having 4 copies of each chromosome (23 *4n) = 92 |
| What is the usual result to triploid & tetraploid fetuses? | they normally don't survive |
| What are disjunction and nondisjunction? What are the effects of each? | disjunction-the normal separation of chromosomes during cell division -> euploid cells; nondisjunction-the failure of homologous chromosomes (sister chromatids) to separate normally during meiosis/mitosis -> aneuploid cells (the usual cause of aneuploidy) |
| What are the forms of chromosome aberrations? (3) | 1) polyploidy (multiples of EACH chromosome); 2) aneuploidy (doesn't have a multiple of 23 chromosomes - ex: monosomy (missing chromosome), trisomy (extra chromosome); 3) abnormalities of chromosome structure |
| What is an example of aneuploidy? What is the impact on the fetus? | trisomy - a cell containing 3 copies of one chrosome; infants can survive with trisomy of certain chromosomes; others will not; impairment is based on the chromosome in which the trisomy is found |
| What is Patau syndrome? | aka Trisomy D syndrome; Trisomy 13 syndrome; (47,13+) |
| What is the most common aneuploidy seen in spontaneous miscarriage? | Trisomy 16 (47, 16+) |
| What is Edwards syndrome? | Trisomy 18 (47, 18+) |
| What is the best-know example of aneuploidy? | Down syndrome which is a result of trisomy of chromosome 21 (47, 21+) |
| What is the largest risk factor for Down's syndrome? What are its effects? | risk increases with maternal age (total incidence is 1:800 live births); effects include mental retardation, low nasal bridge, epicanthal folds, protruding tongue, hypotonia (poor muscle tone) |
| What are universal signs & symptoms of all trisomies? | mental retardation and facial deformities |
| What is partial trisomy? | only an extra portion of a chromosome is present in each cell; consequences are not as severe as complete trisomy |
| What is a chromosome mosaic? | When trisomie occur in only some cells of the body; mitotic nondisjunction occurs in some embryonic cells, but not in others |
| What is Trisomy X? What are the effects? | 3 sex chromosomes: XXX; termed metafemales; effects: sterility, menstrual irregularity, intelligence lower than normal, tallness, twin Barr bodies in a single cell; more than 3 XXX -> more severe abnormalities (mental retardation & physical defects) |
| What is a Barr body? | in normal females, only one X chromosome seems to be activated; the other is a dark staining, inactive blob in the cell's nucleus, called a Barr body; buccal cells tend to show the presence of the Barr body |
| What is monosomy? What is the effect? | the presence of only one copy of any chromosome in a cell; monosomy is often lethal |
| What happens with monosomy of the sex chromosomes? | X is usually inherited from the mother; results in Turner syndrome (45, X) |
| What are the effects of Turner syndrome? | absence of ovaries (sterile), short stature (ex: 4'7"), webbing of the neck, edema, underdeveloped breasts, nipples set wide apart |
| What makes monosomy in the sex chromosome less serious? | if the Y chromosome is inactivated or not present; the Y chromosome carries little genetic material |
| In general, is it better to have extra chromosomal material or less? | it is better to have extra than less |
| What is Klinefelter syndrome? What is its usual cause? What are some variations? | individuals with at least 2 Xs and 1 Y chromosome; in most cases, it is caused by nondisjunction of the X chromosomes in the mother; variations: XXY, XXXY, XXXXY; abnormalities increase with each X; mosaicism can also be seen (XXY and XY) |
| What are the characteristics of Klinefelter syndrome? | phenotypically male, small testes (usually sterile), develop female-like breasts (gynecomastia), sparse body hair, long limbs, varying degree of mental retardation |
| What is trisomy in a phenotypical male? | 47 XYY; intelligence lower than normal, tallness, aggressiveness, acne; controversial evidence indicates that 1:30 male prisoners have XYY -> more violent? |
| What is the impact of chromosome breakage? (4 types) | althought physiological mechanisms will usually repair the break, the breaks often heal in a way that alters the structure of the chromosome; i.e. deletion, duplication, inversions, translocations |
| What is a clastogen? What are 3 examples? | an agent of chromosome breakage; ex: ionizing radiation, chemicals, viruses |
| What are the causes of chromosome deletion? What is an example of chromosome deletion? | broken chromosomes and loss of DNA cause deletions; ex: Cri du chat syndrome ("cry of the cat") |
| What causes Cri du chat syndrome? What are its manifestations? | deletion of short arm of chromosome 5 causes Cri du chat syndrome; major characteristic is high-pitched catlike whine; also, low birth weight, mental retardation, microcephaly, epicanthal folds, micrognathia, strabismus, hypertelorism |
| What are epicanthal folds, migrognathia, strabismus, and hypertelorism? | epicanthal folds: extra skin over outside corner of eyes; micrognathia: small lower jaw; strabismus: cross-eyed; hypertelorism: eyes are separated further apart |
| What is chromosome duplication? | presence of a repeated gene or gene sequence; rare occurrence; less sever that deletion (better to have more than less) |
| What happens in deletion of chromosome 5? In duplication? | deletion of the short arm of chromosome 5 causes Cri du chat; duplication causes mental retardation, but no physical abnormalities |
| What is a chromosome inversion? | no loss or gain of genetic material; there are 2 breaks on a chromosome; results in a reversal of the gene order as a segment of the chromosome is "flipped"; Ex: ABCDEFG may become ABEDCFG |
| What is the impact of a chromosome inversion? | the person may appear normal, but the chromosome may have an altered genetic expression; problems gets serious when an "inversion carrier" has an offspring |
| What is chromosomal translocation? What is the most important type of translocation? | the interchanging of genetic material between nonhomologous chromosomes; Robertsonian translocation is the most important type |
| Which chromosomes are most frequently translocated? Why? | translocation most typically occurs in chromosomes 13, 14, 15, 21, and 22 because these chromosomes have very small, short arms |
| How does translocation occur? | the centromere of 2 acrocentric (centromere is near the end) chromosomes appear to have fused, forming an abnormal chromosome consisting of the long arms of 2 nonhomologous chromosomes with the loss of short arms |
| How many chromosomes does a person with Robertsonian translocation have? What is the effect? | 45 chromosomes (2 have fused); they normally have a clinically normal phenotype (because of near normal chromosomal complement - short arms contain no essential genetic material), but risk of next generation having an unbalanced chromosomal complement |
| What happens to the offspring of a person with Robertsonian translocation? | they could have an unbalanced Robertsonian translocation and be trisomic for the long arm of the chromosome (i.e. inherits an extra copy of the long arm); (offspring can also be normal, or have a balanced translocation) |
| What trisomy is more frequent in Robertsonian translocation carriers? | 3-5 % of Down Syndrome (trisomy 21) cases are caused by Robertsonian translocation |
| What is a fragile site? | areas on chromosomes that develop distinctive breaks or gaps when cells are cultured (identifiable by a nonstaining gap); usually, fragile site is near the end of the long arm |
| What is Fragile X syndrome? | a fragile site on the long arm of the X chromosome; associated w/mental retardation; higher incidence in males because they have only 1 X chromosome |
| What are other manifestations of Fragile X syndrome? | face is long and narrow, large ears, prominent mandibular symphysis, high-arched palate, macroorchidism (edema in testicles), connective tissue abnormality, pes planus, dilation of the aorta, and mitral valve prolapse |
| What else is known about the chromosomal abnormality in Fragile X syndrome? | there is a high incidence of CGG repeats, duplicated again and again; successive generations have more repeats which is believed to lead to the expression of the Fragile X syndrome |
| How common is Fragile X syndrome? | it is second in occurrence to Down's syndrome |
| What is the difference between crossing over and translocation? | crossing over is a normal occurrence between homologous chromosomes; translocation is an interchanging of genetic info between non-homologous chromosomes |
| What is a locus? | the location/position of a gene on a chromosome |
| What is an allele? | a different form of a gene at a given locus; an allele of a gene is one of 2 or more forms of a given trait |
| What are some examples of alleles? | the gene for tongue rolling comes in 2 alleles (one allele allows tongue rolling, the other does not); also, HgbA vs Hgb S (Hgb A is normal hemoglobin; HgbS is for sickle cell anemia) |
| What is polymorphism? | a locus that has 2 or more alleles that occur w/appreciable frequency |
| What is homozygous? | when the loci on a pair of chromosome have identical genes; an individual who inherits 2 identical alleles of a given trait is designated as homozygous for that particular trait |
| What is heterozygous? | when the loci on a pair of chromosome have different genes |
| What does it mean for an allele to be dominant or recessive? How are dominant and recessive alleles represented? | if 2 alleles are found together, the allele that is observable is dominant and is represented by a capital letter; the one whose effects are hidden is recessive and is represented by a lowercase letter; the dominant trait will always be expressed |
| When is a recessive allele expressed? | only when an individual inherits 2 copies of it |
| What is a genotype? | the genetic makeup; what a person "has"; a person's genotype is the combination of genes inherited for a particular trait |
| What is a phenotype? | the observable, detectable appearance of the genes; ("what they demonstrate"); a person's phenotype is the expression of the genes inherited for a particular trait; that which can be seen or measured |
| Can you tell if a person is homozygous or heterzygous for a particular trait? | with a dominant gene, it is difficult; if an offspring of a tongue roller (dominant trait) can't roll his tongue, the tongue-rolling parent must be heterzygous for that trait (Tt) |
| What is codominance? | for some traits, there is no clear dominant allele; when these traits are passed on, each allele in a heterozygous pairing will be expressed, i.e. the 2 alleles are expressed equally |
| What is an example of codominance? | the ABO system for blood-typing; "A" and "B" are both dominant over "O", but A and B are co-dominant; if you have type A blood, you may be AA or AO; it you have AB blood, you have both A & B genes; if you have O blood, you are homozygous recessive OO |
| What is a carrier? What are examples of recessive diseases? | someone that has a disease gene but is phenotypically normal; sickle cell anemia (Ss is the carrier; ss demonstrates sickle cell disease) |
Created by:
debmurph
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