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67 Cards in this Set
- Front
- Back
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what are genes?
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the basic units of inheritance, made of DNA. and located on the chromosomes.
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what is DNA comprised of?
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deoxyribose, a phosphate molecule and four types of nitrogenous bases, and the physical structure is a double helix.
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what do DNA bases code for?
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amino acids, which make up proteins, which are specified by triplet codons of nitrogenous bases.
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what is DNA replication based on?
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complimentary base pairing in which a single strand of DNA serves as the template for attracting bases that form a new strand of DNA.
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what is DNA polymerase?
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it is the primary enzyme involved in replication. it adds bases to the new DNA strand and performs "proofreading" functions.
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what is a mutation?
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an inherited alteration of genetic material ,like DNA.
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what are mutagens?
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substances that cause mutations
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what is the mutation rate in humans?
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it varies from locus to locus and ranges from 10-4 to 10-7 (negative) per gene, per generation.
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how are transcription and translation similar?
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they both are processes in which proteins are specified by DNA, both involve RNA.
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what is RNA?
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chemically similar to DNA, but is single stranded, has a ribose sugar molecule and has uracil rather than thymine as one as it's four nitrogenous bases.
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what is transcription?
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the process by which DNA specifies a sequence or messenger RNA (mRNA)
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what are introns and exons?
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since much of the RNA sequence from the mRNA before it leaves the nucleus, the excised sequences are called introns, and the ones that remain to code for proteins are called exons.
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what is translation?
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the procss by which RNA directs the process of synthesis of polypeptides, and this happens in the ribosomes (which is proteins and ribosomal RNA, (rRNA)
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what do human cells consist of?
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diploid somatic cells (body cells) and haploid gametes (sperm and egg cells)
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how many chromosomes do humans have?
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they have 23 pairs- 22 pairs are autosomes. The remaining pair is the sex chromosome, Females have two homologous XX, and makes have an X and Y chromosome.
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what is a karyotype?
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it is a ordered display of chromosomes arranged according to length and the location of the centromere.
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how often do major chromosomal abnormalities occur?
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about 1 in 150 live births, and it is the leading cause of mental retardation and miscarriage
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what is polyploidy?
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condition in which a euploid cell has some multiples of the nirmal number of chromosomes. Humans have been observed to have triploidy (3 copies of each chromosome) and tetraploidy( 4 copies of each chromosome) both conditions are lethal.
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what is aneuploid?
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somatic cells that do not have a multiple of 23, usually the result of nondisjunction
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what is trisomy?
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it is a type of aneuploidy in which one chromosome is present in three copies in somatic cells. A partial trisomy is one that only part of a chromosome is present in three copies
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what is monosomy?
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a type of aneuploidy in which one chromosome is present in only one copy in somatic cells. These cause more severe physical defects that trisomies.
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which is worse? loss of chromosomal material or duplication of chromosomal material?
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the LOSS of chromosomal material has more serious consequences that duplication. (Tis better to have too much than not enough)
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what is Down's syndrome?
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it is a trisomy of chromosome 21, and the best known chromosomal disease, and occurs in 1 out of 800 live births, and lore likely to occur in mothers over 35.
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which is worse? aneuploidies of the sex chromosomes, or the autosomes?
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Definitely the AUTOSOMES.
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what are some common sex chromosome aneuploidies?
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47 XXX, 45X (Turner syndrome), 47 XXY Klinefeltner syndrome, and 47 XYY karyotypes.
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what are some abnormalities of chromosomal structure?
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deletions, duplications, duplications, inversions, and translocations.
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what are Mendelian traits?
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caused by single genes, each of which occupies a position or locus, on a chromosome.
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what is an allelle?
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different forms of genes located at the same locus on a chromosome
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explain a locus on a somatic cell...
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at any given locus on a somatic cell, an person has 2 genes, one from each parent. a person may be homozygous of heterozygous for a locus
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what is a genotype?
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a person's genetic makeup
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what is a phenotype?
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reflects the interaction of genotype and environment
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what is the difference between a dominant and recessive gene?
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in a heterozygote, a dominant gene's effect masks those of a recessive gene. A recessive gene is expressed only when it is present in two copies.
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what pattern of genetic disease does a single gene cause?
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it follows autosomal dominant, autosomal recessive, or X-linked recessive modes of inheritance.
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what is a pedigree chart?
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it analyses modes of inheritance.
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what is recurrence risk?
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the probability of future offspring inheriting a genetic disease. For single gene disease, recurrence risks remain the same for each child regardless of the number of unaffected or affected children.
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what is the recurrence rate for autosomal dominant diseases?
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50%
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what is germline mosaicism?
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means that unaffected parents can produce multiple affected offspring. It happens because the germline of one parent is affected by mutation but the parents somatic cells are not affected
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can classical autosomal dormant diseases skip generations?
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NO.
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are makes and females equally likely to exhibit autosomal dominant disease and pass it on to their children?
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YES.
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can genetic diseases have a delayed onset?
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YES
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what is incomplete penetrance?
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a gene that is not always expressed phenotypically
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what is variable expressivity?
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it is a characteristic of many diseases.
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what is genomic imprinting?
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associated with methylation, results in differing expression of a disease gene, depending on which parent transmitted the gene.
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what is epigenetics?
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changes, such as methylation of DNA bases, that do not alter the DNA sequence, but can alter the expression of genes.
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true or false? Most parents of children with autosomal recessive genes are both heterozygous carriers of the recessive gene.
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TRUE
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what is the recurrence rate for autosomal recessive diseases?
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25%
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are males and females both equally likely to be affected by autosomal recessive disease?
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YES.
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what is consanguinity?
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sharing the common blood relative, and is common among families with autosomal recessive disease and more prevalent with rarer diseases. In first cousin matings, the frequency doubles.
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what happens in each normal female somatic cell early in embryogenesis?
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One of the two X chromosomes is inactivated. This is random, fixed and incomplete ( only part of the chromosome is actually inactivated), and may involve methyation
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how is gender determined embryonically?
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By the presence of the SRY gene on the Y chromosome. Embryos that have a Y chromosome 9 and thus lack the SRY gene) become males, and those lacking the Y chromosome, become females. when Y lacks SRY gene an XY female can be produced, and an X contains SRY gene an XX male is produced.
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what causes X-linked diseases?
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an X-linked recessive gene
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are males or females hemizygous for genes on the X chromosome?
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Males
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why are males much more likely to have X-linked diseases than females?
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because males need only one copy of the gene to express the desease.
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can fathers pass x-linked genes to their sons?
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NO.
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why can x-linked recessive diseases skip generations?
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because the genes can be transmitted through carrier females.
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what affects the recurrence risks for x-linked recessive diseases?
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the carrier and affected status of the mother and father
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what is a sex-limited trait?
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one that only affects only one gender
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what is a sex influenced trait?
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one that occur more often in one thsn the other
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what is crossover?
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during meosis I, crossover occurs and can cause recombinations of allelles located o the same chromosome
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how can you judge the distance between loci on the same gene?
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you can look for the frequency of recombinations to infer the distance.
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what is a marker locus?
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when it is closely linked to a disease-gene locus, it can be used to predict if a person will develop a genetic disease.
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what is included on a gene map?
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marker studies, gene cloning, studies of gene function, and interaction, and gene therapy
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what is a polygenic trait?
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it is the result of the combined effects of several loci, When environmental factors influence the train, it is multifactoral.
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what is the threshold of liability?
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many multifactoral traits have this,it means that once this has been crossed, the traits may be expressed.
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what are empiric risks?
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these are based on direct observation of many families to estimate the recurrence risk for multifactoral diseases.
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what raises the risk for multifactoral diseases?
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if more that one family member is affected, or, if the expressions of the disease in the proband is more severe
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Is recurrence risk high or lower for multifactoral diseases in more remote relatives?
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LOWER
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