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33 Cards in this Set
- Front
- Back
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What is cross over?
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Recombination; homologous pairs exchange genes during meiosisI (4 strand stage)->4 products (2 recombinant, 2 nonrecombinant)
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What is cross over?
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Recombination; homologous pairs exchange genes during meiosisI (4 strand stage)->4 products (2 recombinant, 2 nonrecombinant)
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What is genetic linkage?
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The tendency for alleles that are close together to be transmitted together
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What is lyonization?
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"Random" X inactivation; condenses to form Barr body attached to nuclear membrane. Late replicating
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How do you determine the # of Barr bodies?
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The # of X chrom minus 1
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What are the features of X inactivation?
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Abnormal X chrom are preferentially inactivated. With balanced X-autisome translocations the normal X is usually inactivated, inactivating the x-autosome translocated chrom is lethal, x unactivation is permanent in most somatic cells but reversible in germ cells
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Is X-chrom expression mosaic?
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Functionally all females are mosaic for X-chrom expression
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What is skewed lyonization?
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When the inactivation process maybe skewed a woman may have a larger than avg proportion of her cells with the mutated gene on the active x-chrom->"manifesting female carrier" shows signs of the disorder
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Why does Turner syndrome occur since only 1 X-chrom is normally active?
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2 active x-chrom are needed for normal ovarian fcn
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What is the psuedoautosomal region of sex chrom?
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9 Genes located here are inherited just like any autosomal gene. Males have 2 copies of these genes (1 on Y & 1 on X) so they can inherit an allele originally present on the X chrom of their father. Females can ingerit an allele orig on Y of their father. Guarantees disjcn of X-Y chrom during gametogenesis
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What is mosaicism?
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Not every cell has the same genotype
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What is somatic mosaicism?
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Mutation occurs after conception. Varies in the # of cells involved
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What is germ cell mosaicism?
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Post-conceptional mutation. Mutation limited to germ cells. Parent is asymptomatic but condition is inheritable
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What explains proposed recessive conditions that have unaffected parents but multiple affected children?
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Dominant conditions w/ Germ cell mosaicism
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What is the possible explanation for autosomal recessive syndromes w/ atypical growth or development?
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Uniparental disomy (2/1000 CF cases are maternal UPD). 2 copies of a chrom comefrom the same parent
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What is isodisomy?
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Same chromosome
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What is heterodisomy?
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Diff chrom
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What are the possible causes of uniparental disomy?
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Post-fertilization event , monosomic conception w/ subseq gain, trisomic conception w/ subseq loss, or gamete complementation
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What is gamete complementaion?
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The gamete form 1 parent contains both chrom. The centromeres will be heterodisomic if from meiosis I error or isodisomic if from meiosis II error
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What is genetic imprinting?
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Differential expression of the paternal vs materanl DNA; monoallelic expression
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What are some clues to imprinting?
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Differential expression of chrom deletions & triploidy
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What are 2 examples of genetic imprinting?
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Prader-Will & Angelman's syndromes
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What are the clinical features of Prader Willi?
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congential hypotonia, hypogonadism, mental retardation (mild to moderate), & obesity
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What are the clinical features of Angelman's?
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Severemental retardation, periods of unprovoked laughter, absent speech, microcephaly, ataxic gait
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Describe the molec cytogenetics of Prader-Willi?
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15q11-13 deletion, deletion always paternal, some have maternal isodisomy
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Describe molec cytogenetics of Angelman's.
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15q11-13 deletion, deletion always maternal, uniparental disomy rare (paternal when present)
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What are the clinical features of triploidy?
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Miscarriage, large cystic placenta & late loss if 2 paternal & 1 maternal (fetus w/ IUGR, macrocephaly, syndactyly), small placenta & early loss if 2 maternal 1 paternal
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Summarize the clinical features of triploidy.
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Paternal genes important in placentation & maternal genes important on embryogenesis
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What is the role of DNA methylation in imprinting?
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The most common mech of imprinting involves differential methylation of allels. Methylation of a locus may have + or - effect
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What can be a mech of transcriptional silencing?
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DNA methylation of CpG dinucleotides in the promoter region
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What are some possible reasons for imprinting?
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Normal reg of placentation, maintenance of sexual reproduction, flexibility during development, role in immunologic escape of fetus, dominance modification
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What is cmpd heterozygosity?
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2 heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state. (eg connexin 26; AR deafness)
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What an example of triallelic inheritance?
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Bardet-Biedl Syndrome; mental retardation, pigmentary retinopathy, polydactyly. Obesity, hypogenitalism
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