Principles Of Genetic Inheritance Flashcards
Each gene occupies a specific place, or _______
Locus
___________ = one of two identical copies of a chromosome
Chromatid
____________ = connects identical sister chromatids
Centromere
_____________ = region at the end of chromosome for stability
Telomere
Typical human diploid cell has 23 pairs of chromosomes. 22 pairs are called _______, the 23rd pair is _____ or _____
Autosomes
XX or XY
Human ________cells are diploid and differentiated
Somatic
________are haploid cells
Gametes
______ Cells are undifferentiated and can divide into 2 diploid cells
Stem
___________ chromosomes refer to pairs of chromosomes, thus there are 2 copies of each gene with the order of the 4 loci being identical
Homologous
Entire set of patient’s chromosomes represents their ___________
Karyotype
46 chromosomes in a karyotype are in each of the patient’s diploid cells, unless ___________ occurs, which is a condition in which patients have different genotypes
Mosaicism
For Chr16p12.2 -
Identify chromosome, region, band, sub-band, and arm
Chr = 16 Region = 1 Band = 2 Sub-band = 0.2 Arm = p arm
What is a natural form of mosaicism?
Lyonization - or X-inactivation. The choice of which X chromosome will be inactivated is random
What is the genotype of Downs syndrome?
Some 46XX, some 47XX + 21
What is the genotype of Klinefelter syndrome?
Some 46XY; some 47XXY
What is the genotype for Turner syndrome?
Some 46XX, some 45XO
Meiosis reduces the total number of chromosomes by half, producing four gametes. In meiosis, __________ ________ produces new combinations of genes
Homologous recombination
______________ is the failure of one or more pairs of homologous chromosomes, or sister chromatids, to separate normally during division.
What does this cause?
Non-disjunction
Causes spontaneous abortion and mental retardation
How does meiotic cell division produce haploid cells?
One round of DNA replication + 2 rounds nuclear divisions
____________ are chromosomes common in both genders (one from each parent)
Autosomes
In what 2 ways does meiosis generate genetic diversity?
Random segregation of homologs
Crossing over
____________ refers to cells with an abnormal chromosome number
Aneuploid
What is the most common cause of mental retardation?
Trisomy 21 (Downs)
In 90% of trisomy 21 patients, the addition chromosome is ____________
70% occurs during __________
30% occurs during __________
Maternal
1
2
__________ refers to cells with the normal number of chromosomes
Euploid
What type of Trisomy 21 is characterized by the genotype 47, XX + 21?
Translocation type - due to Robertsonian translocation
What is the Robertsonian Translocation?
Long q arm 21 fuses to long q arm 14, resulting in acrocentric chromosomes
What type of Trisomy 21 has the genotype 46, XX, der(14;21)(q10; q10), +21?
Mosaic type
What is the result of methylation on genes?
Downregulation
Methylated genes are considered to be __________, which can be passed on from generation to generation
Imprinted
What is the result of two chromosomes from the same parent that have parent-specific imprinting?
No gene product
Two different conditions occur with the exact same deletion on chromosome 15.
What condition does the child develop if the paternal chromosome is deleted?
Prader Willi syndrome
Two different conditions occur with the exact same deletion on chromosome 15.
What condition does the child develop if the maternal chromosome is deleted?
Angelman syndrome
Gregor Mendel is the ‘father of modern genetics’. What 3 laws did he come up with?
Genes are discrete units
Law of segregation
Law of independent assortment
What are the 2 broad types of genetic diseases?
Monogenic (single-gene)
Multifactorial
Dystrophin –> Duchenne Muscular Dystrophy
What is the genetic mechanism?
Loss of function
Oncogene –> cancer
What is the genetic mechanism?
Gain of function
B-globin –> sickle cell anemia
What is the genetic mechanism?
Protein alteration
Individuals with distinct genotypes can have a single phenotype, as is the case with ________ _________
Conversely, individuals with the same genotype can have multiple phenotypes, as is the case with _________
Cystic fibrosis
PKU
Why is it that PKU patients with the same genotype (PAH deficiency) have multiple phenotypes?
Some patients will be able to metabolize and excrete Phe more efficiently than others
Why is it that cystic fibrosis patients have distinct genotypes and only one phenotype?
Whether you have no CFTR proteins at all, or dysfunction of your existing CFTR proteins, you will have the same resulting symptoms
When looking at pedigrees, the ________ refers to the first diagnosed person in the pedigree.
Proband
What type of inheritance is characterized by only 1 allele needed for expression, so only one parent was affected
Autosomal dominant inheritance
With autosomal dominant inheritance, unaffected individuals do not transmit the trait.
Males and females can transmit the trait to both males and females - (_______________)
Trait is expected in ________ generation
Recurrent risk is ________%
Autosomal
Every
50
Postaxial polydactyly is an example of what type of inherited disorder?
Autosomal dominant
What type of inheritance requires 2 copies of a gene to influence the phenotype?
Autosomal recessive
Tyrosinase-negative albinism is an example of what type of inherited disorder?
Autosomal recessive
What is the recurrent risk of autosomal recessive diseases?
25%
With autosomal recessive disease, occurence is more likely among individuals who engage in ___________ mating
Consanguinous
X-linked Recessive disorders:
Disease allele on X in males is termed ___________
Females can be __________ or ______________
Unaffected males do not transmit the trait
Females transmit to ____% of sons and _____% of daughters
Hemizygous
Heterozygous; homozygous
50; 50
If a male is a carrier of an x-linked recessive disorder, how many of his potential daughters will be heterozygous carriers?
All of them
Duchenne muscular dystrophy is an example of what type of inherited disorder?
X-linked recessive
Hypophosphatemia is what type of inherited disorder?
X-linked dominant
How do males and females compare in their ability to pass on an x-linked dominant trait?
Males with disease allele transmit the trait only to females with 100% transmission rate
Females with disease allele transmit the trait to both male and female offspring with 50% transmission rate
The frequency that a gene manifests itself is called _________
Penetrance
[with retinoblastoma, the phenotype occurs in 90% of individuals inheriting the gene defect, so 90% penetrance]
What type of inheritance is demonstrated by retinoblastoma?
Autosomal dominant
What is the term used to describe a range of phenotypes that vary between individuals with a specific genotype?
Variable expressivity
What is a disease example of variable expressivity?
Neurofibromatosis
People develop tumor like growths called neurofibromas - cafe-au-lait spots = pigmented areas that vary in their clinical presentation
Osteogenesis imperfecta may result from a mutation in either Chr 7 or Chr 17, this is an example of what concept of mendelian inheritance
Locus heterogeneity - a single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci
What principle specifies the relationship between gene frequencies and genotype frequencies?
Hardy-Weinberg principle
What type of inheritance is characterized by vertical transmission of phenotype, lack of skipped generations, roughly equal males and females affected, and father-son transmission may occur?
Autosomal dominant
What type of inheritance is characterized by clustering of disease phenotype among siblings, but not usually seen among parents or other ancestors, equal males and females affected, consanguinity may be present
Autosomal recessive
Traits in which variation is thought to be caused by the combined effects of multiple genes = _________
Polygenic
When environmental factors cause variation in the trait, the term __________ is used
Multifactorial
For diseases that do not follow the bell-curve distribution, there is an underlying ___________distribution. For multifactorial diseases that are either present or absent, it is thought that a ________________ must be crossed before the disease is expressed. Below that, the person appears normal.
Liability
Threshold of liability
Explain the concept of the threshold model as it relates to pyloric stenosis, which is 5x more common in males than females
Children of women with pyloric stenosis are more likely to be born with the condition - especially males
Children of affected males with pyloric stenosis are less likely to be born with the condition
The recurrence risk is ______ if more than one family member is affected
If the expression of disease in proband is more severe, the recurrence risk is ________
The recurrence risk is ______ if the proband is of the less commonly affected sex
The recurrence risk is usually _____ in more remotely related areas
Higher
Higher
Higher
Decreased
