Principles of Genetic Inheritance Flashcards
Lyonization
Also called x-inactivation. When one x chromosome is randomly inactivated in a cell
Translocations
non-homologous chromosomes will exchange genetic material- two types reciprocal or Robertsonian
Robertsonian Translocation
Long arm of two acrocentric chromosomes combined, short arm typically is lost
EX- chrom 14 and chrom 21- the long arms of 14 and 21 will combine and the short arm will be lost.
Reciprocal translocation
exchange of material between non homologous chromosomes
Turner Syndrome
Genotype- 45, XO- has normal intelligence but will be short in stature, be infertile, 30% webbed neck, low hairline, most will not go through puberty without hormone therapy
Klinefelter Syndrome
Genotype- 47, XXY- Some will have little to no sx. Primary hypogonadism (low T), tall in stature, infertile. Can be worse if there are more X chroms involved.
Downs Syndrome
Genotype- 47 XX +21- Most common trisomy. Greater risk with older women.
Patau Syndrome
Genotype- 47 XX +13- Severe developmental abnormalities and death results in about one week
Edwards Syndrome
Genotype- 47 XX +18- Abnormal development, resulting in death about one year
How many genes are known to be maternally imprinted?
70
How many genes are known to be paternally imprinted?
30
Genomic imprinting
Gene silencing through 5’ methylation of gene sequence- chromatin condensed and inactive. Can be inherited from parent to offspring
Prader Willi- syndrome
Deletion of PWS and AS genes from paternal chromosome- result in short stature, hypotonia, small hands/feet, obesity and slight intelligence deficits
Angelman Syndrome
Deletion of PWS and AS genes from the maternal chromosome- result in severe intellectual disability, seizures and ataxia
Penetrance
frequency a gene manifest the phenotype
Expressivity
Range of phenotypes given a particular genotype
What is the difference in penetrance and expressivity?
Penetrance is either the phenotype is present or not while expressivity is a range of phenotypes.
Locus heterogenity
single disorder, trait or pattern of traits that are caused by mutations of genes at different chromosome loci
Mitochondria DNA
comes from the maternal line only- mutation rate is much higher since there are no repair mechanisms and higher damage present from O2 radicals
Leber’s hereditary optic neuropathy
mitochondrial disorder- degeneration of retinal ganglion cells
Mitochondrial encephalomyopathy, lactic acidosis, and
stroke-like episodes
Mitochondria disorder
Polygenic
variations in phenotype are the result of many different genes working in tandem
multifactoral inheritance
When the environment and multiple genes effect the outcome of the phenotype
Threshold of liability
Some disorders that are multifactorial have a line that means the disorder will be expressed or not.
What factors make recurrence of a multifactoral disorder more likely in a population?
1: if more than one member is affected
2: If expression in the proband is more severe
3: if the proband is of the less commonly affected sex
4: more closely related to the proband
