Principles Of Genetic Inheritance Flashcards
Banding and nomenclature:
What does 17q11.2 mean
17th chromosome Q = longer arm 1 = closest band to the centromere 1 = band staining technique .2 = specific portion of band 1
When is a karyotype made
During metaphase of the M phase
After replication
Lionizations (X-inactivation)
The inactivation of one of the X chromosomes in females; performed randomly
Mosaicism
A condition in which cells from a patient have different genotypes an karytopes
Mosaicism and Turner’s syndrome
Some cells will have 46XX (normal) and some will have 45XO
Around 30% of turner’s syndrome cases demonstrate mosaicism
Mosaicism and Down’s syndrome
Some cells are 46XX (normal) and some are 47XX+21
Mosaicism and Klinefelter Syndrome
Some cells are 46XY (normal) and some are 47XXY
How do stem cells divide
They undergo mitosis, but divide asymmetrically, resulting in one stem cell and one daughter cell
Homologous recombiantion (crossing over)
Produces new combinations of genes; part of the maternal chromosome switches with its counterpart in the paternal chromosome, resulting in a recombination of genes
Two ways in which meiosis creates genetic diversity
- Random segregation of homologs
2. Cross-over exchange (homologous recombination)
Euploid
Cells with normal number of chromosomes
- haploid gametes and diploid somatic cells
Polyploidy
Presence of a complete set of extra chromosomes in a cell
- often seen in plants
Aneuploid
Cells with a missing or additional individual chromosomes
- monosomy and trisomy
Symptoms of Turner Syndrome
45, XO karyotype
Female
- short
- ovarian hypofunction/premature ovarian failure
- need hormone therapy for puberty
- infertility
- webbed neck (in 30% of cases)
- low hairline on neck
- cardiovascular defects
- normal intelligence ***
Symptoms of Klinefelter syndrome
47XXY
Male
- cognitive, social, behavioral, learning difficulties
- primary hypogonadism (low T)
- small/undescended testes
- tall
- infertility
- gynecomastia (male breasts)
Patients can also not show symptoms
Reciprocal translocation
An exchange of material between nonhomologous chromosomes
Robertsonian translocation
When the long arms of two acrocentric chromosomes are combined and the short arm is lost (typically)
Patau Syndrome
47XX+13
Severe developmental abnormalities
Most perinatal death within 1 week
Edwards Syndrome
47XX+18
Abnormal development
Most perinatal death within 1 year
Genomic Imprinting
Essentially gene silencing through methylation of 5’ region of the gene
Causes chromatin condensation
At least 100 human genes are known to be imprinted
- clustered together
~ 30 genes that are paternally imprinted and maternally expressed
~ 70 genes that are maternally imprinted and paternally expressed
What happens to imprints during meiosis in germ cells
They are erased and new ones are set
Prader-Willi syndrome
Deletion of PWS region/AS gene on paternal chromosome 15
- short
- hypotonia (weak muscle tone)
- small hands and feet
- obesity
- mild/moderate intellectual disability
Angelman Syndrome
Caused by a deletion in PWS region/AS gene on the maternal chromosome 15
- severe intellectual disabilities
- seizures
- ataxic gait
Uniparental disomy
When two chromosomes are inherited from the same parent, instead of one being inherited from the father and one from the mother
Caused by nondisjunction in mother or father, which will cause 1/3 of gametes to have two chromosomes of one parent and none of the other
Can cause Prader Willi and Angelman
Law of segregation in Mendelian genetics
Allele pairs separate during gamete formation and randomly unite during fertilization
Law of independent assortment in Mendelian genetics
Individual hereditary factors assort independently during gamete formation
Does cystic fibrosis stem from multiple genotypes or multiple phenotypes
Distinct genotypes, single phenotype