Intro Flashcards
How many copies of mitochodnrial DNA is in each cell>
Exists in thousands of copeis in each cell, so genes packed into cell cytoplasm
Is mtDNA exon or intron
purely exon
Homoplastic vs heteroplastic
Homospalistic indivdiuals- show genetically indetnical mtDNA in very cell
Hteroplastic individuals have a mix of genetically different mtDNA in their cells
What is the cuase of mutifactoral (polygenic) disorders?
from interactions of genes at multiple loci and also may be influenced by environemtnal factors, sucha s mutagenic chemcials
Multfactorial genetic disorders do not follow Mendelain inhertiance
COMPLEX INHERITANCE
genetic imprinting
if expression of a disease phenotype depends upon which parent passed along teh mutation
i.e. Huntington’s disease has an earlier onset when inherited from the father compared to the mother
Penetrance
probability that a person witha particualr mutated gene will exhibit a phenotype (disease). Some alleles may show reduceds or incompelte penetrance.
Indivuals carrign that mutated gene have a reduced pehnotype
complete penetrance
trait will be detected in everyone that has the mutation
Expressivity
the range of phyiscal manifestions of the phenotype among indivuals with the same disease-causing genotype
Age-dependent onset and modification by other genes in teh indivdual’s genome will also modify the character of genetic disorders
What is a proband
the family member who brings the disorder to medical geneticist, if he/she is affected by the diseases
Consultant
an unaffected individual who may bring the disorder to the attention of a medical geneticist is known as a consultant
What does it mean to be consanguineous
coupels who have more than one ancestor in common
What are characterisitcs of Autosomal Dominant inheritance
- phenotype detected in every generation, each affected person has an affected parent
- Any child of an affected parent has 1 in 2 inheritance risk (50%)
- Phenotypically normal family members do not transmit the mutant phenotype to their children
- both genders are equally likely to transmit the phenotype to children of eithe rsex
- A signifiant proportion of isoalted cases may be due to new mutations
Characteristics of autosomal Recessive inheritnace
- inherited through BOTH parents, who are asymptomatic (blue bull’s eyes)
- Disease occurs only in homozygotess- no normal gene copy compensates for mutatn allele
- Parents of an affected child are asymptomatic carriers of the mutant alleles
- The risk for each proband sib is 1 in 4
- Granparents (second degree relations; shaded gray with bulls’ eye notation) must hve possessed one copy of mutant allel that was passed on
Characteristics of X-linked recessive inheritance
- Phenotype is much higher in males than in females
- heterozygous females are usually not affected, but some may express the condition with variable severity based upon X inactivation
- Mutant gene is transmitted from affected man to his daughters (obligate carriers); any of his grandsons has 50% chance of inheriting the mutations
- Mutant allel may be transmitted through a series of carrier females, and teh affected males in a kindred are related through the females
- Never transmitted directly from father to son
What clinical significance is associated with deletions
mental impairment
structural malformations
Cri-du Chat syndrome
What is Mosaicism?
chromosomal aberration occurring after fertilization that produces a mixture of normal and abnormal cells
Cells may be somatic or germ cells
Mosaicism is not transferred to offspring unless it occurs in the germ line cells
When is mosaicism transferred to offspring?
only when it occurs in the germ line cells
What is a chimera>
individuals with contributions from more than one fertilized ovum
What stage of mitosis are cells in when a “chormosome spread” is made from WBC
Metaphase
What is a karyotype
sum of all chromosome information
What are the two arms of a chromosome called?
short arm = p arm
long arm = q arm
position of the primary constriction of the chromosome (another name for centromere) defines whether the chromosome is meacentraic or acrocentenric
Difference between metacentric vs acrocentric
Metacentric (2 substantial arms)
Acrocentric (one very tiney arm and one which contains almost all DNA)
Which chromosomes are acrocentric?
13, 14, 15, 21, 22
What is mosaicism?
non-disjunction can occur during mitosis during early embryogenesis
This yields a mosaic embryo, which is defined as arising from a single zygote and has more than one genotype
Mitotic non-disjunction may be observed b/c it “rescuses an original trisomic zygotic (which is suually lethal) by providing a normal cell line
How can you determine the fraction of cells having each genotype?
variable, reflecting how early during embryogeneiss the mosaicism originated
Why are females considered to be mosiacis
all normal females have roughly equal popluations of two genetically different cell types and are therefore a type of mosaic.
in roughly half the cells, paternal X chromosome has been inactivatd, and in the other half the maternal X chromosome is inactive
What is a chimera
Composed of more than two cell-lines that originated form different zygotes, e.g. fraternal twins fused into one zygote
interspecies chimeras have also been produced experimentally