Principles of Genetic Inheritance Flashcards
What is a chromatid
one of two identical copies of chromosome
What is a homologous chromosome?
a pair of chromosomes, almost the exact same, with order of the 4 loci being the same
What is the difference between metacentric, submetacentric and acrocentric in autosomes?
Meta= centromere in middle of chromosome
Sub=centromere off from the middle
Acrocentric= one side has little to know information
What is the karyotype?
An entire set of chromosomes, 46 in each diploid cells
How do you determine the sex of a karyotype?
XX is female
XY is male
What is lyonization (females)?
it is the inactivation of X, inactivated randomly, condensing the domain into a Barr body
What is mosaicism and examples?
A condition in which cells from a patient have different genotypes and karyotypes. EX: down syndrome 46XX/47XX, Klinefelter syndrome 46XY/47XXY, Turner syndrome 46XX/45XO
What is homologous recombination?
Where crossover exchange occurs and information from one chromosome is switched with info from another in meiosis
What are important steps of mitosis and what is the product?
Interphase is where chromosomes are duplicated
One copy of each chromosome and half of cyotplasm split between two daughter cells.
Results in 2 identical diploid cells
Differences between meiosis 1 and 2?
Meiosis 1 starts with diploid cells (homologs separated). Meiosis 2 starts with haploid cells and makes 4 gametes (chromatids separated)
What are some mitotic errors?
polyploidy:extra set of chromosomes
Aneuploidy: cells missing or have addition chromosomes (trisomy/monosomy)
What is nondisjunction and what does it form?
Nondisjunction occurs when homologous pair or single pair does not get separated, causing mono/trisomy
What are translocations?
Where non-homologous chromosomes exchange genetic material, either in reciprical or robertsonian
What is Klinefelter Syndrome?
a form of nondisjunction which leaves karyotypes with 47XXY
What is Turner syndrome?
a karytype for a female with 45XO, leads to lack of puberty, ovarian issues, normal intelligence
What is Trisomy 21?
Autosomal trisomy, 47XX+21, downsyndrome, due to translocation (robersonian) or age of mom
What is trisomy 13?
Patau syndrome, 47XX+13,
What is trisomy 18?
Edwards syndrome, 47XX+18
What is genomic imprinting?
gene silencing by methylation near 5’ end
What does it mean to be paternally imprinted, maternally?
Paternally imprinted (30 genes like this) means the paternal gene will be silenced and express the maternal gene, and vice versa
What is Prader-Willi/Angelman Syndromes?
PW deletion of a region on paternal chrom 15, resulting in obesity, small hands and feel, shortness
Angel: Deletion of region on maternal chrom 15, resulting in severe intellect disabilities, seizures and ataxic gait
What is uniparental disomy?
Related to nondisjunction and genomic imprinting: if 2 chromos are inherited from same parent (uniparental disomy) they will have parent specific imprinting
Difference between genotype and phenotype?
Geno: inidividuals genetic makeup
Pheno: physical presentation
Autosomal dominant inheritance?
One allele of gene need for expression. If unaffected cannot transmit the trait,
50% reccurent risk (Aa)
Autosomal recessive inheritance?
2 alleles of gene needed for expression of trait. skips generations, 25% or less reccurent risk (aa)
What is consanguinity and how does it affect autosomal recessive inheritances?
It is first cousin mating which cause an increase in expression of trait
What is X-linked recessive and example?
disease is on X, males hemizygous, females hetero or homozygous.
Females give to all sons, 50 daughters
All daughters of affected males are heterozygous carriers
EX: Duchenne Muscular Dystrophy
what is X-linked dominant (rare) and example?
Males w disease transmits to 100% females. Females to 50% of offspring.
EX: hypophosphatemia
What is reduced penetrance?
The frequency a gene manifests itself is called penetrance. So if phenotype occurs in 90% of individuals who have the defect, 90% penetrance (reduced from 100)
What is variable expressivity?
Describes the range of phenotypes that vary between individuals with a specific genotype EX: neurofibromatosis presents in many different shapes and colors
What is locus of heterogeneity?
a single disorder or trait cause by mutations in genes at different chromosomal loci EX:Osteogenesis imperfecta
Difference between gene and genotype frequencies?
Gene: specify the proportions of each allele in a population
Genotype: specify the proportions of each genotype in a population
What is the hardy weinberg principle?
p^2 + 2pq + q^2=1
Difference between nuclear and mtDNA?
Nuclear is in nucleus and has 2 copies per cell
mtDNA in mitochondria and has 100-1000 copies per cell, does not contain introns, inherited through maternal line
For a mitochondrial disease to show, what needs to happen?
A threshold needs to be met, eg: 60% of mitochondria need to be diseased to show symptoms (MELAS)
What increases recurrence risk?
more than one family member is affected
disease in proband, increases
environmental factors
What is multifactorial inheritance?
is polygenic (many genes), environmental factors
