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define dysmorphology
the study of human congenital malformations and birth defects
dysmorphology combines knowledge of:
genetic principles
developmental mechanisms
natural history of congenital abnormalities
what are common dysmorphologies related to Down Syndrome?
upslanting palpebral fissures
flattened nasal bridge
brushfield spots
low-set, small, folded ears
short neck
epicanthal folds
what is the dysmorphology term for a child’s head being either to large or small
microcephaly and macrocephaly
define hypertelorism
eyes are too far apart
define hypotelorism
eyes are too close together
define telecanthus
the inner corners of the eye are displaced laterally
define epicanthal folds
folds of skin overlapping the inner canthi
define blepharophimosis
small eye openings
define prognathia
jaw protrudes out
define retrogneathia
jaw retracts
define micrognathia
small jaw
define polydactyly
extra digits
define syndactyly
fused digits, deficiencies, abnormal creases
define brachydactyly
short digits
define arachnodactyly
long digits
define oligodactyly
missing digits
what enzyme converts testosterone to dihydrotestosterone
5a-reductase
what type of inheritance does Guevedoces display
autosomal recessive
Guevedoces is primarily what type of mutation?
missense
Pseudoautosomal regions (PAR1 and PAR2) make up __-__% of the chromosome
5-10%
What is the other 95% (not PAR1 and PAR2) of the male chromosome referred to as
Male Specific Region
what does the SRY gene code for
transcription factor protein - stimulates male development and sends signals to gonads to degenerate female structures
define pronucleus
the sperm/egg nucleus after sperm has entered the ovum at fertilization but before fusion of the pronuclei
what are sex-limited traits
traits that affect a structure or function occuring only in one sex - may be autosomal or X-linked
examples of sex limited traits
beard growth
milk production
preeclampsia in pregnancy
what are sex-influenced traits
allele is dominant in one sex but recessive in the other - difference in expression can be caused by hormonal differences between sexes
sex-influenced trait examples
pattern baldness in humans - heterozygous male is bald, heterozygous female is not
what is the paternal age effect?
increased risk of health disorders in children with older fathers
examples of disorders that display the paternal age effect:
achondroplasia
crouzan syndrome
multiple endocrine neoplasia 2
pfeiffer syndrome
thanatophoric dysplasia
how many possible combinations of maternal chromosomes via independent assortment
2²³ = ~8,000,000
What is the MHC
Major Histocompatibility Complex - codes for proteins to help the immune system identify foreign antigens
what is another name for the MHC
HLA region - Human Leukocyte Antigen
where is the MHC located
Located on the short arm of chromosome 6
functions of the MHC
presentation of intracellular and extracellular pathogens
inflammation
neural development
potentially related to mate selection
environmental factor responses
What are the three regions of MHC called
Class I, Class II, Class III
Describe Class I region of MHC
expressed on nearly all nucleated cells
presenting endogenous (intracellular) peptides to CD8+ T cells
genes: HLA-A, HLA-B, HLA-C, etc
CD8 cell function
directly kill infected immune cells
describe class II region genes of MHC
expressed on antigen presenting cells (APCs)
presenting exogenous (extracellular) peptides to CD4+ T cells
adaptive immunity
genes: HLA-DP, HLA-DQ (two letters = class 2)
describe class III region genes of MHC
expression affects inflammation and immunity
complement proteins and cytokines
supports both innate and adaptive immunity
genes: Complement component 4 (C4), TNF-a/b, etc
____ genes are the most polymorphic genes in the human genome
MHC
what does high allelic diversity allow for
better immune recognition but complicates transplantation compatibility
what is the most polymorphic gene in the human genome
HLA-B
True/false: certain MHC alleles may confer resistance or susceptibility to autoimmune responses
true
which type of selection maintains MHC diversity and why?
balancing selection - prevents any single allele from becoming fixed or lost in a population
_____ genotypes can present a wider variety of pathogen-derived antigens
heterozygous - harder for antigens to escape immune detection
does infectious disease promote or inhibit HLA diversity
promote
what is a haplotype
a set of genes or genetic markers that are inherited together from one parent
siblings have a ___% chance of a full HLA match
25%
mismatched HLA alleles can lead to ____________ or organ rejection
graft-versus-host-disease - transplanted immune cells (graft) attack the recipient’s (host) healthy tissues
what is linkage disequilibrium
the nonrandom association of alleles at different loci in a population
define cytogenetics
the study of chromosomes and their abnormalities
Benefits of using Fluorescent in situ hybridization
sequence and chromosome specific places in DNA
simultaneous assessment of multiple genetic targets in an intact cell
relatively easy interpretation
easy to perform
short time-to-result
quantitates genetic changes cell-by-cell
abnormal chromosomes account for at least __% of spontaneous abortions
50%
nondisjunction during meiosis I results in
both homologs in one gamete
nondisjunction during Meiosis II results in
both sister chromatids in one gamete
frequently seen trisomies:
21, 18, 13
Describe Trisomy 18
Edward’s Syndrome
commonly do not survive
mental and physical disabilities
oddly clenched fists
Describe Trisomy 13
Patau Syndrome
very rare and generally do not survive past 6 months
serious mental and physical disabilites
eye fusion
name ways you can diagnose aneuploidies
standard cytogenic
QF-PCR (quantitative fluorescenting)
NIPT (noninvasive prenatal testing)
serum and ultrasound screening
Describe Klinefelter syndrome
85% nondisjunction
XXY
common cause of male infertility
incomplete sexual development, rudimentary testes and prostate, long limbs, large hands and feet, breast tissue development
Describe Jacob’s Syndrome
XYY aneuploidy
96% are phenotypically normal
modest phenotypes - great height, acne, speech and reading disabilities
describe XXYY syndrome
arises due to unusual oocyte and sperm
more severe behavioral problems than Klinefelter’s - OCD, learning disabilities
infertile and treated with testosterone
Describe Turner Syndrome
XO
99% of fetuses die in utero
features: short stature, webbing at the back of neck, incomplete sexual development, impaired hearing
individuals who are mosaics may have children
Triplo-X Syndrome
few modest effects on phenotype
tallness, menstrual irregularities, and slight impact on intelligence
X inactivation of two X chromosomes occurs
Reciprocal Translations
two non-homologous chromosomes exchange parts
usually healthy because they have the normal amount of genetic material
Robertsonian Translocation
two nonhomologous, acrocentric chromosomes break at the centromere and the long arms fuse
is nondisjuction more common in males or females
females
what do mitochondrial genomes code for
polypeptides required for mitochondrial respiratory chain
what type of diseases result from mitochondrial mutations
monogenic disorders that affect the nervous system, muscles, heart, and endocrine organs
mutations with milder contribution to common complex traits and late-onset disorders
does mtDNA contain introns?
no
is there recombination in mtDNA
no
what makes mtDNA easily mutable
high exposure to free radicals
how many copies of DNA do each mitochondrion contain
2-10
functions of the mitochondria
cellular metabolism
intracellular calcium signalling
biogenesis of iron-sulfur clusters
apoptotic cell death
define heteroplasmy
mosaicism for mitochondrial DNA variants, usually within a single cell
levels of heteroplasmy can vary:
between cells in the same tissue or organ
from organ to organ in the same person
between individuals in the same family
what is leber optical atrophy and what can it be the result of
impaired vision - mitochondrial disorders
describe Leber Hereditary Optic Neuropathy (LHON)
painless, progressive loss of central vision - degeneration of retinal ganglion cells and their axons, leading to acute loss of central vision
missense mutations - low penetrance with males more likely to become blind
Describe myoclonic epilepsy with ragged red fibers (MERRF)
tRNA mutation
progressive epilepsy and dementia, onset late childhood-adulthood
are mtDNA point mutations or mtDNA deletions inherited
point mutations
are mtDNA point mutations or mtDNA deletions homoplasmic
point mutations
describe Friedreich’s Ataxia
triplet/trinucleotide repeat disorder
results in cell death, in particular of neurons, heart muscle, and beta cells in pancreas
5 hardy weinburg assumptions
infinite number of individuals in the population
random mating
no new mutations
no migration
no natural selection
what is genetic load
collection of recessive deleterious alleles in a population
describe population bottlenecks
occurs when a large population is drastically reduced in size - Ashkenazi Jews
Founder Effect
all individuals in a population with a certain illlness have the same mutation - BRCA1 breast cancer among Ashkenazi Jewish people
describe balanced polymorphism
harmful recessive alleles are replaced by new mutation, and persistence in heterozygotes - sickle cell