Genes and Genetic Diseases

Euploidy

23 pairs of chromosomes or 46 chromosomes(normal)

Autosomal Chromosomes

pairs 1 through 22

Sex Chromosomes

-pair 23 -either XX or XY

Histone

any group of basic proteins found in chromatin

Chromatin

-complex of DNA and protein found in eukaryotic cells -functions to package long DNA molecules into more condense structures

Chromosome

-thread like structure made of protein and a single molecule of DNA -functions to carry genetic information from cell to cell

Gene

sequence of nucleotides in DNA/RNA and is the basic unit of inheritance

Locus

specific, fixed position on a chromosome where a particular gene/genetic marker is located

Alleles

different versions of DNA sequence at a given genomic location

Genotype

the genetic makeup of an individual cell/organism

Phenotype

observable characteristics of an individual resulting from the interaction between genotype and environmental factors

Homozygous

-two of the same alleles -HH or hh

Heterozygous

-two different alleles -Hh

Dominant Gene

requires only one allele to express phenotype

Recessive Gene

-requires two alleles to express phenotype -often masked

Codominant

-both alleles are expressed -AB blood type

Carrier

-possesses defective gene but does not show symptoms of disease -Hh

Centromere

point of the chromosome to which the spindle attaches during cell division

Short Arm

top half of chromosome(p)

Long Arm

bottom half of chromosome(q)

Chromosomal Abberations

entire chromosome is defective

Single Gene Disorder

specific gene on a chromosome is affected

Multifactoral

genetic and environmental factors

Aneuploidy

-abnormal number of chromosomes -can be more or less

Trisomy

-3 chromosomes -CAN SURVIVE

Monosomy

-1 chromosome -LETHAL

Nondisjunction

-cause aneuploidy -failure of chromosome/sister chromatids to separate during cell division

Autosomal Aneuploidy

Trisomy 21(Down Syndrome)

Sex Chromosome Aneuploidy

-Turner Syndrome(X__) -Klinefelter Syndrome(XXY or XXXY)

Trisomy 21 Risk Factor

mother over 35 years old

Trisomy 21 Manifestaions

-epicanthal fold -congenital heart disease -poor muscle tone -intellectual deficiency -low nasal bridge -protruding tongue -low-set ears -flat occiput -and more

Turner Syndrome

female with one X chromosome(genotype)

Turner Syndrome Manifestations

-underdeveloped ovaries(sterile) -short stature(not midget) -WEBBING OF NECK -edema -underdeveloped breasts/wide nipples -high number of aborted fetuses(usually how someone is diagnosed)

Klinefelter Syndrome

-XXY or XXXY -more X=more abnormalities

Klinefelter Syndrome Manifestations

-male appearance -gynecomastia(breast development) -small testes(usually sterile) -sparse body hair -long limbs -wide hips -lack facial hair -tall stature

Pedigree Table

tool for studying genetic disorders within a family

Single Gene Diseases

-Autosomal Dominant(only 1 allele) -Autosomal Recessive(2 alleles/both parents) -X-linked recessive(more prominent in men, only one X)

Recurrence Risk

probability that an individual WILL DEVELOP a genetic disease

Penetrance

probability of a gene or trait being expressed, GENOTYPE

Expressivity

refers to variation in the phenotypic expression, PHENOTYPE

Autosomal Dominant Inheritance

-delayed lethal phenotype -no carrier -does not skip generations -50% recurrence risk of getting the disease if one parent has the allele

Autosomal Dominant Diseases

-Huntington's Disease -Marfan Syndrome -Neurofibromatosis -Von Willebrand's disease

Huntington's Disease

-chromosome 4(hunt) -neurodegenerative

Marfan Syndrome

connective tissue abnormalities

Neurofibromatosis

-chromosome 17 -neurofibromas -cafe au lait spots

Von Willebrand's Disease

slowed clotting process

Autosomal Recessive Inheritance

-carriers(Hh) -commonly caused by consanguinity(incest) -commonly die at a young age -recurrence risk 25%

Autosomal Recessive Disorders

-cystic fibrosis -sickle cell anemia -phenylketonuria/PKU(lacks PAH) -Tay-Sachs disease(lacks hexosaminidase, chromosome 15)

Cystic Fibrosis

-Most common in white people -defective CFTR gene -affects lungs and digestive tract(pancreas) -maldigestion due to pancreas not able to secrete mucus containing enzymes

Sickle Cell Disease

-common in African Americans -replaces glutamic acid with valine -RBC sickle under conditions that cause low oxygen levels

Sickle Cell Disease Manifestations

-CVA -paralysis -death -retinopathy/blindness -hemorrhage -avascular necrosis(shoulder,hip) -hepatomegaly -splenomegaly -gallstones -hematuria -priaprism -osteomyelitis -chronic ulcers -anemia

X-linked Recessive Inheritance

-males affected -females carriers -consanguinity(incest) -males give to female offspring not male -sons of female carriers 50% recurrence

X-linked Recessive Disorders

-Hemophilia -Muscular Dystrophy -Red/green color blind -Alport Syndrome

Multifactoral Inheritance

genetic influence and environmental factors

Multifactoral Inheritance Examples

-cleft palate -congenital hip dislocation -congenital heart disease -type 2 diabetes mellitus

Timing of Diagnostic Test

-prior to conception -during pregnancy -in newborns

Testing Recommended

-family history -previous child with abnormalities -woman over 35 y/o -ethnic group with high risk specific disease

Alpha-fetoprotein Testing

if levels are low, baby will have trisomy 21

Excreted Metabolities Test

for PKU in neonatal