Lecture 1: Intro to Genetics Flashcards
When Mendel crossed two pure line traits what were his findings?
he found that only one trait was expressed in the offspring
When is a dominant trait expressed?
can be expressed if only one copy of a gene is present
When is a recessive trait expressed?
trait is only expressed when both copies of a gene are present
What is the law of segregation?
dominant and recessive traits exist and are passed on from parent to offspring
What is the law of independent assortment?
traits are passed independently of other traits from parent to offspring
What is genotype?
an individuals collection of genes or can reference to two particular alleles that code for a gene -> genotype determines phenotype
What is phenotype?
the observed trait or set of traits that is created from your genetic makeup
What is penetrance?
disease is expressed in 100% of people with a particular genotype; incomplete or complete
Briefly describe the structure of DNA.
a double stranded helix; hydrogen bonds connect the two strands; there are four base pairs or nucleotides present; adenine, thymine, guanine, and cytosine; adenine pairs with thymine and is connected by two hydrogen bonds; cytosine pairs with guanine and is connected by three hydrogen bonds; the 5’ end has a phosphate group and the 3’ end has a hydroxyl group
What is the significance of the promoter region?
during transcription it is the region where RNA polymerase binds to a strand of DNA after unzipping the double helix
How is a chromosome formed?
genes are arranged in a complex called a nucleosome which is composed of DNA and histone and then nucleosomes are linked together to form chromatin which Is then further condensed to form a chromosome
What is the locus?
location of a particular gene on a chromosome
What is an allele?
a homologous copy of a gene… humans have two sets of each gene and one copy on each chromosome
What are the different kinds of mutations?
germinal which occurs during formation of an egg or sperm; somatic which occurs after conception; chromosomal aberration which is an alteration in the number or the physical structure of a chromosome
What are the three types of mutations that lead to an abnormal number of chromosomes?
monosomy- only one member of chromosome pair is present
trisomy- three chromosomes are present
polysomy- one chromosome is present 4 or more times
What is the most common trisomy?
down syndrome trisomy 21 which occurs 1 in 800 births
What are the presentations of a baby with trisomy 21?
cardiac defects, intestinal malformations, vision abnormalities, hearing loss, recurrent respiratory infections, memory loss with an increased risk of Alzheimer’ at an early age
What are the common characteristics of down syndrome?
decreased muscle tone. enlarged and protruding tongue, small nose, upward slant of eyes, abnormally shaped ears, deep palmer crease, hyperflexibility, extra space between first and second toe
XXY genotype
Klinefelter Syndrome
What is the most common genetic abnormality associated with primary hypergonadism?
Klinefelter Syndrome
What are the consequences of Klinefelter Syndrome?
males have small external genitalia and testes, 50% will develop breasts, usually sterile and impaired spermatogenesis, elevated levels of FSH and LH, decreased serum testosterone, abnormal arm and leg length, increased risk for breast cancer and pulmonary disease, may have impaired social skills including ADHD and impaired judgment, impaired higher language skills, increased risk of Non Hodgkin’s Lymphoma, leg ulcers, diabetes, lupus
XO genotype
turner syndrome
What is the female appearance in Turner Syndrome?
short wide chest, usually sterile, low estrogen, small breasts, normal mental development, neck skin folds, webbing of the neck
What are the consequences of Turner syndrome?
hearing loss, hypothyroidism, autoimmune thyroiditis, elevated liver enzymes, primary amenorrhea, osteoporosis, increased fractures, renal structure abnormalities, vision and ocular abnormalities, autoimmune disease, diabetes, hyperlipidemia, hypertension, cardiac structural abnormalities, aortic dissection, increased CV mortality
When taking a family history who should be included?
all first degree relatives and should include parents, siblings, and offspring
What is the pedigree pattern in autosomal dominant inheritance?
multiple generations are affected and in a vertical pattern
What is autosomal dominant inheritance?
mutation in a SINGLE allele of autosome is enough to cause disease or abnormal phenotype… only one affected parent is necessary for child to be affected
What is the chance of each child having an abnormal phenotype with autosomal dominant inheritance?
50%
What are some examples of autosomal dominant diseases?
Huntington’s Disease, Hypercholesterolemia, Neurofibromatosis Type 1, Polycystic Kidney Disease
What is autosomal recessive inheritance?
mutation in which two copies of the allele of autosome are required to manifest the abnormal phenotype; horizontal patter in the pedigree
Who must be a carrier in order for offspring to manifest the trait in autosomal recessive inheritance?
both parents must be carriers in order for offspring to manifest the trait
What is the chance for offspring to be affected or a carrier in autosomal recessive inheritance?
offspring have a 25% chance of being affected… 50% chance of being a carrier
What are some examples of autosomal recessive diseases?
Phenylketonuria, Sickle cell anemia, cystic fibrosus, thalassemia
Are males and females hemizygous, heterozygous or homozygous for the mutant alleles in x-linked inheritance?
males are hemizygous- XY
and females are either heterozygous or homozygous- Xx or xx or XX
What are some examples of X-linked dominant disease?
Hypophosphatemic rickets
Rett’s syndrome
How many copies of mutant allele are required to produce X-linked recessive disease in males and females?
two copies of mutant allele are required to produce the disease in females but only one copy is required in males to produce the disease
What are some examples of x-linked recessive diseases?
hemophilia A, duchenne’s muscular dystrophy, red-green color blindness
What is mitochondrial inheritance?
transmission of mitochondrial DNA is maternal; mother passes her mitochondrial DNA including mutant DNA to all of her children, male or female
What are some examples of mitochondrial mutations?
cyclic vomitting syndrome, myoclonic epilepsy with red-ragged fibers, nonsyndromic deafness, Leigh syndrome
