Genetics intro Flashcards
Who was the Australian monk and founder of modern genetics?
Gregor Mendel
Before Gregor Mendel, how did scientists think traits were inherited?
by blending of parents’ traits
What were the results of the DNA analysis on Gregor Mendel when his body was exhumed?
-very large brain
-neurologic disease genes identified
What did Gregor Mendel experiment with?
pea plants
What are the names of Mendel’s Laws?
- law of segregation
- law of independent assortment
- law of dominance
What is the law of segregation?
each person has two alleles for each gene and only one is contributed to a gamete in a random manner with equal frequency
What is the law of independent assortment?
alleles for different genes are sorted into gametes independently of each other, therefor one allele of a gene does not affect a different allele of a different gene
What is the law of dominance?
in a heterozygote, one trait will conceal the other and the presence of a dominant allele will conceal the trait of the recessive allele
What is it called when alleles of a gene are identical (AA or aa)?
homozygous
What is it called when alleles of a gene are different (Aa)?
heterozygous
What is the location of a gene on a chromosome called?
locus
What is the individuals collection of genes, or can reference to two alleles that code for a gene (AA, Aa, aa)?
genotype
What is the observable trait or set of traits that is created from your genetic makeup–hair color, flower color, wrinkled seeds?
phenotype
Genotype determines ___________
phenotype
What is is called when a disease is expressed in 100% of people with a particular genotype, incomplete or complete?
penetrance
most diseases are _______
polygenic
What does it mean when it is said that most diseases are polygenic?
several or many alleles of several genes are interacting
How many chromosomes do humans have?
46 chromosomes
-22 pairs of autosomes
-1 par of sex chromosomes
During cell division, what can lead to an abnormal number of chromosomes?
nondisjunction
What is nondisjuction?
failure of chromosome pairs to separate
What are examples of nondisjunction that occurs during cell division?
monosomy
trisomy
polysomy
What is it called when only one member of chromosome pair is present?
monosomy
What is it called when three chromosomes are present?
trisomy
What is it called when one chromosome is present 4 or more times?
polysomy
What can occur in a chromosomal region that can cause no or severe changes in a phenotype?
deletions and inversions
What is the most common trisomy?
down syndrome (trisomy 21)
The risk of having a child with down syndrome increases with _______
maternal age
Women who become pregnant at 35 or older are considered high-risk for what?
down syndrome and other malformations due to increased age
What tests are beneficial for diagnosis of down syndrome during pregnancy?
labs and ultrasounds
What are these facial characteristics associated with?
-flat facial features
-upward slant of eyes
-brushfield spots on iris of eyes
-changes to ear structure
-small nose
-enlarged and protruding tongue
down syndrome
These abnormalities can be present in individuals with what?
-deep palmar crease (simian crease)
-extra space between first and second toe
-hyper flexibility of joints
-decreased muscle tone (hypotonia)
Down syndrome
What are the organ manifestations of down syndrome?
*cardiac defects:
-most common cause of mortality in DS
-atrioventricular septal defects
*gastrointestinal malformations
*vision and hearing loss
*pulmonary infections
What are the growth feature manifestations of Down syndrome?
*short stature
*short fingers
What are the neuropsychiatric manifestations associated with down syndrome?
*behavioral issues:
-issues managing compulsive behaviors and dealing with frustration
*increased risk of Alzheimer’s beginning as early as fifth decade of like (40s):
-affects 40-80% of DS patients
-manifests with early onset of memory loss, then progresses
What occurs in Klinefelter syndrome?
the ovum with XX is fertilized by a sperm with a Y leading to an XXY genotype
Klinefelter syndrome is the most common genetic abnormality that causes what?
primary hypogonadism and infertility
What is hypogonadism?
testicular development is not normal for where it should be leading to small testes
In Klinefelter syndrome, infertility is often due to what?
impaired spermatogenesis
What percentage of those born with Klinefelter syndrome will develop feminine appearing breasts?
50%
Affected individuals with Klinefelter syndrome may have?
*impaired psychosocial skills:
-ADHD, impaired judgement, and impaired insight
*impaired higher language skills
*increased risk of:
-Non-Hodgkin’s Lymphoma
-ulcers of the legs
-diabetes
-lupus
Affected individuals with Klinefelter syndrome will have?
*decreased serum testosterone resulting in:
-small testes
-abnormally low sperm count
-abnormal arm and leg length (tall stature)
*increased risk of breast cancer and pulmonary disease
What occurs in Turner syndrome?
ovum that lacks X fertilized by sperm with X or normal ovum (X) fertilized by sperm lacking X or Y, representing a genotype as XO
Those with turner syndrome will have what type of mental development?
normal mental development
What is the female appearance of individuals with Turner syndrome?
-short stature
-prominent neck skin folds
-wide chest with small breasts
-widely spaced nipples
-ovarian dysgenesis leading to low estrogen and often resulting in infertility with primary amenorrhea
What is amenorrhea?
abnormal menstrual cycle
Those with Turner syndrome have an increased risk of what?
cardiac disease
Why do individuals with Turner syndrome have an increased risk of cardiac disease?
they are more likely to have:
-diabetes
-hyperlipidemia
-hypertension
-cardiac structural abnormalities
-aortic dissection
Besides the increased risk of cardiac disease, what other consequences are associated with Turner syndrome?
-hearing loss
-thyroid disease
-osteoporosis and fracture
-renal structure and abnormalities
-vision/ocular abnormalities
-autoimmune disease
What can taking a family history provide?
clues to genetic diseases within your patient’s family
How many generations should you examine when taking a family history?
all first-degree relatives and parents/offspring–3 generations
What information should you gather when taking a family history?
-age
-sex
-general health
-major illness/disease processes
-cause of death (if applicable)
Describe autosomal inheritance
-inheritance of an allele from one of the 22 pairs of autosomes
-can be either homozygous or heterozygous
-heterozygous may be termed a “carrier” for the disease
In autosomal inheritance, males and females are what?
equally likely to inherit the variant gene
What are the characteristics of autosomal dominant inheritance?
-mutation is a single allele of autosome is enough to cause an altered phenotype or disease
-takes only one affected parent for a child to be affected
-males and females equally affected
-multiple generations are affected causing a vertical pattern (seen in every generation)
What are the characteristics of autosomal recessive inheritance?
-two copies of an autosome must contain the variant/mutation for disease to occur
-both parents must carry the variant for the disease to manifest in the offspring
-affects males and females equally
-may skip generations, causing a horizontal pattern (skipping generations)
Describe x-linked inheritance?
-transmitted via x chromosome
-risk of developing disease related to a mutant X-chromosome gene differs between the sexes
**males are hemizygous (XY) for variant allele
**females can be heterozygous (1 copy) or homozygous (2 copies)
Why are males more likely to develop the mutated phenotype in X-linked diseases?
they only have one X so only one copy of the gene is needed
In X-linked dominant diseases, how many copies of the variant X allele is needed to express the phenotype/condition?
just one
Can a father pass an X-linked dominant disease to his son?
no, he only inherits the Y from his dad
An affected father of an X-linked dominant disease only passes the disease to who?
his daughters (who will be affected)
An affected mother of an X-linked dominant disease passes the disease to who?
both the males and the females
In X-linked dominant diseases, who is affected in every generation?
both males and females in each generation because only one variant of X is needed
In X-linked dominant diseases, who is more severely affected?
males are more severely affected than women and can be lethal in males depending on the allele
X-linked recessive diseases are more common in what gender?
males
Why are X-linked recessive diseases more common in males than females?
the presence of an X mutant in a male has no other X to mask its effect because their genotype of XY, whereas females can have an non-affected X than masks the affect of the variant X since their genotype is XX
An affected mother with an X-linked recessive disease will have what percentage of affected sons?
100% since they get their X from their mother
An affected father with an x-linked recessive disease will have how many affected sons?
none since the sons get an Y from their father
What has their own DNA which encodes tRNA, rRNA, and other proteins?
mitochondria
Why is the transmission of mitochondrial DNA maternal?
sperm does not contribute much to cytoplasm of the zygote
In mitochondrial inheritance patterns, the condition is only transmitted via ____________?
maternal lines
Do affected males of mitochondrial inherited diseases pass the mitochondrial DNA/genes to their offspring?
no
Who does the mother with a mitochondrial inherited condition pass the condition to?
all of her children, both male and female
Most of the conditions seen in practice result from what?
multifactorial inheritance
What is it when genetics plus environment factors or epigenetic changes contribute to a disease, but not all who have the gene develop the disease?
multifactorial inheritance
What are some diseases associated with multifactorial inheritance?
-asthma
-diabetes
-hypertension
-coronary artery disease
-schizophrenia
What is the typical inheritance of genetic imprinting?
the child receives one allele from each parent
What type of inheritance is it when one allele is “silenced” during gamete formation and only when remains functional?
genomic imprinting
What occurs when methyl groups are attached to the DNA sequences during formation of the egg or sperm and methylation represses the expression of that allele while the other remains unchanged?
genomic imprinting
Genomic imprinting affected what gender(s)?
both male and female, but no mechanism is clear
What are some examples of genomic imprinting?
-Angelman Syndrome
-Prader-Willi Syndrome
What condition occurs when the paternal copy of a gene is imprinted (inactivated) and only the maternal allele is active and there is a variant within the maternal allele?
Angelman Syndrome
What condition develops when the maternal copy of a gene is imprinted (inactivated) and only the paternal copy is active and there is a variant within the paternal allele?
Prader-Willi Syndrome
What do both Angelman syndrome and Prader-Willi syndrome result in?
neurodevelopment disorders
