Genetics Flashcards
What is a Genotype?
the genetic makeup of a person
What is a Phenotype?
the physical manifestation of an inherited trait or disease
When do you consider a referral to genetics? (6)
- developmental delay
- dysmorphic features
- congenital malformations
- a positive family history of a genetic disorder
- recurrent miscarriages/still births
- consanguinity
What are some disorders that become more common due to founder effect/consanguinity? (6)
- Ashkenazi Jewish: Tay-Sachs, BRCAI
- Mediterranean: beta-thalassemia
- Southeast Asian: alpha-thalassemia
- Amish/Mennonite and Arab: various rare disorders
- African: sickle cell anemia
- Caucasian: cystic fibrosis
What are G/Giemsas?
Banded Chromosomes
What are the largest chromosome pairs?
Number 1
What are the smallest chromosome pairs?
Number 2
Which chromosomes determine sex?
Chromosome 23
What are the different Chromosomal Disorders?
- Numerical Chromosome Anomaly
- Structural Anomaly
What is Numerical Chromosome Anomaly?
Error which occurs in Meiosis (1 or 2), resulting in aneuploidy (monopsony or trisomy) or triploidy
What is Structural Anomaly?
Error of recombination
What is the most common cause of Trisomy 21?
Nondisjunction
What is Trisomy 21?
When a person has an extra chromosome 21
Results in Down syndrome
What are the characteristics of Down Syndrome?
- distinct facial features
- developmental delay
- heart defects
In which population is Trisomy 21 most common? (3)
- Mothers of advanced maternal age
- due to cell division completing in mothers after ovulation and further after fertilization
- with time, those chromosomes become very sticky as the age of the egg advances
What are the different ways Trisomy 21 can occur? (3)
- nondisjunction
- Translocation
- Mosaic
What are Structural Chromosome Anomalies? (3)
- Caused by error of recombination
- May be balanced - translocation (reciprocal or robertsonian) or inversion
- may be unbalanced - deletion, duplication, translocation, inversion
What are the different Chromosome Disorders? (4)
- Trisomy 13
- Trisomy 18
- Turner Syndrome (45x)
- Klinefelter Syndrome 47, XXY
What is Trisomy 13? (5)
- also known as Palau Syndrome
- Midline defects are common
- extra fingers
- 80-90% die in first year
- Severe developmental delay
What is Trisomy 18? (5)
- also known as Edward Syndrome
- Most are female (5:1)
- Frequent cardiac defects
- 80-90% die in first year of life
- Marked developmental delay
What is Turner Syndrome? (7)
- disorder in which there is only one X chromosome
- puffy hands and feet at birth
- webbed neck
- coarctation of aorta
- short stature
- primary amenorrhea and infertility (streak ovaries)
- Normal intelligence
What is Klinefelter Syndrome? (7)
- disorder in which there is an extra X chromosome XXY
- Tall stature
- Excess breast development
- small testes
- infertility
- normal appearance
- may have learning disabilities
Who is the father of Genetics?
George Mendel
What did George Mendel do?
He worked with seven characteristics of pea plants, and crossed them to see what he could get, looking at the genetics
What is Autosomal Dominant? (5)
- Diseases/disorders that run in families
- usually present in every generation
- not tied to a X chromosome
- Males and females are affected equally
- about 50% transmission
What is an example of an Autosomal Dominant Disease?
Polycystic Kidney disease
What is Autosomal Recessive? (4)
- diseases/disorders in which the person inherits two changed genes
- majority of people are carriers, but it does not affect their health
- Males and females are effected equally
- Consanguinity increase the number of individuals affected
What is an example of Autosomal Recessive Disease?
Cystic Fibrosis
What is Cystic Fibrosis? (3)
- When we have mutations or changes in the gene CFTR
- It codes for the CFTR protein which is responsible for chloride channels
- it starts to affect the mucus and motility of the cilia
What are the characteristics of an X-linked Inheritance? (4)
- Males affected almost exclusively
- the gene alteration can be transmitted from female carriers to sons, but the females are often asymptomatic
- affected males cannot transmit the condition to their sons
- carrier females may be mildly affected or fully affected due to skewed X inactivation
Why are males affected by X-linked disorders?
- only 1 X chromosome
- must express all x-linked genes
- hemizygous
What is Duchenne Muscular Dystrophy? (5)
- X-linked disorder that impacts the gene called DMG
- this gene codes for dystrophin, which is important in the muscles
- affected males die in their early 20s due to cardiomyopathy
- mutation may be inherited from mother or new mutation
- high spontaneous mutation rate
What occurs in boys who have Duchenne Muscular Dystrophy?
- They will present early on with progressive breakdown of muscles
- One of the signs is hypertrophy, fatty tissue as opposed to muscle
- progressive muscle weakness
What are the characteristics of Mitochondrial DNA Disorders? (4)
- all mitochondria are inherited from the mother through the egg
- mitochondria have their own circular DNA
- expectation is to have maternal inheritance, and all her offspring will have it/carry it
- severity depends on the abnormality of the mitochondria genetic material
What are the Symptoms of Mitochondrial Multi-systemic Disorders? (6)
- Muscle = fatigue and low tone
- Brain = cognitive dysfunction
- Digestive = feeding difficulties, constipation
- Cardiac = cardiomyopathy
- Eye = limited eye movement
- Diabetes
