Genetics - Midterm 1

Question 1

What is Duchenne muscular dystrophy? Characteristics? What does it affect?

Answer 1

X-linked recessive disorder

-Progressive muscle degeneration
-Aff ects heart and respiratory muscles; death by respiratory or cardiac failure usually occurs before age 20
-Portions of the DMD gene are deleted, causing absence of the protein dystrophin.

Question 2

What is the Prodromal period?

Answer 2

person experiences vague symptoms (fatigue, loss of appetite) before speci c symptoms/signs set in

Question 3

Newborns with which trisomy can survive birth?

Answer 3

Newborns with trisomy 13, 18, 21, or X can survive

Question 4

Ex of an autosomal recessive disorder? What are its characteristics?

Answer 4

cystic fibrosis (Occurs in 1/2500 births in white children)

-Gene responsible codes a chloride ion channel in some epithelial cells; defective transport of chloride leads to salt imbalance that results in thick mucus- lungs become clogged and pancreas may become obstructed.

-Death from lung disease/heart failure occurs in 1⁄2 of people before age 40.

-Both parents contribute a copy of the gene, 25% of o spring will be normal, 50% will be carriers (have gene but not disease), 25% will have disease

Question 5

What are Polyploid cells?

Answer 5

when a euploid cell has more than the diploid number of chromosomes (liver, bronchial, and epithelial tissues).

Question 6

What is Pathogenesis?

Answer 6

the pattern of tissue changes associated with the development of disease.

Question 7

Polygenic traits Vs Multifactorial traits?

Answer 7

Polygenic traits: traits that result from several genes acting together.

Multifactorial inheritance: When environmental factors also in fuence the expression of a trait

Question 8

What is down syndrome? What are its characteristics? What causes it?

Answer 8

-It is a trisomy of chromosome 21
-Low nasal bridge, epicanthal folds, protruding tongue, low-set ears, Hypotonia and short stature
-Cause: nondisjunction during formation of one parent’s gametes or during early embryonic development (mostly mother’s egg cell)
-By age 40 alzhimer symptoms

Question 9

What are Euploid cells?

Answer 9

cells with a multiple of the normal number of chromosomes. Gametes and most somatic cells

Question 10

What is Retinoblastoma? Characteristics? Caused by?

Answer 10

-Autosomal dominant disease

-Most common malignant eye tumors in children

-Exhibits incomplete penetrance (90%)

-10% are obligate carriers (those who have an affected parent and affected children and therefore must themselves carry the mutation) who do not have the disease

-Caused by a mutation in the tumour suppressor gene.

Question 11

What are single-gene disorders caused by? Recurrence rate?

Answer 11

-Caused by single gene that is defective or mutated

● Recurrence rate for single-gene diseases remains the same regardless of the number of siblings a ffected

Question 12

Aneuploidy of chromosome 21 results in?

Answer 12

Down syndrome

Question 13

What is Klinefelter syndrome? What are its characteristics? What is it caused by?

Answer 13

-2 X chromosomes and one Y chromosome (Karyotype:47,XXY)

-Moderate degree of mental impairment
-Gynecomastia (development of breasts) in 50% of cases.
-Male appearance but usually sterile
-High pitched voice
-Small testicles. Sparse body hair. Long limbs
-Caused by nondisjunction in X chromosome of mother

Question 14

Risk factors Vs Precipitating factors?

Answer 14

Precipitating factor: is a condition or event that does cause a pathological event or disorder. E.g. allergen precipitates asthma

Risk factors (predisposing factors), increase the probability that disease will occur, but these factors are not the cause of disease. (Hereditary, gender, race, environment, and lifestyle)

Question 15

More (blank) are affected by X-linked recessive diseases then females?

Answer 15

Males

Question 16

Remission Vs Exacerbation periods?

Answer 16

Remissions are periods when symptoms disappear or diminish signi cantly.

• Exacerbations are periods when the symptoms become worse or more

Question 17

What is Neuro fibromatosis type 1? Characteristics? What causes it it? What can it result in?

Answer 17

(tumors all over the body) - Autosomal dominant

-Expression of the disease varies from few harmless light brown spots on skin to neuro bromas, scoliosis, seizures, gliomas, neuromas, malignant peripheral nerve sheath tumours, hypertension, and learning disorders (variable expressibility)

Caused by tumour suppressor gene mutation.

■ One heterozygous parent has the gene and the other parent is unaffected: 50% of o spring will be normal, 50% will be heterozygous and have the disease. There will be no carriers

■ Can also occur from mutation in one of the parent’s genes.E

Question 18

What is monosomy? What is it lethal in?

Answer 18

(common form of aneuploidy)
-only one copy of a given chromosome in diploid cell. In autosomes, it is lethal.

-Loss of chromosome material is more serious than duplication of chromosome material.

Question 19

What are Insidious symptoms?

Answer 19

feeling that there is a change in the body, its Vague!

Question 20

What are Triploidy cells? What do they result in?

Answer 20

zygote that has 3 copies of each chromosome. Nearly all are spontaneously aborted or stillbirth

Question 21

What is Huntingtons’ disease? Characteristics? it is caused by?

Answer 21

-Autosomal dominant disease
-Incurable neurological disease
-causing death early on in life

*Main features are progressive dementia and uncontrollable limb movements and Delayed age of onset (40 years)

-Caused by trinucleotide repeat mutation.

Question 22

Examples of autosomal dominant diseases?

Answer 22

-Huntingtons disease
-Retinoblastoma
-Neuro bromatosis type 1

Question 23

Affected father and normal mother combination for X-linked recessive disorders?

Answer 23

Aff ected father and normal mother: all daughters are carriers, and all sons are normal

Question 24

What is gene mosaicism?

Answer 24

all or part of the germline of a parent has undergone
mutation when they were an embryo; the parent can then transmit the disease to multiple o spring

Question 25

What is turners syndrome? What is it caused by? Characteristics? Found only in?

Answer 25

The presence of single X chromosome with no other X or Y (Karyotype: 45,X.)
-Found only in females

-Short stature, wide-placed nipples, webbing of neck, reduced elbow carrying angle

■ Coarctation(narrowing of aorta), sterility, gonadal streaks instead of ovaries

■ Caused by a meiotic error in the father

Question 26

Autosomal recessive disease/traits characteristics?

Answer 26

Disease is rare
○ Must have two recessive genes for disease to occur or else normal gene will compensate and/or take over

○ Recurrence rate: 25%

○ Males and females are a ffected equally

○ Consanguinity is sometimes present

○ On average, 1⁄4 o spring of carrier parents will be a fected (in most cases, both parents are heterozygous carriers)

○ Passed on from generation to generation by hiding in carriers

Question 27

What kind of cell contains three copies of one chromosome? What does it result in? What is it the result of?

Answer 27

-Aneuploid cell
-Result of nondisjunction

Results in:
-Monosomy
-Partial Trisomy

Question 28

Why do females become carriers of X-linked diseases?

Answer 28

-The XX has a second chromosome to compensate, making women carriers
-The XY cannot compensate for abnormal X, meaning men will inherit the disease

Females become carriers, males inherit disease from mother

Question 29

Signs Vs Symptoms?

Answer 29

Signs: objective. Can be local (swelling) or systemic (fever)

Symptoms: subjective. Pain, nausea, shortness of breath

Question 30

What is trisomy X? What are its characteristics?

Answer 30

Females have 3 X chromosomes
-No overt physical abnormalities
-Sterility, menstrual irregularity, and intellectual disability may sometimes occur
More Xs added =more mental impairment

Question 31

What does the term “threshold of liability” refer to?

Answer 31

For some diseases, a threshold of liability must be passed before it is expressed. Below the threshold, the individual appears normal.

Question 32

Aneuploidy of sex chromosomes is less serious than that of?

Answer 32

autosomes

Question 33

Autosomal dominant disease/traits characteristics?

Answer 33

-Rare diseases
○ Does not skip generations
○ Recurrence rate: 50%
○ Males and females are equally likely to transmit trait to o spring
○ Only need one dominant gene for disease to occur, other gene will not be able to
compensate

Question 34

What is tetraploidy?

Answer 34

Condition in which euploid cells have 92 chromosomes (fetuses generally don’t survive)

Question 35

Ex of an X-linked disorder?

Answer 35

Hemophilia

Question 36

What is Pyloric stenosis? Characteristics? What is its threshold liability?

Answer 36

it’s the narrowing/obstruction of the pylorus

-Constipation, vomiting, weight loss, and electrolyte imbalance

-Threshold of liability is lower in males than females, thus fewer defective alleles are required to generate the disorder.

Cleft lip, cleft palate, neural tube defects, clubfoot, and some forms of congenital heart disease

Question 37

Incidence Vs Prevalence?

Answer 37

Incidence = number of new cases in a specfi c time

Prevalence = existing disease at any given time

Question 38

What is a Aneuploid cell? What is the result of? What can it result in?

Answer 38

cell that does not contain a multiple of 23 chromosomes. Result of nondisjunction (homologous chromosomes/sister chromatids do not separate normally during mitosis or meiosis). Result is either trisomy or monosomy of that chromosome.

Question 39

Disease (what does it cause) Vs Illness

Answer 39

Disease = acute or chronic illness you’re born with causing physiological dysfunction

Illness = person’s experience of a disease, or state of discomfort or pain without identi able reason

Question 40

What is the Most common combination for X-linked recessive diseases?

Answer 40

Carrier mother and normal father, half sons are a ffected and half of the daughters are carrier