Definitions + Misc.

Question 1

Congenital

Answer 1

A condition or anomaly present at birth.

Question 2

Hereditary

Answer 2

Refers to conditions that are genetically transmitted from parents to offspring.

Question 3

Familial

Answer 3

Refers to conditions that “cluster” in families and can include genetic as well as nongenetic (e.g. ADHD, HTN) conditions.

Question 4

Genotype

Answer 4

The genetic makeup of an individual, or different forms of a gene at a given locus on a chromosome.

Question 5

Phenotype

Answer 5

The observed expression (physical, biochemical, or physiological) of a genotype.

Question 6

Penetrance

Answer 6

The ability of a known disease-causing genotype to exhibit the disease phenotype.

Question 7

Describe the penetrance for a condition in which 10% of the population with the disease-causing genotype do not go on to develop the disease.

Answer 7

The penetrance in this situation would be 90%.

Question 8

Variable expressivity

Answer 8

When individuals who have the same genetic condition/genotype have varying degrees of the associated phenotype.

Question 9

Genomic Imprinting

Answer 9

Imprinting turns of selected genes, so the expression of the gene depends on whether the gene was inherited from the mother or the father.

Question 10

Pleiotropic

Answer 10

Refers to genes that produce many effects. An example is Marfan syndrome, which can affect the eyes, cardiovascular system, and skeletal system.

Question 11

Mosaicism

Answer 11

The presence of ≥2 genetically different sets of cells in the same person caused by an error in mitosis.

Question 12

Heterozygous

Answer 12

Refers to the presence of two different alleles at a gene locus on a pair of homologous chromosomes.

Question 13

Homozygous

Answer 13

Refers to the presence of two identical alleles at a gene locus on a pair of homologous chromosomes.

Question 14

Autosome

Answer 14

Refers to all chromosomes except the X and Y chromosomes.

Question 15

Nondisjunction

Answer 15

Occurs when homologous chromosomes or chromatids fail to separate, resulting in an abnormal number of chromosomes in the daughter cells.

Question 16

Aneuploidy

Answer 16

Refers to the presence of an abnormal number of chromosomes in a cell.

Question 17

Complex

Answer 17

Anomalies of several different structures that are near each other during embryonic development (ex: limb-body wall complex)

Question 18

Association

Answer 18

Anomalies seen together that do not have a known single genetic or developmental etiology (ex: VACTERL)

Question 19

Syndrome

Answer 19

A recognizable pattern of structural defects, due to a known single genetic etiology, with a predictable natural history that remains relatively consistent across unrelated patients (ex: Cornelia de Lange, Williams)

Question 20

Balanced Translocation

Answer 20

An even exchange of genetic material between chromosomes, resulting in no extra or missing genes.

Question 21

Unbalanced Translocation

Answer 21

An uneven exchange of genetic material between chromosomes, resulting in extra or missing genes.

Question 22

Sequence

Answer 22

A pattern of multiple anomalies caused by a single identifiable even in development (ex: Pierre Robin sequence)

Question 23

What is multifactorial inheritance?

Answer 23

Genetic disorders which are due to multiple genetic and environmental factors rather than a “single gene” mutation.

Question 24

What (7) factors suggest multifactorial inheritance has occurred?

Answer 24

There is no discernable Mendelian inheritance pattern; recurrence risk increases as the number of affected individuals in the family increases; recurrence risk is higher if the affected individual is a member of the less commonly affected sex; recurrence risk is higher if the individual has a more severe form/case; recurrence risk drops dramatically as the degree of familial relationship decreases from the affected individual; recurrence risk correlates with the prevalence in the general population; and environmental factors play a role.

Question 25

Are dizygotic twins more likely, less likely, or equally likely to have genetic traits similar to those of a nontwin sibling?

Answer 25

From a straightforward genetic perspective, dizygotic twins are no more similar than nontwin siblings.

Question 26

Name 4 diseases or abnormalities that are more likely to be concordant in monozygotic than dizygotic twins.

Answer 26

Autism (60% vs 0%), Cleft lip/palate (38% vs 8%), clubfoot (32% vs 3%), and spina bifida (72% vs 33%).