Autosomal Disorders

Question 1

Autosomes

Answer 1

Chromosomes 1-22, not sex chromosomes, source of most genetic information, majority of DNA and genes, show Mendelian inheritance patterns

Question 2

Mendel’s principle of segregation

Answer 2

Two copies of each gene, one per offspring, equal probability for each copy

Question 3

Mendel’s principle of independent assortment

Answer 3

Each gene inherited independently of other genes, genes affecting same function not inherited as a group

Question 4

Multiplication rule of probability

Answer 4

Probability of multiple events occurring together, multiply the risks of each event to get overall risk

Question 5

Addition rule of probability

Answer 5

Probability of either one or another of multiple events occurring, add risks of each to get overall risk, all add up to 1

Question 6

Genotype

Answer 6

Genetic makeup

Question 7

Phenotype

Answer 7

Observable results, some genes have no outward effect on an organism, expression can depend on environmental factors such as diet

Question 8

Autosomal dominant disorders

Answer 8

About 1 in 200 people have autosomal dominant disorder, rare for affected people to mate, usually single affected parent, 50% recurrence risk, requires only one of the affected gene for disease

Question 9

Autosomal dominant inheritance

Answer 9

Affected individuals in each generation, one parent should be affected, both sexes equally affected, father-son transmission is possible, 1/2 of children will be affected

Question 10

Retinoblastoma

Answer 10

Dominant disorder, tumor forms in retina

Question 11

Other dominant disorders

Answer 11

Postaxial polydactylyl, achondroplasia

Question 12

Autosomal recessive disorders

Answer 12

Often the result of mating two carriers, result in 1/4 normal, 1/2 carriers, 1/4 affected, recurrence risk is 25% for each child

Question 13

Autosomal recessive inheritance

Answer 13

May not be found in previous generations, male and females equally affected, 1/4 of offspring will be affected, consanguinity may be a factor (increased risk of same recessive allele in both parents)

Question 14

Albinism

Answer 14

Autosomal recessive disorder, inability to produce melanin from tyrosine

Question 15

Cystic fibrosis

Answer 15

Autosomal recessive disorder, disrupts chloride transport, affects pancreatic secretions due to clogging of ducts, enzymes do not reach intestine, lungs affected by thickened secretions, cannot clear material, excess chloride in sweat

Question 16

Dominant vs. recessive

Answer 16

Homozygotes for dominant disorder are more severely affected, some disorders due to both dominant and recessive genes, categories are for traits not genes

Question 17

New mutation

Answer 17

New mutations occur, suspected when inheritance pattern shows no other affected individuals, parentage of child is confirmed and neither parent has evidence of carrying the mutation

Question 18

Germline mosaicism

Answer 18

Mutation occurs in one of many cells, may be in a few germ cells, cause autosomal dominant or X-linked disorders to appear in unlikely pedigrees

Question 19

Delayed age of onset

Answer 19

Some disorders are not evident until adulthood, children are already produced, too late to make decisions

Question 20

Reduced penetrance

Answer 20

Phenotype mild to non-existent in some individuals due to modifying genes, may affect children much more severely

Question 21

Age-dependent penetrance

Answer 21

Combination delayed age of onset and penetrance, disorder is not obvious until adulthood and may be mild, may affect children more severely

Question 22

Variable expression

Answer 22

Severity of disorder depends on expression, modifying genes can limit expression, appear unaffected, no guarantee that their children will have the same expression

Question 23

Neurofibromatosis

Answer 23

Autosomal dominant with variable expression, some get only a few skin lesions, others get large tumors, “cafe au lait” spots

Question 24

Pleiotropy

Answer 24

Multiple effects from one mutation, single gene affects multiple tissues

Question 25

DNA transcription factors

Answer 25

Used by several specific tissues, example of pleiotropy

Question 26

Extracellular matrix proteins

Answer 26

Expressed at different levels in different tissues, example of pleiotropy

Question 27

Allelic heterogeneity

Answer 27

Multiple mutant forms, different effects, same gene- hemoglobin disorders, sickle cell, beta-thalassemia

Question 28

Locus heterogeneity

Answer 28

Multiple genes affect one pathway, similar disorders but different genetics- 4 of 5 urea cycle disorders

Question 29

Anticipation

Answer 29

Some dominant disorders are more severe in later generations, some age-delayed disorders occur earlier in succeeding generations

Question 30

Repeat expansion

Answer 30

Short sequence of direct repeats in genes, some repeated codons, repeats get longer during meiosis, some threshold number causes disease, greater number can cause earlier and more severe disorder