Mendelian Inheritance and Pedigree Analysis

Question 1

patterns of inheritance

Answer 1

mendelian, multifactorial, and non-mendelian

Question 2

types of mendelian inheritance

Answer 2

autosomal recessive, autosomal dominant, x-linked recessive and dominant

Question 3

types of non-mendelian inheriance

Answer 3

mitochondrial (maternal)

mosaic

imprinted

uniparental disomy

multifactorial

Question 4

traits

Answer 4

autosomal, x-linked, holandric, sex-limited

Question 5

penetrance

Answer 5

the proportion of people with a particular allele (genotype) who manifest the trait (phenotype)

Question 6

expressivity

Answer 6

severity, many traits are not just present or absent, but are present to varying degrees

Question 7

locus

Answer 7

the site on a chromosome where a gene is located

Question 8

alleles

Answer 8

alternative forms of a gene at a particular locus, for most genes, there are two alleles, one on each chromosome

Question 9

Mendel’s First Law

Answer 9

independent segregation - transmission of each allele to offspring with equal frequency

Question 10

Mendel’s Second Law

Answer 10

independent assortment - transmission of an allele at one locus is independent of transmission of alleles at other loci

Question 11

Why is assortment independent?

Answer 11

meiotic recombination - occurs following pairing of homologous chromosomes during prophase I

chiasmata are formed and chromosome material is swapped

Question 12

autosomal recessive inheritance

Answer 12

horizontal transmission

males and females equally affected

risk in siblings is 50% when parent is affected

Question 13

gene dosage effect

Answer 13

the level of gene product in heterozygous carriers is approximately half of the normal amount

Question 14

autosomal recessive disorders

Answer 14

Hemoglobinopathis

Tay-Sachs Disease

Cystic Fibrosis

Gaucher Disease

Phenylketonuria (PKU)

Galactosemia

Oculocutaneous albinism

Infantile polycystic kidney dsease

Hurler syndrom

Question 15

autosomal dominant inheritance

Answer 15

vertical transmission

males and females equally affected

when parent is affected, risk of recurrence in siblings is 50%

Question 16

autosomal dominant disorders

Answer 16

Marfan syndrome

Neurofibromatosis

Adult-type polycystic kidney disease

Aoert syndrome

Osteogenesis imperfecta

Achondroplasia

Huntington disease

Question 17

Codominant traits

Answer 17

traits determined by both alleles are expressed

at the biochemical and molecular level, most alleles are codominant

Question 18

x-linked recessive traits

Answer 18

usually expressed only in males

both parents are noirmal

if mother is a carrier, 50% of the daughters will be carriers, and 50% of the sons will be affected

if the father is the carrier, all of the daughters will be carriers, and none of the sons will have the trait

Question 19

x-linked disorders

Answer 19

Red-green color blindness

Glucose-6-phosphate dehydrogenase deficiency

Hemophilia

Fragile-X syndrome

Duchenne muscular dystrophy

Question 20

x-linked dominant traits

Answer 20

expressed in males and females

transmitted from mothers to sons and daughters, and from fathers only to daughters

no father to son dtransmission

if mother has the trait, 50% of daughters will have it, and 50% of sons will be affected

if father has the trait, all of the the daughters will have it, and none of the sons will be affected

Question 21

hemizygosity

Answer 21

males have only one X chromosome, and therefore only one allele, so a defect in one allele may produce disease in males

Question 22

Lyonization

Answer 22

x-chromosome interaction early in female development, randomly determined and maintained with subsequent mitotic divisions - leads to mosaicism

Question 23

genetic fitness

Answer 23

the capacity for an organism to procreate, depends on survival to reproductive age

Question 24

new mutations

Answer 24

one of the common causes of recurrence of some more severe mutations

Type I collagen, neurofibromin, fibroblast growth factor receptor 3

Question 25

Haldane rule

Answer 25

in the case of lethal x-linked disorders, the gene frequency is stable because of new mutations, which account for ~1/3 of all cases

Question 26

linkage

Answer 26

when genes are very close together, they may not segregate independently but instead be transmitted together

not absolute, always a probability of them being transmitted together

Question 27

four practical applications of linkage analysis

Answer 27

prediction of phenotype, determination of location of genes, association of specific genes with phenotypes, study of complex traits

Question 28

sickle cell mutation

Answer 28

single A to T transversion mutation causes a glutamine to be turned into a valine

Question 29

neurofibromatosis

Answer 29

common genetic disorder resulting from dominant mutations in the NF1 gene

earliest most common sign is the development of cafe-au-lait spots

patients with neurofibromatosis develop multiple benign tumors, and may develop malignancies and other complications