Mendelian Genetics

Question 1

Somatic Cells

Answer 1

Cells that are not gametes. Contain 2 copies of each chromosome (1-22) and either XX or XY

Question 2

Autosome

Answer 2

Any chromosome not considered a sex chromosome (1-22)

Question 3

Allosome (Gonosome)

Answer 3

Sex chromosomes (X and Y)

Question 4

Gametes

Answer 4

Ova and sperm cells. Contain 1 copy of each chromosome (1-22) and either X or Y.

Question 5

Haploid

Answer 5

Having one copy of each chromosome.

Question 6

Diploid

Answer 6

Having 2 copies of each chromosome.

Question 7

Homologous Chromosomes

Answer 7

The two chromosomes in a diploid pair. Contain the same genes but one is paternal origin and one is of maternal origin.

Question 8

Gene

Answer 8

A sequence of DNA that encodes a specific protein or RNA

Question 9

Allele

Answer 9

One of several alternative forms of a gene sequence at a locus.

Question 10

Polymorphism

Answer 10

When a locus has multiples alleles present in a population. A genetic variant with at least two alleles and occurs in at least 1% of the population.

Question 11

Locus

Answer 11

A specific chromosomal location.

Question 12

Wild-Type

Answer 12

Allele present in the majority of individuals. Not deleterious.

Question 13

Mutant

Answer 13

Allele that differs from the wild-type due to mutation.

Question 14

Genotype

Answer 14

Set of alleles an individual possesses.

Question 15

Phenotype

Answer 15

Expression of the alleles. Protein present in clinical manifestation.

Question 16

Homozygous

Answer 16

Two alleles at a particular locus are identical.

Question 17

Heterozygous

Answer 17

Two alleles at a particular locus are different.

Question 18

Hemizygous

Answer 18

X-linked genes in males.

Question 19

Pleiotropism

Answer 19

A single mutant gene may result in many phenotypic variants.

Question 20

Oculodentodigital Dysplasia

Answer 20

Example of Pleiotropism. A connexion mutation. Clinical Features: Thin nose, microcephaly, microphthalmia, microcornea, microdontia, partial adontia, hand and foot abnormalities.

Question 21

Mendelian Inheritance

Answer 21

Single Gene (20%). Two categories of single-gene inheritance; autosomal and gonosomal.

Question 22

Complex Inheritance/Multigenic

Answer 22

Unsure of specific mode. Complex. 50%

Question 23

Environmental teratogen

Answer 23

Environmental factor. 5%

Question 24

Chromosomal Imbalance

Answer 24

25%

Question 25

Dominant

Answer 25

Allele that is always expressed, even if another allele is present.

Question 26

Incompletely dominant

Answer 26

Expression of two different alleles results in an intermediate phenotype. For example: A red rose is crossed with a white rose. Offspring are pink roses.

Question 27

Codominant

Answer 27

Each allele results in an observable phenotype. For example: Blood type.

Question 28

Recessive

Answer 28

Requires the presence of two identical alleles to express an observable phenotype.

Question 29

Loss-of-function

Answer 29

Reduced production of a gene product or inactive protein. Most common.

Question 30

Gain-of-function

Answer 30

Gene product gains new function. Most often toxic properties. Sometimes increased activity (for example receptor activation). Note: Not necessarily a good gain.

Question 31

Recurrence Risk

Answer 31

The probability that the offspring of a couple will express a genetic disease.

Question 32

Autosomal Dominant Disorders

Answer 32

1. Disorder is manifested in the heterozygous state 2. Both males and females affected 3. Most often affects enzymes, receptors, feedback inhibitors, and structural protein

Question 33

Dominant Negative Allele

Answer 33

Mutant allele negatively affects a normal allele. Multimeric proteins

Question 34

Autosomal Dominant Pedigree

Answer 34

1. Disease typically observed over multiple generations. 2. Skipped generations unlikely to be seen. 3. Males and Females equally affected.

Question 35

Haploinsufficiency

Answer 35

Normal physiology requires more than half of the fully functioning gene product. Can be sporadic, resulting from a new mutation.

Question 36

Penetrance

Answer 36

The frequency (%) in which the allele expresses itself phenotypically.

Question 37

Incomplete Penetrance

Answer 37

An individual inherits the allele but is phenotypically normal.

Question 38

Variably Expressed

Answer 38

All individuals express the phenotype but to different degrees.

Question 39

Autosomal Recessive Disorder

Answer 39

1. Parents of affected usually unaffected. 2. Usually completely penetrant. 3. Onset is usually early in life. 4. Usually not a new mutuation.

Question 40

Margin of Safety

Answer 40

Heterozygous individuals with half the normal content function normally.

Question 41

Autosomal Recessive Pedigree

Answer 41

1. Typically only seen in one generation | 2. Males and Females equally affected.

Question 42

Consanguinity

Answer 42

The mating of related individuals Individuals who share common ancestors are more likely to carry the same recessive allele.

Question 43

X-Linked disorders

Answer 43

Those affecting gonosomes. Most Y-linked disorders cause infertility so this is generally not considered a pattern of inheritance.

Question 44

X-linked recessive disorders

Answer 44

Almost all X-linked disorders are recessive. All affected males will be hemizygosity. Heterozygous females usually don't express the full phenotypic change.

Question 45

X-Linked dominant disorders

Answer 45

Few Exist.

Question 46

X-linked recessive pedigree

Answer 46

Males are more commonly affected. Skipped generations are common. Male to male transmission not seen.

Question 47

X-linked dominant pedigree

Answer 47

Male to male transmission not seen. Heterozygous females are affected so expressed twice as often in females. Skipped generations unusual. No sons but all daughters of an affected male will express the disease.

Question 48

X-Inactivation/Dosage Compensation (General Overview)

Answer 48

1. Inactivates copy of the X chromosome in all somatic cells of females. 2. Begins during blastocyte formation 3. Condensed into heterochromatin 4. Gene regions methylated. 5. Barr Body

Question 49

Barr Body

Answer 49

Highly condensed chromosome visible in the nuclei of interphase cells.

Question 50

X-Inactivation/Dosage Compensation (Rules)

Answer 50

1. Random: 50% chance in each cell that either the maternal or paternal X chromosome is inactivated. Genetic Mosaicism. 2. Fixed: Once inactivated, every descendent of the cell will have the same X chromosome inactivated. 3. Incomplete: Some regions not inactivated. Manifesting heterozygotes.

Question 51

Genetic Mosaicism

Answer 51

Condition in which cells with different genotypes or chromosome constitutions are present in the same individual.

Question 52

Manifesting heterozygotes

Answer 52

Some females will express an X-linked recessive mutation due to X-inactivation.

Question 53

Myotonic Dystrophy

Answer 53

Autosomal dominant condition with variable expression in clinical severity and age at onset. Manifests as bilateral cataracts, moderate facial weakness and ptosis, myotonia.

Question 54

SHH Mutation (Sonic Hedgehog)

Answer 54

Variable expressivity.Caused by a missense mutation. For example: Mother has a single central upper incisor. Daughter is severely affected with microcephaly, abnormal brain development, hyp-telorism, and cleft palate.

Question 55

Expressivity

Answer 55

The severity of expression of the phenotype among individuals with the genotype.

Question 56

Allelic Heterogeneity

Answer 56

Different mutations can be responsible for more or less severe expression. Usually not within a family.

Question 57

Pleiotropy

Answer 57

A single disease causing mutation affects multiple organ systems.

Question 58

Locus Heterogeneity

Answer 58

A single disorder is caused by mutations at different chromosomal loci.

Question 59

Point Mutations

Answer 59

Replace one nucleotide with another.

Question 60

Missense mutation

Answer 60

Alters the meaning of the sequence such that it encodes a different amino acid. May or may not affect the overall protein structure.

Question 61

Nonsense Mutation

Answer 61

Alters the meaning of the sequence to a STOP codon. Protein is truncated. (Stop this nonsense!)

Question 62

Frameshift Mutations

Answer 62

Insertion or Deletion into a sequence. If not a multiple of three, entire message is changed in the sequence following it. If a multiple of three, subsequent protein will lose or gain an AA.

Question 63

Trinucleotide Repeat Mutations

Answer 63

Amplification of a sequence usually containing Cs and Gs. Dynamic or continually changing during cell division.