Genes & Genetic Mutations

Genetics

Study of biologic inheritance

Chromatin

Substance giving the nucleus a granular appearance, forms chromosomes

Down Syndrome is trisomy?

Trisomy 21

Down syndrome is what?

Autosomal aneuploidy

Down syndrome characteristics

- Pregnancy in women older than 35 years
- Flat facial profile
- Growth failure
- Leukemia risks
- Heart problems
- Mental retardation ranges

Down syndrome affects what sexes?

Both sexes affected equally

Turner syndrome is what?

Sex aneuploidy
- X, 45

Turner syndrome characteristics?

- Short stature
- Webbed neck
- No menstrual cycles
- Broad chest

Turner syndrome affects what sex?

Females only

Klinefelter syndrome is what?

Sex aneuploidy
- XXY, 47

Klinefelter syndrome characteristics?

- Gynecomastia
- Tall frame
- Wide hips
- Long arms and legs
- No facial hair

Klinefelter affects what sex?

Males only

Cri du chat syndrome is what?

Autosomal deletion (of chromosome 5)

Cri du chat syndrome characteristics?

- Crying sounds like a "cat"
- Heart defects
- Microcephaly
- Severe mental retardation

Cri du chat syndrome affects what sex?

Both sexes

Autosomal dominant diseases?

- Huntington disease
- Neurofibromatosis/von Recklinghausen disease
- Marfan's syndrome

Autosomal aneuploidy diseases?

Down syndrome (trisomy 21)

Sex chromosome aneuploidy diseases?

*X is always dominant here
- Turner syndrome
- Klinefelter syndrome

Autosomal recessive diseases?

- Cystic fibrosis
- Sickle cell disease
- PKU
- Tay-Sachs disease

Sex-linked inheritance/X-linked recessive diseases?

Hemophilia

Locus

Position of a gene

Gene

Unit of heredity

Alleles

Variation of a gene

Homozygous dominant

AA

Heterozygous dominant

Aa

Homozygous recessive

aa

How many pairs of chromosomes?

23

How many total chromosomes?

46

How many autosomes?

22 autosomes

How many pairs of sex chromosomes?

1 pair (either XX or XY)

Aneuploidy

The presence of, or absence of one or more chromosomes; does not contain a multiple of 23 chromosomes

Monosomy

Presence of only one copy of any chromosome
*LETHAL

Trisomy

A cell containing 3 copies of one chromosome

Nondisjunction

Cause of an aneuploidy, failure to separate properly during mitosis/meiosis

Penetrance

Percentage of individuals with a specific genotype with expected phenotype; the probability of a trait being expressed

Incomplete penetrance

Individual who has a gene for a disease but does not express the disease

Expressivity

Extent of variation in a phenotype associated with a genotype; variation in phenotypic expression

Autosomal dominant diseases do not...

Skip generations

Huntington disease traits

*Autosomal dominant
- Chromosome 4
- Degenerative disorder of the cerebral cortex
- 5 year survival
- CHOREA

Neurofibromatosis traits?

*Autosomal dominant
- Chromosome 17
- Cafe au lait

Consanguinity

Mating of 2 related individuals

Cystic fibrosis traits

*Autosomal recessive
- Most common in Caucasians
- Defective CFTR gene
- Lungs and digestive tract affected

Sickle cell disease traits?

*Autosomal recessive
- Most common in African Americans
- Deoxygenation in RBCs lead to sickle shape
- Has decreased recently

Hemophilia traits?

*X-linked
- Serious bleeding disorder
- Inherited from MOTHER --> SON

X-Linked disorders differences?

*Are recessive disorders

*AFFECTED MOTHER --> SON
*AFFECTED FATHER --> ALL DAUGHTERS AFFECTED

Autosomal recessive diseases do...

Skip generations and have carriers

Autosomal recessive disease parents?

Both parents are usually heterozygous carriers
*Recurrence risk is ~25% for offspring

Recurrence risk

The probability that an individual will develop a genetic disease

*Ex: Autosomal dominant, 1 parent affected, 1 parent normal = 1/2 for each child