Genetics

Describe the basic pattern of inheritance.

A person receives 1 set (23) of chromosomes from each parent. They receive two variants (alleles) of each gene. One allele is dominant (more powerful) and the other is recessive (weaker). Offspring will express the dominant allele in heterozygous genes and will express the recessive allele only if they are homozygous for it.

Differentiate homozygous and heterozygous.

• Homozygous means an individual received the same allele from each parent for a specific gene.

• Heterozygous means an individual received different alleles from each parent.

Describe Autosomal Dominant inheritance and who is affected.

If one parent carries a single dominant allele, the offspring has a 50% chance of inheriting the disorder. It is transmitted to both XX (female) and XY (male) offspring. (Example: Marfan Syndrome).

Describe Autosomal Recessive inheritance and who is affected.

Single gene mutations are passed on from 2 affected parents (carriers). The disease occurs only in homozygous pairs (must have 2 recessive genes). It affects both XX and XY individuals. Heterozygous individuals are carriers with no symptoms. (Example: Tay-Sachs)

Describe Sex-Linked inheritance and who is affected

Mutations are located on the X chromosome. Females (XX) are more likely to be carriers, while males (XY) are more likely to be affected because they only have one X chromosome. (Example: Fragile X Syndrome).

Describe Multifactorial and Chromosomal Disorders and who is affected.

• Multifactorial: Results from an interaction between environmental and genetic factors. Less predictable with no traceable pattern. (Example: Cleft Lip/Palate).

• Chromosomal Disorders: Caused by a variation in chromosomal duplication (extra copy) due to environmental influences like parental age, drugs, or infections. Affects the embryo early in development (days 15-60). (Example: Trisomy 21).

Discuss the common clinical manifestations of Marfan Syndrome.

• Increased height

• long extremities & fingers

• thin/narrow face

• aortic defects

• myopia (nearsightedness)

• and spine & chest deformities

Discuss the common clinical manifestations of Tay-Sachs Disease

• Progressive mental and motor deterioration

• Life expectancy is 3-5 years. (Caused by lipid accumulation in nerve cells leading to demyelination).

Discuss the common clinical manifestations of Fragile X Syndrome.

• Intellectual disabilities

• behavioral/learning disabilities

• hyperactivity

• inattentiveness

• seizures

• long, narrow face with large ears, jaw, and forehead.

Discuss the common clinical manifestations of Cleft Lip/Palate

A spectrum of severity (1/800 births). Treatment includes feeding/breathing support, surgery, and speech therapy.

Discuss the common clinical manifestations of Trisomy 21 (Down Syndrome).

• Hypotonia

• distinctive facial features

• congenital heart defects

• single hand crease

• developmental delays

• behavioral/learning challenges