18 human genetics

APPLY, INTERPRET pedigrees CC recessive, dominant traits CC non-mendelian traits CC types of genetic testing

What is a dominant trait?

A trait that is always expressed if at least one dominant allele is present.

What genetic cause does a dominant trait require?

Only one allele.

How does a dominant trait affect recessive alleles?

It masks the effect of a recessive allele.

When is a recessive trait expressed?

Only when two recessive alleles are present.

What genetic cause is required for a recessive trait?

Two recessive alleles.

What happens to a recessive trait if a dominant allele is present?

It is masked

What does “autosomal” mean?

Not a sex chromosome

What causes an autosomal recessive disorder?

Two mutated genes that make a faulty or missing protein

How many mutated alleles are needed for an autosomal recessive disorder?

two, one from each parent

Which allele causes disease in autosomal recessive disorders?

the recessive allele

In an autosomal recessive disorder, what does genotype Aa represent?

A carrier (not affected but can pass on the allele).

In an autosomal recessive disorder, what does genotype aa represent?

An affected individual.

In an autosomal recessive disorder, what does genotype AA represent?

An unaffected individual (not a carrier).

What causes an autosomal dominant disorder?

One defective copy of a gene

How many defective alleles are needed for an autosomal dominant disorder?

one

What type of allele causes disease in autosomal dominant disorders?

dominant allele

In an autosomal dominant disorder, what does genotype aa represent?

An unaffected individual.

Changes to chromosome Number: What is the problem?

Gain or Loss of an entire chromosome

Changes to chromosome number: Example

Down syndrome (Trisomy 21)

Changes to chromosome structure: What is the problem?

segment of a chromosome is broken, deleted, or moved (deletion, duplication, Translocation)

X-linked dominant: where is the gene and how many copies cause the trait?

On the x-chromosome; one copy is enough for the trait to show. XAXA (homo dom), XAXa (hetero), XAY (hemi dom)

X-linked Recessive: Where is the gene, and what genotype is needed for the trait?

on the x-chromosome; requires two copies in females (XaXa) or one copy in males (XaY)

X-Linked Recessive: What is a disease example?

Color Blindness or Hemophilia.

What is the primary goal of newborn screening?

Detection of genetic disorders at birth

What types of tests are used in Newborn Screening?

biochemical tests and tests for mutations in genes coding for enzymes in metabolic pathways.

What is Amniocentesis?

Fetal testing involving the removal of 20ml of amniotic fluid, which surrounds the fetus.

What is CVS an acronym for?

Chorionic Villus Sampling

What is the Chorionic Villus?

A component of the placenta and an organ of exchange

What type of disorder is PKU (phenylketonuria)?

Autosomal recessive disorder

In PKU, what is the genotype of the affected individual?

Homozygous recessive

What is the consequence of the buildup of phenylketones?

Damage to the Central Nervous System (CNS).

What foods must be avoided on a low phenylalanine diet?

Meat, fish, dairy, bread, and nuts.