Exceptions to Mendelian Genetics

ABO blood group

ABO blood group

ABO blood groups are types of human blood, and they an example of how a person can have a co-dominant trait. A and B are dominant and O is recessive. The types are A, B, AB and O. (multiple alleles inheritance, AB=co-dominance)

autosome

Any chromosome that is not a sex chromosome

carrier

A person who has one recessive allele for a trait, but does not have the trait.

codominant alleles

Phenotypes of both homozygous parents are produced in the offspring so that both alleles are equally expressed

Color blindness

A sex-linked trait in which an individual cannot perceive certain colors. (sex-linked recessive inheritance)

cystic fibrosis

An autosomal recessive genetic disorder that occurs in people with two copies of a certain recessive allele; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.

fetus

In humans, the term for the developing organism between the embryonic stage and birth.

Hemophilia

An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured. (sex-linked recessive inheritance)

huntington's disease

Rare disease, affects motor and memory, is inherited disease that does not manifest until midlife. (autosomal dominant)

incomplete dominance

A pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits.

karyotype

A picture of all the chromosomes in a cell arranged in pairs

multiple alleles

Three or more forms of a gene that code for a single trait

pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

phenylketonuria (PKU)

An inborn inability to break down the amino acid phenylalanine; it requires elimination of phenylalanine from the diet, otherwise serious mental retardation will result (autosoma recessive)

polygenic inheritance

The inheritance of traits that are controlled by two or more genes, such as height in humans

sex chromosome

Chromosomes that determine the sex of an individual. (X & Y)

sex-linked trait

A trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans

sickle-cell anemia

Red blood cells have a sickle shape and clump together; may result in severe joint and abdominal pain, weakness, kidney disease, or restricted blood flow (autosomal co-dominant)

tay-sach's disease

A human (autosomal recessive) genetic disease caused by a recessive allele that leads to the accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth.

Trisomy 21

Condition in which an individual has three number 21 chromosomes, resulting in Down syndrome (non-disjunction)