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chromosomal theory of inheritance

Mendelian genes have specific positions on chromosomes, and it is the chromosomes that undergo segregation and independent assortment.


An individual with the normal (most common) phenotype.


an individual whose DNA or chromosomes differ from some previous or normal state

linked genes

genes located on the same chromosome that tend to be inherited together

genetic recombination

the production of offspring with combinations of traits differing from those found in either parent

parental types

Offspring with a phenotype that matches one of the parental phenotypes

recombinant types

when offspring display phenotypes that are different than parents

crossing over

process in which homologous chromosomes exchange portions of their chromatids during prophase I of meiosis

linkage map

A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes

map unit

A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.

sex-linked genes

A gene located on a sex chromosome

Duchenne muscular dystophy

Progressive weakening of the muscles and loss of coordination - caused by a lack of muscle protein called dystophin. Inheritance pattern: X-linked recessive


sex-linked recessive disorder defined by the absence of one or more proteins required for blood clotting

color blindness

A sex-linked recessive trait in which an individual cannot perceive certain colors

Barr body

Inactivated X in females


abnormal number of chromosomes


extra chromosome (caused by nondisjunction)


missing chromosome (caused by nondisjunction)


condition in which an organism has extra sets of chromosomes


change to a chromosome in which a fragment of the chromosome is removed


change to a chromosome in which part of the chromosome is repeated


a kind of mutation in which the order of the genes in a section of a chromosome is reversed


change to a chromosome in which a fragment of one chromosome attaches to another nonhomologous chromosome

Down syndrome

A human genetic disease resulting from having an extra chromosome 21, characterized by mental retardation and heart and respiratory defects

Klinefelter syndrome

XXY - males that are characterized by small testes and long legs and enlarged breasts and reduced sperm production

Turner syndrome

Girl with underdeveloped sex organs, girl with only one X

cri du chat

a chromosomal deletion in chromosome 5 that results in children who are mentally retarded, have small heads, and have a cry that sounds like a loud cat; they die at a young age


A genetic abnormality in which a child cannot metabolize phenylalanine, an amino acid, which consequently builds up in the body and causes mental retardation

Tay Sach's Disease

human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accomidation of a certain lipid in the brain. Most common in Ashkenazic Jews.

Cystic fibrosis

genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consquent vulnerability to infection

Huntington's disease

caused by a dominant allele. genetic disorder that causes progressive deterioration of brain cells. symptoms do not appear until the age of 30 or so

Multiple X syndrome

embyros with triple X chromosomes. individuals are phenotypically normal

Sickle-cell anemia

a recessive genetic disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape. Most common in African Americans.

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