Genetics Definitions

Question 1

Gene

Answer 1

sequence of DNA that represents fundamental unit of genetic expression for a gene product (usually protein). This gene is responsible for a feature (character).

Question 2

Locus (Loci)

Answer 2

specific location (site) of a gene in a chromosome

Question 3

Alleles

Answer 3

alternative forms of a gene for a specific character. Alleles occupy the same loci (locus) in homologous chromosomes

Question 4

homozygous

Answer 4

2 alleles, for a particular character, are identical

Question 5

heterozygous

Answer 5

2 alleles, for a particular character, are not identical

Question 6

dominant allele

Answer 6

the allele (gene) which expresses its character in both homozygous and heterozygous conditions (AA) (Aa)

Question 7

Recessive allele

Answer 7

the allele which does express its character only homozygous condition (aa)

Question 8

autosomal

Answer 8

expression of allele (gene) in autosomes (chromosomes 1-22)

Question 9

x-linked

Answer 9

expression or inheritance of characters through X-chromsomes

Question 10

phenotype

Answer 10

observable features, outward appearance, manifestations/physical characteristics
Example: brown eyes, curly hair, HbA, HbS, morphological abnormalities

Question 11

Genotype

Answer 11

genetic set up (pattern of alleles) in autosomes or sex chromosomes for a particular character.
Example: BB=brown (homozygous dominant) eye color
bb=blue (homozygous recessive) eye color
Bb=brown (heterozygous) eye color

Question 12

allelic heterogeneity

Answer 12

genetic disease caused by different types of mutation in the same gene
Example: Cystic Fibrosis

Question 13

locus heterogeneity

Answer 13

genetic disease caused by mutation at one or different locus/loci
Example: albinism

Question 14

complete penetrance

Answer 14

mutant dominant gene is capable of causing abnormal phenotypic manifestation

Question 15

reduced (incomplete) penetrance

Answer 15

mutant dominant gene is incapable of causing abnormal phenotypic manifestations. Have gene but not expressing it.

Question 16

pleiotropy

Answer 16

appearance of multi system (3 or more) phenotypic abnormalities in a genetic disease

Question 17

variable expression

Answer 17

variation of abnormal phenotypic expression among individuals affected w/same genetic diseases (mild, moderate, severe)

Question 18

proband/propositus/index case

Answer 18

affected member of a family

Question 19

consultant

Answer 19

the person (who may or may not be affected) who consults the genetic counselor

Question 20

sibs

Answer 20

brother and sister of the affected family

family of sibs called sibship

Question 21

consanguinity

Answer 21

couples having 1 or more ancestors in common

Question 22

isolated

Answer 22

only one affected member in a family

Question 23

sporadic

Answer 23

disorder is due to new mutation

Question 24

relatives:

1. First degree
2. Second degree
3. Third degree

Answer 24

1. parents, sibs, and offspring of the proband
2. grandparents, uncles, aunts, grandchildren, nephews, and nieces
3. first cousins