TEST BANK FOR HUMAN BIOLOGY, 12TH EDITION– SYLVIA MADER
Chapter 21 - DNA Biology and Technology
Chapter 20 - Patterns of Genetic Inheritance
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Chapter 7 - Patterns of Genetic Inheritance - Part 1
Genotype
Refers to the genes on chromosome that codes for specific trait in an individual. They exist in
specific position (locus) on chromosomes
An allele is an alternate forms of a specific gene at the same locus of chromosome (e.g.,
allele for unattached earlobes and allele for attached earlobes, allele for blue eye and allele
for brown eye)
Alleles occur in pairs, can be either dominant or recessive
Dominant gene (allele): Only one copy of the allele needs to be present in both
chromosomes for the trait to be expressed (Tt or TT)
Recessive allele: Only expressed when both alleles are present (tt)
Homozygous Dominant Genotype: Consists of 2 dominant alleles (TT)
Homozygous Recessive Genotype: Consists of 2 recessive alleles (tt)
Heterozygous Dominant Genotype: Consists of 1 dominant allele and 1 recessive allele
(Tt)
Alleles are designated by one-letter abbreviation
1
, Dominant allele is assigned an uppercase letter (T)
Recessive alleles assigned a lowercase letter (t)
Phenotype
The physical expression (appearance of trait) of the genotype
Genotype Phenotype
EE Unattached earlobe
Ee Unattached earlobe
ee Attached earlobe
2
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