Chapter 20 - Patterns of Genetic Inheritance Part 1

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




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