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Gene Expression: One gene………one enzyme…… polypepetide

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QOD: Taste your PTC paper and determine if you are a “taster” or a “non-taster”. If you are unsure, you are probably a non-taster…..believe me, you will know if you are a taster!Based on your phenotype for this trait, identify and record) your phenotype and genotype or genotype possibilities for this trait .“Non-taster” allele is recessive (a)“Taster” allele is dominant (A)
“Tasters” may have an allelic combination of AA or Aa.“Non-tasters” must have an allelic combination of aa.
Pedigree- a diagram used to show/determine the allelic combinations of individuals for a trait as inherited through several generations of a family.
Genetic Disorders:Sex-linked disorders:Hemophilia (recessive)Duchenne Muscular Distrophy (recessive)Autosomal genetic disorders:Sickle Cell Anemia (codominant)PKU (recessive)Tay-sachs (recessive)Cystic Fibrosis (recessive)Huntington’s (dominant)
Crossing over- Responsible for recombination between linked genes - genes on the same chromosome. The closer the genes are to one another, the less frequently they recombine.Crossing over frequency is proportional to distance between genes.

Gene Expression:

One gene………one enzyme…… polypepetide

*** Each gene controls the synthesis of one polypeptide which is affected by one enzyme

Gene Linkage-Genes close together on same chromosome are called linked genes. Linked genes do not exhibit independent assortment.
Human polygenic traits include:Height Weight Eye Color Intelligence Skin Color Many forms of behavior
Principle of Segregation and Recombination-“factors” (now known to be alleles) that occur in pairs are separated from each other during gamete formation and recombined during fertilization.

The inheritance of traits and their expression vary. Some traits are very obvious, while others may not be so obvious.

Most traits have two possible alleles, while others have many alleles.

Incomplete dominance: where two traits are equally dominant —genotype is always obvious from the phenotype ex. Four o’clock flowers

Co-dominance: both allelles present are expressed ex. Roan cattle

Multiple alleles: 3 or more alleles inheritable ex.blood type and eye color both have different allele combinations due to their being different combinations for expression.

Sex-linked traits: these are traits that are carried specifically on the X or Y chromosomes


Since females are XX, they always have two alleles for each sex-linked trait- one on each X chromosome. If the two alleles are different for a trait, (one dominant , one recessive) the recessive trait will not be expressed phenotypically.Females heterozygous for a sex-linked trait are called “carriers”
Males are XY. They can have only one allele for each sex-linked trait. Therefore, one recessive allele on the X chromosome of a male will always be expressed.
In Kleinfelter's Syndrome, the man has a genotype of XXY; phenotypically, these individuals tend to have small external genitalia and gynecomastia (breast development).In Triple X Syndrome, the woman has a genotype of XXX; phenotypically these individuals appear normal, although some degree of mental retardation may be present.In Turner’s Syndrome, the woman has a genotype of X; these individuals tend to be shorter than average and are usually infertile, or unable to conceive a child, because of a loss of ovarian function. Other features of Turner syndrome vary among affected females and can include webbing of the neck, puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, heart defects, and kidney problems.In XYY males, the male has a genotype of XYY; phenotypically, these individuals, tend to be tall and have severe acne, have a slight decrease in intelligence and have a possible predisposition for violence.