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Human Genetics: Dominant & Recessive Traits. Human Genetics: Dominant & Recessive Traits. The physical characteristics below are common genetic traits inherited from one generation to the next: Free vs. Attached Earlobes Straight vs. Curved Thumbs Bent vs. Straight Pinky
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Human Genetics:Dominant & Recessive Traits • The physical characteristics below are common genetic traits inherited from one generation to the next: • Free vs. Attached Earlobes • Straight vs. Curved Thumbs • Bent vs. Straight Pinky • Review the following slides that contain: • Definition and images of each genetic trait • Identification of the Dominant / Recessive trait
Dominant: Only one allele at a locus is expressed. The other (recessive gene) is suppressed. Recessive: An allele that is suppressed in the presence of a dominant gene. If the two recessive alleles occur at a locus, then the trait is expressed Allele: An alternate form of a gene. Alleles occur at loci on chromosomes
Free vs. Attached Earlobes • Free earlobes(dominant trait) hang below the point of attachment to the head. • Attached ear lobes(recessive trait) are attached directly to the side of the head.
Straight vs. Curved Thumbs • Straight thumbs (dominant trait) can be seen as nearly a straight line and may contain a slight arch when viewed from the side as in the illustrations. • Curved thumbs (recessive trait) can be seen as part of a circle.
Bent vs. Straight Pinky Bent pinky (dominant trait) vs. Straight pinky (recessive trait): • Hold your hands together as if you are covering your face. • If the tips of the pinkies (or baby fingers) point away from one another, the pinkies are bent(dominant trait).
Tongue rolling • People with the DOMINANT allele can roll their tongues into a tube shape. • People with 2 recessive versions are non-rollers
Tongue rolling • People with the DOMINANT allele can roll their tongues into a tube shape. • People with 2 recessive versions are non-rollers
Thumb Crossing • In a relaxed interlocking of the fingers, left thumb over right results from having 1 or 2 copies of the dominant version of the gene. People with 2 recessive places right thumb over left
Mid Digit Hair • People lacking hair in the middle segments of the finger have 2 recessive versions of the gene
Not Everything is Genetic 100% Environmental Struck by lightning Infection Weight Hair Colour Cancer Diabetes Height 100% Genetic Sex, Down syndrome, achondroplasia
Co-dominant • The alleles for curly hair and straight hair are examples of alleles for a trait that are codominant. • Individuals with curly hair are homozygous for curly hair alleles. • Individuals with straight hair are homozygous for straight hair alleles. • Individuals who are heterozygous, with one of each allele have wavy hair, which is a blend of the expressions of the curly and straight hair alleles.
Codominant Continued • In codominance, neither phenotype is completely dominant. Instead, the heterozygous individual expresses both phenotypes. • A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and O type . • O type is recessive to both A and B. The A and B alleles are codominant with each other. When a person has both an A and a B allele, the person has type AB blood.
X-linked recessive • Many more males than females show the disorder. • All the daughters of an affected male are “carriers”. • None of the sons of an affected male show the disorder or are carriers. • e.g., hemophilia
X-linked dominant • Affected males pass the disorder to all daughters but to none of their sons. • Affected heterozygous females married to unaffected males pass the condition to half their sons and daughters • e.g. fragile X syndrome
