Human Genetics: Dominant & Recessive Traits

The physical characteristics below are common genetic traits inherited from one generation to the next: 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: Review the following slides that contain:  Definition and images of each genetic trait  Identification of the Dominant / Recessive trait Human Genetics: Dominant & Recessive Traits

Allele: An alternate form of a gene. Alleles occur at loci on chromosomes Dominant: Only one allele at a locus is expressed. The other (recessive gene) is suppressed. 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 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

Free vs. Attached Earlobes Free earlobes (dominant trait) hang below the point of attachment to the head. 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. 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. 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. 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): 1. Hold your hands together as if you are covering your face. 2. 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 the DOMINANT allele can roll their tongues into a tube shape. People with 2 recessive versions are non-rollers 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 the DOMINANT allele can roll their tongues into a tube shape. People with 2 recessive versions are non-rollers 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 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 People lacking hair in the middle segments of the finger have 2 recessive versions of the gene

100% Environmental Struck by lightning Infection Weight Cancer Diabetes Height Sex, Down syndrome, achondroplasia 100% Genetic Hair Colour Not Everything is Genetic

Co-dominant The alleles for curly hair and straight hair are examples of alleles for a trait that are codominant. 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 curly hair are homozygous for curly hair alleles. Individuals with straight hair are homozygous for straight 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. 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. 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. A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and O type.ABO blood group systemABO blood group system 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. 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.

Karotype

X-linked recessive Many more males than females show the disorder. Many more males than females show the disorder. All the daughters of an affected male are “carriers”. All the daughters of an affected male are “carriers”. None of the sons of an affected male show the disorder or are carriers. None of the sons of an affected male show the disorder or are carriers. e.g., hemophilia e.g., hemophilia

X-linked

X-linked dominant Affected males pass the disorder to all daughters but to none of their sons. 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 Affected heterozygous females married to unaffected males pass the condition to half their sons and daughters e.g. fragile X syndrome e.g. fragile X syndrome

X-linked Dominant