Biological Diversity - Genetics and Variation

Biological Diversity: Genetics and Variation

Variation of Characteristics within a Species

• Variation: Differences in characteristics within a species.

  • Examples include:

    • Hand clasping preference.

    • Length of human hands.

• Discrete Variation: Characteristics with a limited number of possibilities.

  • Example: Hand clasping preference is an example of discrete variation

• Continuous Variation: Characteristics that vary on a continuum.

  • Example: The length of human hands varies on a continuum

Genetics and Heredity

• Heredity: The passing on of traits from parents to their offspring.
• Genetics: The branch of science that studies heredity.

Inherited Variations

• Continuous Variation

  • Traits with a range of possibilities.

  • Examples:

    • Height
    • Hand span
    • Skin color
    • Hair color

• Discrete Variation

  • Characteristics with a limited number of possibilities.

  • Examples:

    • Ability to curl your tongue (either you can or you cannot)
    • ABO blood group
    • Sex (Male or Female)

Examples: Continuous or Discrete?

• Discrete: Blood Type, Eye Color, Gender, Attached earlobes, Pointed hairline (Widow’s Peak), Left thumb on top of clasped fingers, No middigital hair
• Continuous: Weight, Medium height, Brown hair

IQ as Continuous or Discrete Variation

• IQ is a continuous variation because it exists on a spectrum, with individuals having a range of possible IQ scores.

Dominant and Recessive Genes

• Dominant Gene: A gene that is always expressed when present.
• Recessive Gene: A gene that is only expressed when two copies of the gene are present.
• Example: A black bear with white fur expresses a recessive trait.

Dominance vs. Frequency

• Dominance and frequency are not the same.
• The frequency of a trait can vary from population to population.
• Example: Having six fingers is a dominant trait but is relatively rare.

Examples of Dominant and Recessive Traits

• Dominant Traits: Baldness (in males), Presence of body hair, Bent pinkie, High blood pressure rate, Rh factor positive (+), Absence of cleft in chin, Left thumb over right thumb when crossing thumbs, Presence of dimples, Second toe longer than first toe, Normal hearing , Definite Free Earlobes, Ability to roll tongue (side edges up), Long eyelashes, Presence of freckles, Astigmatism, Presence of Hitchhiker's thumbs, Widow's peak, Right-handedness, Broad lips, Presence of Mid-digital hair, Presence of Mongolian eye fold, Roman nose (bump).
• Recessive Traits: Not able to bend pinkie, Little body hair,Low blood pressure rate, Rh factor negative (-), Presence of cleft in chin, Right thumb over left thumb when crossing thumbs, Absence of dimples, First toe longer than second toe, Tone deafness, Attached Earlobes, Inability to roll tongue, Short eyelashes, Normal Vision, Absence of Webbed fingers, Absence of Hitchhiker's thumbs, Straight Hairline, Normal hair color, Left-handedness, Thin lips, Absence of Mid-digital hair, Absence of Mongolian eye fold, and Straight nose.

Punnett Squares

• Representing Traits: Use a capital letter for a dominant trait (e.g., $B$ for brown eyes) and a lowercase letter for a recessive trait (e.g., $b$ for blue eyes).
• Genes exist in pairs: one from each parent.
• Possible combinations: $BB$, $Bb$, $bb$.

Punnett Square Examples

• Example 1: Parents with brown eyes ($BB$) and blue eyes ($bb$).
• Example 2: Parents with red hair ($bb$) and brown hair ($Bb$).

Example Punnett Square

• Parent 1: $Bb$ (Brown eyes)
• Parent 2: $bb$ (Blue eyes)
• Possible offspring genotypes: $Bb$, $bb$
• Probability of offspring having blue eyes: 50%

Genotype vs. Phenotype

• Genotype: The genetic makeup (e.g., $BB$, $Bb$, $bb$).
• Phenotype: The physical expression of the trait (e.g., brown eyes, blue eyes).

Nature vs. Nurture

• Not all characteristics are inherited; some depend on the environment.
• Scars and injuries are not caused by genetics.
• A person’s weight is influenced by genetics, diet, and activity level.
• Nature: A person’s genetics (e.g., height).
• Nurture: Environmental influences (e.g., hairstyle, makeup, scars).

Mutations

• Changes to DNA (genetic material) caused by environmental factors or random errors.

Mutations and Mutagens

• Mutagens: Factors that cause mutations (e.g., X-rays, ultraviolet rays, cosmic rays, some chemicals).
• Mutations in individual cells can cause cancers.
• Mutations increase variation within a species; they are usually unfavorable, but sometimes harmless or beneficial.

Mutagens

• Mutagens can boost abilities.

Review Questions

• Is the variation in weight in human populations an example of discrete or continuous variation? Explain.
• Is human skin color purely an inherited trait? Explain.