Introduction to Heredity

What is Heredity? Heredity is the passing of traits from parents to offspring Genetics is the study of heredity

Gregor Mendel Known as the “Father of Genetics” Austrian Monk Born in 1822

Mendel’s Work Experimented with “True Breeding” pea plants in his garden True Breeding –Plants that produce identical offspring when allowed to self pollinate –AKA “Purebred” Discovered how traits are passed from parent to offspring in sexual reproduction

What is a Trait? A trait is a notable feature or quality in a person ah.edu/content/begin/ traits/tour_trait.htmlhttp://learn.genetics.ut ah.edu/content/begin/ traits/tour_trait.html

Traits Inherited vs. Acquired InheritedAcquired Received from biological parent –Eye color –Height –Blood Type Acquired during lifetime; not inherited –Ability to ride a bike –Scars –Pierced ears Some traits can be both! Skin Color Received genes for skin color from both parents Amount of time in the sun affects skin color

Genes A gene is a unit of heredity Occupies a specific location on a chromosome Codes for or determines a specific trait –Most traits are not coded for by just one gene

Genes and Chromosomes Genes are located on chromosomes Chromosomes come in pairs –Each pair is called a homolog On each homolog are sites where specific genes are located

Alleles Alleles are various forms of the same gene. Example 1: –Gene: Eye Color –Alleles: Brown, Blue, Hazel Example 2: –Gene: Seed Color –Alleles: Green, white, yellow

Mendel’s Work, continued Mendel also performed experiments with hybrid plants –Hybrids - Plants that were produced by parents with different traits In these experiments, he discovered that traits are inherited by parents passing alleles to their offspring

Mendel’s Conclusions (Principles of Heredity) Individuals carry two alleles for each trait, but only pass down one to their offspring One allele is dominant over another

Heredity Day 2 Questions to ask yourself….. + How do alleles interact to produce traits? + How does my combination of traits make me unique? + How do my traits connect me to other people?

Alleles determine traits An organism’s traits are controlled by the alleles it inherits from its parents Mendel discovered that there are two types of alleles: –Dominant –Recessive

Dominant Alleles Dominant Allele: an allele whose trait is always shows up in the organism when the allele is present –Expressed if only one is present –Example: Brown Eye Color

Recessive Alleles Recessive Allele: an allele whose trait is hidden whenever the dominant one is present –Can only be expressed if two are present –Example: Blue Eye Color

Alleles are represented by symbols Dominant Represented by a capital letter Recessive Represented by the lower case letter W w

Alleles interact to produce traits Each parent contributes ONE allele for a given trait The combination of alleles from parents can result in varying traits in their offspring Alleles for widows peak chromosomes W w

Genetic Terminology Genotype: An organisms genetic makeup, or alleles an organism has for a trait is its genotype –Ww, Bb, bb, ww, etc Phenotype: An organism’s physical appearance, or visible traits is its phenotype. –Widow’s peak, brown eyes, blue eyes, straight hairline, etc

Example: Flower Color Genotype Pp Alleles for flower color Phenotype Physical appearance

Genetic Terminology Terms used to describe an organisms genotype –Heterozygous – an organism that has two different alleles for a trait is said to be heterozygous Example: Ww, Bb –Homozygous – An organism that has two identical alleles for a trait is said to be homozygous Example: WW, ww, BB, bb

Using Genetic Terminology Homozygous Recessive Homozygous Dominant Heterozygous

Using Genetic Terminology Homozygous Recessive Homozygous Dominant Heterozygous

Using Genetic Terminology Homozygous Recessive Homozygous Dominant Heterozygous

Using Genetic Terminology Homozygous Recessive Homozygous Dominant Heterozygous

Using Genetic Terminology Homozygous Recessive Homozygous Dominant Heterozygous

Can you determine an organism’s genotype just by looking at it?

Traits in a population Observable characteristics we inherit from our parents Some traits are common in a population, while others are not Every person has a different overall combination of traits that make them unique