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

• http://learn.genetics.utah.edu/content/begin/traits/tour_trait.html

TraitsInherited vs. Acquired

Inherited Acquired

•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 ColorReceived 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 ColorGenotype

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