Download Intro to Genetics - Effingham County Schools

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.ut
ah.edu/content/begin/
traits/tour_trait.html
Traits
Inherited vs. Acquired
Inherited
•Received from
biological parent
–Eye color
–Height
–Blood Type
Acquired
•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
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
Recessive
Represented by a capital letter
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
W
Alleles for
widows peak
w
chromosomes
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
Phenotype
Pp
Alleles for flower
color
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