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Heredity and Genetics
Chapter 5
Dimples
Heredity
 Traits – things that make
a person unique
Eye color and shape,
nose shape, cheekbone structure, skin
color, hair color etc
 Heredity – The passing of traits from
parent to offspring
Genetics
 Genes on chromosomes
control the traits that show
up in an organism
 Alleles – the different forms
of a trait a gene might have
 http://www.brainpop.com/
health/geneticsgrowthandde
velopment/genetics/
Genetics!
 During meiosis, a pair of chromosomes
separates and the alleles move into separate sex
cells
 Each sex cell now contains one allele for each
trait
Genetics!!
 Genetics – the study
of how traits are
inherited
 Gregor Mendel –
the father of genetics
 The first to use
math and
probability to
explain heredity
and trace one trait
for several
generations
Hybrids. And I don’t mean Prius
 Hybrid - receives different genetic information
(different alleles) for a trait from each parent
 Dominant allele – covers up or dominates the
other trait
 Recessive allele – the trait is not expressed; it
seems to disappear
 Purebreds – an organism that always produces the
same traits generation after generation
 http://www.brainpop.com/science/cellularlifeandgenetics/heredity/
Square Dancing!
 Probability helps you predict
the chance of something
happening
 A Punnett Square can help you predict what
an offspring will look like
 Capital Letters stand for dominant alleles
 Lowercase Letters stand for recessive alleles
Complete this Punnett Square
 Genes for height of plants:
T =
t =
•What are the
chances that the
plant will be tall?
•What are the
chances that the
plant will be
short?
GENO and PHENO
 Genotype – the
genetic makeup of an
organism. All the
genes!
 Homozygous – an
organism with two
alleles for one trait
that are the same.
(Written TT)
GENO and PHENO
 Heterozygous – an organism with two
alleles for one trait that are different
(Written Tt)
 Phenotype – the way an organism looks
and behaves as a result of its genotype
Review
 How do heredity and genetics explain
why people are different?
 What’s the difference between a
dominant allele and a recessive allele?
Questions
 People are hybrids; we receive different genetic
information from each of our parents. Our parents carry
different alleles for the same trait. These alleles can
combine in different ways to create different traits in
people.
 A dominant allele is expressed if an allele pair is
homozygous or heterozygous. A recessive allele is
expressed only when an allele pair is homozygous
recessive
Genetics Since Mendel
 Incomplete Dominance
is a situation where neither
allele is dominant over the
other
 The phenotype produced is
intermediate between the
two parents
Incomplete Dominance
 With incomplete
dominance, a
cross between
organisms with
two different
phenotypes
produces offspring
with a third
phenotype that is a
blending of the
parental traits.
Multiple Alleles
 Some traits are controlled by more than two alleles
 More than two alleles that control a trait are called multiple
alleles
 Traits controlled by multiple alleles produce more than three
phenotypes
Polygenic Inheritance
 Polygenic Inheritance occurs when a group of gene pairs acts
together to produce a trait
 Height
 Eye color
 Skin color
 Hair color is determined by 3-6 pairs of genes
Environmental Influences
 Genes determine many of your traits, but you might be able
to influence their expression by the decisions you make.
 Example: Some people might be more prone to skin cancer
than others.
 Limit sun exposure; lessen risk of cancer
Human Genes and Mutations
 Mutation – when gene changes and results in a trait being
expressed differently
 Ex: A butterfly’s offspring being different colors or blending in
better with environment
 Genetic disorders
Chromosome Disorders
 Every organism has a specific number of chromosomes that
needs to be inherited
 Mistakes in meiosis can give too little or too many
chromosomes
 Problems can occur if the wrong number of chromosomes is
inherited
 Changes in chromosomes are usually fatal
 Some diseases are the result of chromosome
changes; Down’s Syndrome
Recessive Genetic Disorders
 Some diseases are caused by two recessive genes carrying a
mutation
 The 2 heterozygous parents don’t express the disease because
their dominant gene covers it up
 Child expresses the disorder because each infected parent
gave their infected recessive gene
 Ex: Cystic Fibrosis
Gender Determination
 Male Chromosomes: XY
 Female Chromosomes: XX
Sex-Linked Disorders
 Some inherited disorders are linked
to the X or Y chromosomes
 Example: Hemophilia is located on
the X chromosome
 Males only have 1 X
chromosome, so if their X has the
hemophilia gene, it gets expressed
 Females have 2 X chromosomes,
so they have to have the
hemophilia on each X
chromosome to express it
Why is Genetics Important?
 Genetic
Engineering
 Biological and
chemical methods
to change the
arrangement of
DNA
 Helps to produce
large amounts of
medicine
 Improve crop
production
Gene Therapy
 A normal allele is
replaced in a virus
and then delivers
the normal allele
when it infects its
target cell
 Gene Therapy
helps to cure
some inherited
diseases