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Genetics
Where do you think the
directions for making you
came from?"
Inheritance: what makes youYOU!
 Inheritance
occurs through sexual
reproduction.
 During sexual reproduction, a cell that
contains genetic information from the
mother and father join to form a
completely new cell.
 Each parent organism contains one-half
of the genetic material need to create a
new organism.
DNA
Stands for: Deoxyribonucleic acid
 It is where genetic information is stored.
 It determines every inherited physical
characteristics of every living thing.
 It controls how the cell replicates and
functions.
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What is a Gene?
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A short unit of DNA that codes for a particular trait,
like a recipe.
Genes are responsible for the inherited
characteristics that distinguish one individual from
another.
Genes for a specific trait come in pairs.
There are approximately 30,000 genes in each cell
of the human body.
The combination of all genes make up the blue
print for the human body and its functions
A person’s genetic makeup is called a genotype
The physical expression of genes is called
phenotype.
Juicy Science Question?
 What
would happen if something went
wrong in the DNA sequence?
Chromosomes
 In
the nucleus of each cell, the DNA
molecule is packaged into thread-like
structures called chromosomes.
 Chromosomes come in pairs. Each
member in the pair is called
a homolog, or sister chromatid.
 Genes have a specific location on the
chromosome.
What is an Allele?
 One
gene from the pair of homologs is
called an Allele.
 An alternate form of a specific gene.
 For example, one homolog of a
chromosome may have an allele for
Regular height (A) and the other homolog
May have an allele for short height (a).
 The alleles on a pair of homologs may or
may not be different.
Chromosome Number
 Each
species has a characteristic number
o chromosomes.
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Chimpanzees: 24 chromosome pairs
Fruit flies have 4 chromosome pairs
Humans have 23 chromosome pairs
 Heredity
is the passing of traits from one
generation to another.
 Heredity determines certain specific
characteristics of plants and animals.
 Animals can inherit behavioral, mental,
and physical traits.
Another word for heredity is inheritance.
Inherited Traits
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Characteristics that are passed from parent to
offspring.
For example:
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Eye color
Eye shape
Hair type
Face shape
Some traits are dominant and some are
recessive.
Dominant Traits
A
trait that will always be expressed in the
phenotype.
 These are represented by CAPITAL letters.
For example, A.
Content Check
 What
is the difference between
phenotype and genotype?
 Phenotype=
physical characteristic
displayed. Ex, eye color
 Genotype= Set of genes carried by an
organism
Recessive Trait
A
trait that will only be expressed in the
phenotype if two recessive alleles are
present.
 Represented by lowercase letters.
 For example, a.
 The genotype aa would express the
recessive trait.
 IN THE PRESENCE OF A DOMINANT TRAIT,
THE RECESSIVE TRAIT WILL NOT BE
EXPRESSED.
Sex Linked Traits
 Males
have an XY chromosome combination
 Females have an XX chromosome combination
 Genes that are carried by either sex chromosome
are said to be sex linked
 X-linked diseases usually occur in males. Males
have only one X chromosome. A single recessive
gene on that X chromosome will cause the
disease.
 Austrian
Monk & the “father” of genetics
 Before he became a Monk, he attended
university to study science and Math.
 He studied pea plants to prove the
existence of genes.
 He hypothesized that genes
Controlled several different traits:
Height, seed shape, seed color,
and flower color are a few examples.
Punnett Squares
 Mendel
observed seven traits in pea plants.
 Mendal realized that each plant must have “two
factors” for each possible trait, one factor from
each parent.
 Some traits like dwarf height could be masked.
(recessive)
 A Punnett square helps diagram the probability of
each possibility genotype and phenotype in a
generation.
 Mendel described the pea plant factors as alleles
Punnett Squares
 In
a Punnett square, the top of the table
shows the alleles provided by one parent.
 The alleles for the other parent are
placed along the left side of the table.
 One allele from each parent is placed in
the individual squares, forming a new
gene pair.
 The individual squares show the
possibilities of allele pairs in the offspring.
Punnett Square Example
The cross Tt x tt:
t
t
T
Tt
Tt
t
tt
tt
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As the Punnett square shows, TT, Tt, and tt are all
possible genotypes for the height of the offspring.
The offspring with the genotypes TT and Tt will
have a phenotype of tall; the offspring with the
genotype of tt will have a phenotype of short.
If the two alleles are the same (TT or tt), the
genotype is considered purebred. If the two
alleles are different (Tt), the genotype is
considered hybrid.
This example shows the inheritance of a single
characteristic (height). A cross that shows the
inheritance of a single characteristic is known as
a monohybrid cross.
It is sometimes difficult to predict certain traits in
humans (for example hair color or eye color)
because there may be several different genes
that control these traits.