Name _____________________________________
Period ______
Genetics and Heredity Outline
What is Genetics?
 Traits are _________________.
 Same hair color, eye color, or skin color.
 Genetics is the science of ______________.
 Heredity is the study of the way ________ are passed on from
_________ to _____________.
Variation
 The __________ an organism inherits is determined during the life
process of ____________.
 More ____________ (differences) are found in _________ reproduction
than by ______________ reproduction.
 In sexual reproduction, the offspring ___________ its parents but is also
____________ from them.
Species and Chromosome Number
 The ______________ number (species chromosome number) is the
same from _____________ to generation within an ________ or species.
 Every ________ will have a different ________________ number.
Human =
Dog =
Pea =
Crayfish =
Cat =
Fruit fly =
Chromosome Arrangement
 In a cell, _____________ are arranged in _______.
 A photograph or chart of ______________ arranged in pairs is called a
______________.
Gregor Mendel
 Today’s knowledge about __________ is a result of genetic
studies started by ________________ in the middle 1800’s.
 Because of his work, he is called the “father of __________.”
 Mendel did not know about _________, but thought that certain
“____________” were responsible for ________ passed from
parents to offspring.
The Gene-Chromosome Theory
 This theory states that _______________ (found in the
_____________ of the cell) are made of small units
called ________.
 Genes carry ___________ information and are found at
specific locations along ____________.
Alleles
 _________ are pairs of _______ that carry the ________ traits and are
found at the _________ locations on pairs of ________________.
 Each chromosome may contain several hundred _________.
Inheritance of Traits
 During _____________, the male and female parents each contribute
genetic information (______) to the _________ (fertilized egg).
 One-half of its genetic information is from its _______ parent and
the other _______ from its ______ parent.
 _________ traits are carried in ____________.
Mendel’s Experiments
 Gregor ________ conducted _________
experiments using common garden pea
plants.
 Mendel ______ (mated) large numbers of
plants.
 Mendel concluded that there were
______ that always appeared (were
expressed) when they were present in an
organism.
 The purebred plants are called the
_________ (P) generation.
 The _________ of a cross between two
parent (P) generation plants are called the first filial (F1) generation.
 The trait that always appears when it is present is called the ______ trait.
 The trait that is hidden by the dominant trait is called the ________ trait.
Genetic Terms
 _____________ Trait - Both ________ for that ______ are the ______.
 A pea plant with two genes for tallness.
 _____________ Trait - Both ______ for that trait are ____ the same.
 A pea plant with one gene for tallness and one for shortness.
 ___________ - The _________ makeup of an organism.
 ___________ - The external _________ of an organism.
 For example, an organism that looks tall can have a genotype that
is pure tall or hybrid tall. This is because whenever the dominant
trait is present, the organism expresses (shows) the dominant trait.
Punnett Squares
Try This Punnett Square
In roses, red is dominant over white.
1. What letter represents the red gene?
2. What letter represents the white gene?
3. Cross two heterozygous red roses.
Describe the phenotype of the offspring.
A Dihybrid Cross
In mice, black is dominant over tan and short tails are dominant over long.
Write the genotype for a heterozygous black, short- tailed mouse.
B = black
b = tan
S = short tails
s = long tails

What are the possible gametes for this mouse?
Each gamete must have one “B” and one “S”
Describe the phenotype of
the offspring.

Gene Linkage
 Today, we now know that _______ are not all inherited independently of
each other.
 Scientists have found that ________ that are located on the same
_______________ tend to be inherited ___________.
 Traits located on the same chromosome are said to show ___________.
Crossing-Over
 Although linked genes are generally
inherited _________, they can become
separated by _____________, which
may occur during a stage of ________.
 During this stage, the four chromatids
sometimes _______ around each other.
 As they separate, the chromatids may
______, exchange segments, and ____.
Incomplete Dominance
 Incomplete dominance or __________ inheritance occurs when the
offspring shows traits that are a ______ or _____ of the two parents.
Inheritance of Sex
 Your ______ (male or female) was determined when your mother’s
____ was fertilized by your father’s _____.
 Humans have one pair of chromosomes, called the ____ chromosomes.
 Sex chromosomes are represented as _____ and ____.
 Egg cells have only ___ chromosomes while sperm carry either an ___
or a ___ chromosome.
 At ___________, _____ X chromosomes produce a ________ (____).
 An X chromosome and a Y chromosome produce a _______ (____).
 In most organisms, it is the ______ that determines the sex of the
offspring.
Sex-Linked Inheritance
 The Y chromosome is _______ than the X chromosome.
 Several of the genes found on the X chromosome are not found on the Y
chromosome.
 The genes on the X chromosome that have no matching genes on the Y
chromosome are called _________________.
 Sex-linked genes are usually __________.
 Two human ________ associated with sex-linked genes are hemophilia
(blood does not clot properly) and color blindness.
 Both of these disorders are more common in _________ than in females.
 This is because the sex-linked recessive gene on the male’s X
chromosome is the only gene the male has for the sex-linked trait.
 A female will not have hemophilia, color blindness or any other sexlined condition, as long as she has ______ normal gene for the trait.
 Females who have one recessive gene for a sex-linked trait are
called “_________” for that trait.
 That means they do not have the disorder, but they ________ the
recessive gene.
 Children of ______ can inherit the sex-linked gene
Sex-Linked Inheritance
Genetics and Heredity Outline – Teacher Guide (Key)
© Lisa Michalek
What is Genetics?
 Traits are characteristics.
o Same hair color, eye color, or skin color.
 Genetics is the science of heredity.
 Heredity is the study of the way traits are passed on from parent to
offspring.
Variation
 The traits an organism inherits is determined during the life process of
reproduction.
 More variation (differences) are found in sexual reproduction than by
asexual reproduction.
 In sexual reproduction, the offspring resembles its parents but is also
different from them.
Species and Chromosome Number
 The chromosome number (species chromosome number) is the same
from generation to generation within an organism or species.
 Every species will have a different chromosome number.
o Human = 46
o Crayfish = 100
o Dog = 48
o Cat = 38
o Pea = 14
o Fruit fly = 8
Chromosome Arrangement
 In a cell, chromosomes are arranged in pairs.
 A photograph or chart of chromosomes arranged in pairs is called a
karyotype.
Gregor Mendel
 Today’s knowledge about genetics is a result of genetic studies started
by Gregor Mendel in the middle 1800’s.
 Because of his work, he is called the “father of genetics.”
 Mendel did not know about genes, but thought that certain “factors”
were responsible for traits passed from parents to offspring.
The Gene-Chromosome Theory
 This theory states that chromosomes (found in the nucleus of
the cell) are made of small units called genes.
 Genes carry hereditary information and are found at specific locations
along chromosomes.
Alleles
 Alleles are pairs of genes that carry the same traits and are found at the
same locations on pairs of chromosomes.
 Each chromosome may contain several hundred genes.
Inheritance of Traits
 During fertilization, the male and female parents each contribute genetic
information (traits) to the zygote (fertilized egg).
o On-half of its genetic information from its male parent and the
other half from its female parent.
 Genetic traits are carried in chromosomes.
Mendel’s Experiments
 Gregor Mendel conducted heredity experiments using common garden
pea plants.
 Mendel crossed (mated) large numbers of plants.
 Mendel concluded that there were traits that always appeared (were
expressed) when they were present in an organism.
 The purebred plants are called the parent (P) generation.
 The offspring of a cross between two parent (P) generation plants are
called the first filial (F1) generation.
 The trait that always appears when it is present is called the dominant
trait.
 The trait that is hidden by the dominant trait is called the recessive trait.
Genetic Terms
 Homozygous Trait - Both genes for that trait are the same.
o A pea plant with two genes for tallness.
 Heterozygous Trait - Both genes for that trait are not the same.
o A pea plant with one gene for tallness and one for shortness.
 Genotype - The genetic makeup of an organism.
 Phenotype - The external appearance of an organism.
o For example, an organism that looks tall can have a genotype that
is pure tall or hybrid tall. This is because whenever the dominant
trait is present, the organism expresses (shows) the dominant trait.
Punnett Squares
Step 1. State the key by using the capital letter of the dominant trait to
represent the dominant gene and the small letter of the dominant trait to
represent the recessive gene.
Step 2. Write the cross and show the gametes.
Step 3. Draw the Punnett square and place the letters for the egg
alleles on one side of the square and the letters for the sperm alleles on
the other side of the square.
Step 4. Write the results next to the square.
Try This Punnett Square
In roses, red is dominant over white.
1. What letter represents the red gene?
2. What letter represents the white gene?
3. Cross two heterozygous red roses.
Describe the phenotype of the offspring.
A Dihybrid Cross
 In mice, black is dominant over tan and short tails are dominant
over long. Write the genotype for a heterozygous black, shorttailed mouse.
o B = black
o b = tan
o S = short tails
o s = long tails
A Dihybrid Cross
 B b S s = heterozygous black, short
 What are the possible gametes for this mouse?
 Each gamete must have one “B” and one “S”
Describe the phenotype of the
offspring.
Gene Linkage
 Today, we now know that traits are not all inherited independently of
each other.
 Scientists have found that traits that are located on the same
chromosome tend to be inherited together.
 Traits located on the same chromosome are said to show linkage.
Crossing-Over
 Although linked genes are generally inherited together, they can become
separated by crossing-over, which may occur during a stage of meiosis.
 During this stage, the four chromatids sometimes twist around each
other.
 As they separate, the chromatids may break, exchange segments, and
rejoin.
Incomplete Dominance
 Incomplete dominance or blending inheritance occurs when the
offspring shows traits that are a blend or mix of the two parents.
Inheritance of Sex
 Your sex (male or female) was determined when your mother’s egg was
fertilized by your father’s sperm.
 Humans have one pair of chromosomes, called the sex chromosomes.
 Sex chromosomes are represented as X and Y.
 Egg cells have only X chromosomes while sperm carry either an X or a
Y chromosome.
 At fertilization, two X chromosomes produce a female (XX).
 An X chromosome and a Y chromosome produce a Male (XY).
 In most organisms, it is the sperm that determines the sex of the
offspring.
Sex-Linked Inheritance
 The Y chromosome is smaller than the X chromosome.
 Several of the genes found on the X chromosome are not found on the Y
chromosome.
 The genes on the X chromosome that have no matching genes on the Y
chromosome are called sex-Linked genes.
 Sex-linked genes are usually recessive.
 Two human diseases associated with sex-linked genes are hemophilia
(blood does not clot properly) and color blindness.
 Both of these disorders are more common in males than in females.
o This is because the sex-linked recessive gene on the male’s X
chromosome is the only gene the male has for the sex-linked trait.
 A female will not have hemophilia, color blindness or any other sexlined condition, as long as she has one normal gene for the trait.
o Females who have one recessive gene for a sex-linked trait are
called “carriers” for that trait.
o That means they do not have the disorder, but they carry the
recessive gene.
o Children of carriers can inherit the sex-linked gene.