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Genetics and
Heredity
Chapter 5
Characteristics
 Species Characteristics
 Traits or features that every member of the species possess
 Individual Characteristics
 Distinguishing or unique features that a person or organism
has that sets them apart from others of their own species
 Genes
 Are specific segments of DNA that code for the proteins that
make us unique
 We are not only a combination of both our genes
(physical makeup) and our environment but our spiritual
nature or soul
Mechanism of Heredity
 Genetics or the study of heredity (passing on of traits
from parent to offspring) is both the oldest and one of
the newest of the biological sciences
 Biblical – selective breeding of cattle
 Babylonians and Assyrians – breeding and improvement of
plants
 Greeks – mixing of blood “pure bloods” and “blood
relatives”
 Gregor Mendel – pairs of “factors” in organisms were
divided and passed on to next generation
Inheriting Traits
 Generally, genes on a chromosome control
what traits show up in an organism
 Each parent has two genes for a trait. These
specific genes are called alleles.
 The different forms of a trait that a gene may
have are called alleles (uh- LEELZ)
Chromosomes
 Chromosome
 Long strand of DNA that is coiled around protein histones
when not being used to make RNA or to move the genetic
material during cell division
 Made of two identical sister chromatids
 Humans have 23 pairs of chromosomes or one set from
each parent
 These pairs are known as homologous chromosomes
 Each homologue (chromosome from one parent) has the
same type of genes as the other but different ALLELES
Chromosomes continued
Chromosomes cont.
 When a cell has homologous chromosomes or 2 sets it is said
to be diploid or 2n
 Humans have a diploid number of 46 (23+23)
 22 autosomal or non-sex chromosomes
 2 sex chromosomes – determine gender and gender characteristics
 Watermelons  2n=22
 Dogs  2n = 78
 Jumping ant  2n= 2
 When cells have only one set of chromosomes they are known
as haploid or n
 When cells have multiple sets of chromosomes (3+) they are
known as polyploid
 Adder’s tongue fern  2n= 1,260
Inheriting Traits
 During Meiosis, the alleles for different traits (located on
different Chromosomes) are mixed up (crossing over) and
separated randomly (gene segregation) to insure that the
offspring will be a genetically diverse individual
 When a pair of chromosomes separate during
Meiosis, alleles for each trait also separate into
different, haploid sex cells or gametes
 Males- produce sperm (spermatogenesis)
 Females- produce eggs (oogenesis)
 Genes are passed on once Meiosis has created gametes
and those gametes unite through fertilization to form a
diploid zygote
Gregor Mendel – The Father of
Genetics
 Gregor Mendel began
experimenting with garden
peas at his monastery in
Austria in 1857
 Mendel made careful use of
scientific methods, which
resulted in the first recorded
study of how traits pass from
one generation to the next
known as Mendelian Genetics
Mendelian Genetics
 In the 34 varieties of pea seeds that he
planted, Mendel made note of 7 opposing
traits
 Height, seed color, seed texture
 Mendel was the first to track one trait
through several generations
 Since the flowers of the pea plants were
easily manipulated he was able to crosspollinate the plants by hand
 What was the benefit of cross-pollination?
Mendelian Genetics
 In his experiments, Mendel
used the pollen from
purebred tall plants to
pollinate by hand the flowers
of purebred short plants
 The offspring were ALL tall
pea plants…
Mendelian Genetics
 To explain the outcome of this experiment, as
well as the similar results he obtained when
crossing peas with other sets of opposing
characteristics Mendel proposed several
concepts – many now have been scientifically
validated
 Concept of Unit Characteristics
 Concept of Dominant and Recessive
 Concept of Segregation
1. Concept of Unit Characteristics
 This Concept states that an organism’s characteristics
or physical traits are controlled by factors or genes
that occur in pairs
 Genes (segments of DNA) are found in cells and
responsible for inherited features
 Genes are located on chromosomes
 Most organisms have homologous pairs of
chromosomes or one set from each parent
2. Concept of Dominant and Recessive
 Mendel called the trait that expressed
itself when genes for 2 opposing
traits are present the Dominant trait
(caused by a dominant gene)
 In pea plants this was the allele for
Tall height
 The trait that was masked or hidden
was known as the recessive trait
(caused by a recessive gene)
 In pea plants this was the allele for
short height
3. Concept of Segregation
 Mendel reasoned that when a cell forms gametes, the
genes separate (segregate) so that there is only ONE
gene for each characteristic in each gamete
Genetic Terminology
 the genotype, or genetic makeup, of an
organism.
 The actual genes, represented by letters
 Example: Tt, TT, tt
 The way an organism looks or behaves is
a result of its genotype is its phenotype
(physical traits)
 Example: Tall plant, short plant
Genetic Terminology
 Purebred- an organism that always produces
the same trait, generations after generations; it
also has two alleles that are the SAME
 Also called homozygous
 Ex. bb, TT,
 Hybrid- an organism that has two DIFFERENT
alleles for a trait
 Also called heterozygous
 Bb, Tt, Dd
Genetic Terminology
 Cross – a controlled mating or breeding of
two organisms
 In genetic problems a cross shows the
genotypes of both parents
 BB x bb
 Monohybrid cross – a cross between
individuals that deals only with ONE set of
alleles
Mutations
 A mutagen is anything that can damage or cause
changes in DNA. This could happen when your
body forms new cells or from environmental
agents.
 When there is damage/change in an organism’s
DNA than a gene will have a mutation.
 Many ways to mutate a gene.
Mutations cont.
 When a mutation happens to cells in your body due to
certain exposure it is not passed on to offspring.
 If mutations occur in sperm or egg DNA then it is a
genetic disease that can be passed on.
 Ex. of mutations: diabetes, cancer, heart disease,
cystic fibrosis
Sex linked traits
 If a gene is found only on the X chromosome and
not on the Y chromosome, it is said to be a sex
linked trait.
 Because the gene controlling the trait is located on
the sex chromosome, sex linkage is linked to the
gender of the individual.
 The result is that females will have two copies of
the gene while males would only have one.
Sex linked traits cont.
 If the gene is recessive, then males only need one
such recessive gene to have the sex linked trait rather
than the normal two recessive genes for non sex
linked traits.
 This is why males exhibit some traits more frequently
than females.
Examples of Sex linked traits
 Red-green colorblindness
 Male Pattern baldness
 Hemophilia
 Duchenne Muscular Dystrophy
Red-green colorblindness genotypes
 Normal vision male-XCYo
 Colorblind male-XcYo
 Normal vision female-XCXC
 Normal vision female (carrier)-XCXc
 Colorblind female-XcXc
Normal Vision father X Colorblind
Mother
 Dad genotype:
 Mom genotype:
Normal vision father x normal vision mother (no
colorblindness in her family)
 Dad genotype:
 Mom genotype:
Human Genome Project
 Completed in 2003, the Human Genome
Project (HGP) was a 13-year project
coordinated by the U.S. Department of Energy
and the National Institutes of Health
Some of the project goals were:
 identify all the approximately 20,000-25,000
genes in human DNA
 determine the sequences of the 3 billion
chemical base pairs that make up human
DNA
 store this information in databases