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Concept 3 Genetics
Science 9
Concept 3 – Genetics
Learning Concept
 Describe, in general terms, the role and
relationship of chromosomes, genes and DNA
Concept 3 – Genetics
 There is a blueprint for each multicellular
organism found within all the cells of the body
 Known as deoxyribonucleic acid, or DNA
 Inherited material responsible for variation
Concept 3 – Genetics
 First identified in 1869
 In 1953 a scientific paper by James Watson and
Francis Crick presented the structure of DNA
 Rosalind Franklin had groundbreaking work in
discovering the shape of DNA
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Concept 3 – Genetics
 Structure is a double helix
 Resembles a ladder that has been twisted into a
spiral
 Rungs of the ladder are different in their composition



Found in pairs
Adenine (A) and Thiamine (T)
Guanine (G) and Cytosine (C)
Concept 3 – Genetics
 The arrangements of these four chemicals create a
language that cells can read
 Read in triples
 Refer to this as the genetic code – a language the
cell understands
 These chemicals are the same for all species on
Earth
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Concept 3 – Genetics
 Chromosomes are packages within the cell which
contain the DNA
 One chromosome only contains some of the
instructions for making an organism
 These are paired within a cell
 In plants and animals, chromosomes are contained
within the nucleus of the cell
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Concept 3 – Genetics
 Chromosome numbers vary from species to species
 The composition of the chromosomes also varies
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Concept 3 – Genetics
 Currently accepted in the scientific world
 Genes are responsible for inheritance of an
organism’s characteristic features
 A single gene is an uninterrupted segment of DNA,
with coded instructions
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Concept 3 – Genetics
 Genes are located on chromosomes
 Chromosomes have numerous gene locations
 Genes come in pairs
 Both genes carry instructions for the same thing
 The same genes occupy matching locations on the
chromosomes
 The DNA code may differ in each location
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Concept 3 – Genetics
 There are different forms of the genes coming
from the parents
 These different gene forms are called alleles
Concept 3 – Genetics
Learning Concept
 Distinguish between:
 Cell division that leads to identical daughter cells
 Cell division that leads to formation of sex cells
 Describe, in general terms, the synthesis of genetic
material that takes place during fertilization
Concept 3 – Genetics
 Asexual reproduction produces offspring
genetically identical to the parents
 Sexual reproduction produces offspring genetically
different from the parents
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Concept 3 – Genetics
 Binary fission occurs in unicellular organisms
 Examples: amoeba, paramecium
 Cell contents divided equally between the two new
cells
 What happens if the DNA is split between the two
cells?

How is this corrected?
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Concept 3 – Genetics
 Parent cell first makes an exact copy of its DNA
 For a short time, the parent cell has two copies of its
DNA
 When the cell divides, each new cell gets one
complete copy of the DNA
http://biodidac.bio.uottawa.ca
Concept 3 – Genetics
 A similar process occurs in multicellular organisms –
called MITOSIS
 Two new cells are produced with the same number of
chromosomes


Occurs on the body cells
Responsible for growth and cell repair in multicellular
organisms
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Concept 3 – Genetics
 Sexual reproduction requires the fusion of two
gametes
 The sperm cell
 The egg cell
 Using humans as an example,
 What happens if each gamete contained 23 pairs of
chromosomes?
 The zygote will not survive if it receives two times
the amount of DNA needed
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Concept 3 – Genetics
 MEIOSIS is a type of cell division that produces cells
with only half the DNA of a normal cell
 A sperm cell will have half the DNA
 An egg cell will have half the DNA
 When the two unite to form the zygote, it will have
a complete set of DNA
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Concept 3 – Genetics
 Meiosis involves two cell divisions to produce four
gametes
 A gamete will contain one copy of each different
chromosome
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Concept 3 – Genetics
 Textbook Activity – Who Has What Number? pg 48
 Fill in the table in your notes using the information
provided in your textbook
Organism
Cabbage
#
chromosomes
in cell after
mitosis
#
chromosomes
in a body cell
#
chromosomes
in a gamete
# of pairs of
chromosomes
18
Black Bear
38
Human
Peanut
#
chromosomes
in a zygote
23
40
Concept 3 – Genetics
 Plant and animal breeders have been conducting
experiments in selective/controlled breeding for a
long period of time
 Only organisms with desired traits were allowed to
reproduce
 Certain patterns of inheritance were eventually
detected
Concept 3 – Genetics
Learning Concept
 Identify examples of dominant and recessive
characteristics
 Recognize dominance and recessiveness provides
only a partial explanation for the variation of
characteristics in offspring
Concept 3 – Genetics
 Genetics looks at how
heritable characteristics
are passed from one
generation to the next
 Work was began by
Gregor Mendel, an
Austrian monk
 Traced patterns of
inheritance in pea plants

Discovered fundamental
principles that led to
modern genetics
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Concept 3 – Genetics
 A purebred organism (plant or animal) is one whose
ancestors ALL had the same form of a trait
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Concept 3 – Genetics
 A hybrid organism (plant or animal) is one who was
produced from two purebreds with a different
form of the trait
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Concept 3 – Genetics
 Dominant traits are those which are typically
always expressed/observed if ONE is present
 Two dominant alleles are inherited
 Example



Female provided allele for Yellow seed (dominant)
Male provided allele for Yellow seed (dominant)
Offspring will inherit both alleles
 Two dominant alleles are inherited and yellow seeds will be
observed
Concept 3 – Genetics
 Two opposite-acting alleles are inherited
 Example



Female provided allele for Tall plants (dominant)
Male provided allele for Dwarf plants (recessive)
Offspring will inherit both alleles
 Tall is a dominant alleles, so while both alleles are
inherited, a TALL plant will be observed
Concept 3 – Genetics
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Concept 3 – Genetics
 Recessive traits are those which are ONLY
expressed/observed when TWO are present
 Two recessive alleles are inherited
 Example:



Female provided allele for white flowers
Male provided allele for white flowers
Offspring will inherit both alleles
 Two recessive alleles are inherited and a white flower will
be observed
Concept 3 – Genetics
 Which of the examples listed in these notes (seed
color, tall/dwarf plants, flower color) represents
 A hybrid?
 A purebred?
Concept 3 – Genetics
Learning Concept
 Investigate the transmission of characteristics from
parents to offspring, and identify examples of
characteristics in offspring that are:
 The same as the characteristics of both parents
 The same as the characteristics of one parent
 Intermediate between parent characteristics
 Different from both parents
Concept 3 – Genetics
 Recall that each adult has a pair of chromosomes,
and alleles are gene variations carried on those
chromosomes
 There is written “code” for genetics to show
dominant versus recessive traits
 We call the written “code” the organism’s genotype
Concept 3 – Genetics
 Dominant traits are always written as the capital
letter
 Recessive traits are always written as the lower
case of the same letter
 For yellow seeds


Dominant trait for yellow could be Y
Recessive trait for green will then be y
Concept 3 – Genetics
 A pea plant with the yellow seed color will have
two alleles
 Dominant traits are expressed when:


Two dominant alleles are inherited
Two opposite-acting alleles are inherited
 What are the two possible genotypes for this pea
plant?
Concept 3 – Genetics
 A pea plant with the green seed color will also have
two alleles
 Recessive traits are expressed when:

Two recessive alleles are inherited
 What are the one possible genotypes for this pea
plant?
Concept 3 – Genetics
 Science Log
 Why is it possible for two plants that express the
dominant yellow seed color to have one green seed
offspring?
Concept 3 – Genetics
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Concept 3 – Genetics
 Give it a try ...
 Page 52 – Exploring Genetic Possibilities
Concept 3 – Genetics
 Other patterns of inheritance also exist, due to
 Incomplete dominance
 Complex patterns of inheritance
 Environmental factors
Concept 3 – Genetics
 Incomplete dominance arises when traits are not
truly dominant or recessive
 A purebred red snapdragon, when crossed with a
purebred white snapdragon, will produce all pink
offspring



What is the genotype of the red snapdragon?
What is the genotype of the white snapdragon?
What is the genotype of the pink snapdragon?
Concept 3 – Genetics
 Environmental factors can cause variations in
things such as height, weight, etc.
 Presence of environmental factors can influence the
genes


Consumption of alcohol during a pregnancy will interfere
with normal development of brain structures and facial
features
Medication can cause structural deformities
 Example: thalidomide in the late 1950s
Concept 3 – Genetics
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