Science Study Guide – Lesson 2 - INSIDE LIFE
Chapter 7 – TRACKING TRAITS
KEY CONCEPTS
AND
VOCABULARY
CONCEPT 1 – Traits are transmitted from parent to offspring through gametes.
Traits and Genetic Diseases of organisms are transmitted from parent to offspring
through GENES which are located in the chromosomes of reproductive Cells called GAMETES.
Gametes are special parent reproductive cells, referred to as sperm in males and eggs in
females. Genetic traits are transmitted from parent to offspring via the genes contained in
these Gamete Cells. Examples of Genetic Traits and Genetic Diseases are; natural Eye or Hair
Color, Baldness, Height, Skin Tone, Body Hair, Facial Features, and Genetic Diseases such as
Muscular Dystrophy or Downs Syndrome.
Acquired Traits, such as dyed hair color, muscles developed through exercise or a limp
resulting from an accident are NOT inherited traits and since they occur after birth, they do not
affect the genes of the organism. Therefore, Acquired traits cannot be passed along from
parent to offspring through the reproductive process. Additionally, some diseases, such as
drug addiction, alcoholism, or AIDS are transmitted via blood or other body fluids and even
though they can appear in the offspring of parents suffering from these diseases, they are not
genetic diseases because they are passed along from parent to offspring via blood or body
fluids and not via their genes.
CONCEPT 2 – Meiosis results in the formation of gametes that contain half the genetic
information of other cells.
Meiosis is the naturally occurring CELL DIVISION process that results in the creation
of reproductive cells called GAMETES. The Male Gamete is the Sperm Cell and the Female
Gamete is the Egg Cell.
Chromosomes contain the GENES that determine the traits an offspring will inherit. All
normal body cells, called Diploid Cells, contain PAIRS of Chromosomes made up of one
chromosome from each parent.
During Meiosis, the PAIRS of chromosomes contained in NORMAL DIPLOID CELLS
are divided into cells containing only ONE Chromosome from EACH PAIR. As a result of
Meiosis, the GAMETES, or the Sperm and Egg Cells, each contain only HALF of the Genetic
Information from each parent.
The Meiosis process is CRITICAL to the successful reproduction and survival of
offspring because it insures that when the Sperm and EGG combine during conception, the
offspring will have the SAME NUMBER of Chromosomes in their normal cells that each of their
parents had BEFORE MEIOSIS OCCURRED. If Meiosis did not occur, offspring would
have twice as many chromosomes in their cells and would be unable to survive.
Meiosis also insures that each parent contributes EQUAL AMOUNTS of Genetic
Information to their offspring and it creates a Gene Combination in the offspring that makes the
offspring distinct from their parents. This insures variation within the species which
promotes adaptations and survival of the species.
CONCEPT 3 – Cells contain two copies of each chromosome and therefore two copies of
each gene.
Each Chromosome, located in the nucleus of an organism cell, contains many
different Genes. Therefore, each chromosome affects many different traits. Also, each
Chromosome Pair in a normal Diploid Cell contains copies of the same genes. Therefore, each
pair of chromosomes affect the same traits.
The Meiosis process insures that each offspring receives ONE chromosome from the
FEMALE parent’s EGG and one chromosome from the MALE parent’s SPERM. Therefore,
each chromosome pair in the offspring contains 2 copies of each gene, one from the
female parent and one from the male parent.
The genes received from each parent will affect the same traits, however, the “Form” or
Allele of each gene in a pair may be different. The combined effect of the two different gene
alleles, (one from each parent), will determine how each trait is expressed in the offspring. The
combined effect of the 2 genes is referred to as the GENOTYPE and the actual observable
trait that appears in the offspring is referred to as the PHENOTYPE.
Example: If an offspring receives a gene from the female egg that is dominant for Red hair
color and a gene from the male sperm that is recessive for brown hair color, the GENOTYPE of
the offspring would be “Rr” and the resulting PHENOTYPE would be that the offspring will have
RED HAIR.
CONCEPT 4 - Variations in the traits of different generations are explained by the fact
that each individual gets two copies of each gene.
The process of Meiosis insures that each offspring receives exactly one half of its
genetic information from each parent. Each male GAMETE, or sperm cell, contains one
chromosome out of each pair of chromosomes from the original male diploid cell. Each female
GAMETE, or egg, also contains one chromosome out each pair of chromosomes from the
original female diploid cell.
During conception, the sperm cell and the egg cell unite and fuse into a single new cell
called a ZYGOTE Cell. This new cell recombines the individual chromosomes from the sperm
and egg cells and becomes a new cell containing PAIRS of chromosomes once again. This new
life, (the Zygote), contains exactly one half of its chromosomes from each parent and
therefore, it also contains exactly one half of its genetic information from each parent.
This sharing of genetic information insures that each offspring will receive some traits
from each parent. Chromosome separation during Meiosis can occur in various sequences
which can result in various Gene Alleles being present in the male and female gametes, (egg
and sperm). Additionally, CROSSOVER, another natural occurrence during the Meiosis
process can result in gene alleles actually changing from one chromosome in a pair to the
other chromosome in the same pair. These natural variations during the Meiosis process
increase the possible variations of Genotypes that can appear in offspring and increase the
variation within the species.
Mutations of genes can also occur during Meiosis which can result in defective genes, or
an imbalance of chromosome pairs in the Zygote. If mutated genes are passed along to an
offspring, they may, or may not effect the development of the offspring depending on how they
are expressed in the Genotype for that trait.
Variations in traits between offspring produced by the same parents as well as
variation in future generations is the result of Meiosis and the fact that each offspring gets
TWO copies of each gene, one from each parent. This variation insures that every
individual is unique, and distinct from all other individuals, including siblings in the same
family.
(CONCEPT 4 Continued)
Variation in a species supports adaptation to selective pressures such as
environmental changes or predatory pressures and helps insure survival against the spread of
genetic diseases or other deadly birth defects.
VOCABULARY (in alpha order)
ACQUIRED TRAITS – Characteristics that are not transmitted to an offspring via the genes of
its parents and cannot be passed along to future generations. Examples: muscles from
weightlifting, knowledge, a limp from an accident, hobbies, interests, spoken language.
ALLELES – Different forms of the same gene such as “Tall/Short”, “Green/Yellow”,
“Smooth/Wrinkled”. Forms are expressed as Letters such as “Tt for Tall/Short”, or “Gg for
Green/Yellow” with the Capitol Letter indicating the Dominant Gene and the Lower Case
Letter indicating the Recessive Gene.
ASEXUAL REPRODUCTION – See “Reproduction, Asexual”
CHROMOSOMES - Chromosomes are long, stringy aggregates of genes that carry
heredity information. They are composed of DNA and proteins and are located within the
nucleus of cells. Chromosomes determine everything from hair color and eye color to gender.
Human cells contain 23 pairs of chromosomes for a total of 46. There are 22 pairs of
Autosomes and one pair of Sex Chromosomes. Each chromosome contains a large number
of trait genes ranging from as few as 230 trait genes to as many as 2988 trait genes in a single
chromosome pair.
CLONING - The process of creating an identical copy of something. In Biology, it collectively
refers to processes used to create copies in a laboratory setting of DNA, cells, or complete new
organisms. Cloning is also very similar to the natural process of axesual reproduction. In the
Cloning process, only ONE PARENT is copied, thus, the offspring are genitacally
identical to the parent that is cloned and there is no difference in genetic information
between parent and offspring, and no variation from generation to generation.
DIPLOID CELL – A normal cell of an organism that reproduces “sexually”. These cells
CONTAIN MATCHING PAIRS of chromosomes. For each pair, one chromosome comes from
the mother’s Egg Cell and one chromosome comes from the Father’s Sperm Cell. Each pair of
chromosomes contain genes that effect the same traits of the offspring organism. However, the
alleles for each gene may be different and the traits expressed in the offspring will depend on
the Genotypes that are formed and which Alleles are dominant.
DNA – (deoxyribonucleic acid) – The molecules within a chromosome where genetic
information of an organism are stored. Genes are small sections of the DNA molecules which
are organized into distinct structures called chromosomes.
DOMINANT GENE – The form of a gene that is expressed in the offspring, even when present
with a corresponding recessive form of the same gene. Example: If the alleles for hair color are
“R” for Red Hair and “r” for Brown Hair, a genotype that contains the alleles “RR” or “Rr” would
result in an offspring with Red Hair even though the “Brown Hair allele” is present as a recessive
allele in the “Rr” genotype.
GAMETES – Special reproductive CELLS of any organism that reproduces “Sexually”. Gametes
contain only HALF of the genetic information of other “normal” body cells. In HUMANS, male
SPERM CELLS and female EGGS are GAMETES. Each of these cells contain only 23
chromosomes and are referred to as HAPLOID CELLS. This differs from normal human body
cells that contain 23 PAIRS of Chromosomes for a total of 46 Chromosomes per cell. Gametes
are produced by a special type of cell division called MEIOSIS.
GENES – Factors that determine the traits that will be present in an organism. Genes are small
sections of the DNA contained within chromosomes of an individual and are the basic units of
information passed along from generation to generation through inheritance. Each
chromosome contains a large number of trait genes ranging from as few as 230 trait genes to
as many as 2988 trait genes in a single chromosome pair.
GENETICS – The scientific field of Biology that studies genes and heredity
GENETIC TRAITS – See “TRAITS”
GENOTYPE – The expression of the ALLELES in a pair of chromosomes, such as “YY”, or Yy”
or “yy”. (See ALLELES for further clarification)
HAPLOID CELL – Special reproductive CELLS that contain only HALF THE NUMBER OF
CHROMOSOMES that other body cells contain. Gametes, which are the sperm and egg cells
in humans are examples of Haploid Cells. Each human “Egg” or “Sperm” cell contains only 23
chromosomes which represents ONE HALF of each of the 23 PAIRS of chromosomes that all
other cells in the human body contain. Gametes, or Haploid Cells are produced by a special
cell division process called MEIOSIS.
HEREDITY - The transfer of characteristics or biological traits from parent to offspring through
their genes.
HETEROZYGOUS – An organism that has TWO DIFFERENT ALLELES for a particular trait.
Heterozygous Genotypes are also referred to as “HYBRIDS”. Example: Genotype “Rr”.
HOMOZYGOUS – An organism that has TWO IDENTICAL ALLELES for a particular trait.
Homozygous Genotypes are also referred to as PUREBREEDS. Example: Genotypes “RR” or
“rr”. ***NOTE – A Genotype can be either “Homozygous Dominant” such as “RR” or
Homozygous Recessive” such as “rr” but in either case, the organism is still labeled as
being a Homozygous Genotype.
HOMOZYGOUS DOMINANT – See “NOTE” under HOMOZYGOUS for clarification
HOMOZYGOUS RECESSIVE – See “NOTE” under HOMOZYGOUS for clarification.
HYBRID – An organism with a HETEROZYGOUS Genotype, meaning it has two different
Alleles for a particular trait. Example: “Rr”. (This results from cross breeding between two
dissimilar parents)
INHERITED TRAITS – See “TRAITS”
MEIOSIS – A special type of cell division that produces GAMETES, (Egg and Sperm cells), in
male and female organisms that reproduce “sexually”. Meiosis accomplishes THREE MAJOR
TASKS: (1) it reduces the number of chromosomes in gametes to half of all the chromosomes
found in normal body cells, (2) it forms cells that will allow each parent to contribute EQUAL
AMOUNTS of genetic information to their offspring, and (3) it creates gene combinations in the
offspring that are distinct from the parents.
MEIOSIS “MATH” – Male Meiosis – 1 Normal Diploid Cell = 4 Haploid Sperm Cells
Female Meiosis – 1 Normal Diploid Cell = 1 Haploid Egg Cell
Examples – Male Cell Meiosis
1. Organism with 1 Pair of Chromosomes in a normal Diploid Cell
A. Start – 1 Diploid Cell has 1 Pair of Chromosomes, 2 total Chromosomes
B. Replication – All Chromosomes in original cell duplicate creating one cell
containing 2 Pairs of Chromosomes, 4 total Chromosomes
C. First Division – Cell divides into 2 separate cells, with EACH CELL containing
1 Pair of Chromosomes, 2 total Chromosomes, PER CELL. (4 Chromosomes total
in 2 separate cells)
D. Second Division – Each of the 2 cells from the first division divide in half creating a
total of 4 Sperm cells, (also called Gametes). Each of these sperm cells have
1 Chromosome that is the same as one of the chromosomes from the original
diploid cell. (4 Chromosomes Total in 4 separate cells)
2. Meiosis of a Human Diploid Cell
A. Start –1 Diploid Cell has 23 Pairs of Chromosomes, 46 total Chromosomes
B. Replication – All Chromosomes in original cell duplicate creating one cell
containing 46 Pairs of Chromosomes, 92 total Chromosomes
C. First Division – Cell divides into 2 separate cells, with EACH CELL containing
23 Pairs of Chromosomes, 46 total Chromosomes, PER CELL. (92 Chromosomes
total in 2 separate cells)
D. Second Division – Each of the 2 cells from the first division divide in half creating a
total of 4 Sperm cells, (also called Gametes). Each of these sperm cells have
23 Chromosomes, 1 chromosome from EACH PAIR of chromosomes that were in
the original diploid cell. (92 Chromosomes total in 4 separate cells)
MITOSIS – The process by which normal diploid cells divide, resulting in NEW CELLS that
are IDENTICAL to the original diploid cells before the division occurred. In most organisms,
Mitosis occurs continuously as normal diploid cells divide in order to replace cells that die
naturally or due to injuries or disease. Another example of Mitosis occurs following the
development of a ZYGOTE Cell as part of the conception process. After an egg and sperm fuse
to form and new diploid cell, (the Zygote), this new cell begins a series of Mitosis divisions
resulting in the formation of an embryo and the beginning of a new offspring.
PEDIGREE - A diagram or chart of a family's genealogy that shows family members'
relationships to each other and how a particular trait or disease has been inherited
PHENOTYPE – Describes the APPEARANCE OR OBSERVABLE TRAITS of an individual.
The Phenotype is primarily determined by the GENOTYPE. Example: If the alleles for hair color
are “R” for Red Hair and “r” for Brown Hair, an “RR” or “Rr” Genotype would result in
Phenotype “Red Hair” and a Genotype of “rr” would result in a Phenotype “Brown Hair”.
***NOTE – Phenotype can be impacted by environmental factors in some situations. For
example, an individual may have the “Genotype” to become TALL but a lack of proper
nutrition might prevent the normal growth pattern that is directed by the Genotype. Thus,
Phenotype can be the result of a combination of both GENES and ENVIRONMENT in
some circumstances.
PRINCIPLE OF INDEPENDENT ASSORTMENT – During Meiosis, chromosome pairs
separate “independently”. Independent Assortment occurs because genes for different traits
may be located in different chromosomes and the alignment or movement of one chromosome
during Meiosis IS NOT dependent on the movement of other chromosomes. Therefore, the
formation of Gametes contain a random assortment of genes depending on how the
chromosome pairs align and then separate during Meiosis.
PRINCIPLE OF SEGRATION – This principle states that “offspring” receive alleles from
each parent. Genes are located in chromosomes in the form of Alleles which are versions of
each Gene. Each Normal Organism Cell contains “Pairs” of Chromosomes, one from
each parent, therefore, each “pair” of Chromosomes contains one Allele or version of each
gene from each parent. During Meiosis, each “pair” of Chromosomes separate and only ONE
Chromosome FROM EACH PAIR is present in the reproductive Gamete, (the Egg or Sperm).
SEGRATION has occurred because each Gamete contains only ONE ALLELE for each
Gene Trait.
PROBABILITY – In Heredity, probability involves predicting the chances that a certain genetic
trait will develop in an offspring based on the known Genotypes of each parent for the trait being
predicted. Predicting the Genotypes of offspring is based on mathematical percentages which
may prove accurate when comparing thousands of examples. However, due to the complexity
of the reproductive process and the many variables in the Meiosis process, it would be nearly
impossible to accurately predict the probability of a specific Genotype appearing in a small
sample of offspring from one set of parents.
PUREBRED – Any organism with a HOMOZYGOUS Genotype for a particular trait. Example:
“RR” or “rr”. (Offspring reproduced from these types of organisms will continue to express this
same trait from generation to generation)
RECESSIVE GENE – The form of a gene that is only expressed when a dominate form of the
gene is not present. Example: If the alleles for hair color are “R” for Red Hair and “r” for Brown
Hair, a gene that contains the alleles “rr” will result in the offspring having Brown Hair because
there is no dominant allele present in the gene.
REPRODUCTION GENERAL - biological process by which new individual organisms are
produced. Reproduction is a fundamental feature of all known life; each individual organism
exists as the result of reproduction. The known methods of reproduction are broadly grouped
into two main types: SEXUAL and ASEXUAL.
REPRODUCTION, ASEXUAL - In asexual reproduction, an organism can reproduce without
involvement with another organism of that species. The division of a parent cell into two
daughter cells is an example of asexual reproduction. Most plants have the ability to reproduce
asexually. Asexual reproduction results in offspring with very little if any variation from
the parent cell.
REPRODUCTION, SEXUAL - Sexual reproduction requires the involvement of two individuals,
typically one of each sex. This reproduction process involves the sharing of genetic
information from each sex and insures there will be variation in the species because each
offspring receives two chromosomes and two copies of each gene, one from each parent.
Normal human reproduction is a common example of sexual reproduction.
SEXUAL REPRODUCTION – See “Reproduction, Sexual”
TRAITS – Characteristics that an organism can pass on to its offspring. Also called Inherited
Traits or Genetic Traits. Examples are: height, hair color, blood type, eye color, baldness,
genetic diseases such as Muscular Dystrophy. ***NOTE – some disorders can be passed
along from parent to offspring via blood or body fluids that are NOT Genetic Traits such
as AIDS, or Drug and Alcohol dependence.
ZYGOTE – The single cell that results from the joining of the Egg and Sperm. The Zygote will
have matching pairs of chromosomes, each pair is composed of one chromosome from the egg
and one chromosome from the sperm. The resulting Zygote will have 23 Pairs of Chromosomes
and is thus a Diploid Cell.