N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
Heredity
Spring 2006
HEREDITY
In this 7th grade unit the student knows that species can change through
generations and that the instructions for traits are contained in the genetic
material of the organisms. The 7th grade student is expected to identify that
sexual reproduction results in more diverse offspring and asexual reproduction
results in more uniform offspring. The 7th grade student will also compare traits of
organisms of different species that enhance their survival and reproduction and be
able to distinguish between dominant and recessive traits, recognizing that
inherited traits of an individual are contained in genetic material.
The 7th grade student should come with an understanding of how adaptive
characteristics help individuals survive and reproduce. They should already be able
to identify some inherited (vs. learned) traits of plants and animals. The 4th grade
student first examined adaptations and how they affect survival. They also
determined the difference between inherited and learned traits. In the 5th grade,
the student revisits the effect of adaptations on survival and identifies traits that
are inherited from parent to offspring. In the 6th grade, the concept of
inheritance is expanded to include changes in traits that can occur over several
generations and the study of cells, including identification of the nucleus as the
structure that contains genetic material (DNA).
Sexual and Asexual Reproduction
In sexual reproduction, two parents produce offspring that share the
characteristics of both parents. In asexual reproduction, a single parent produces
offspring that are exactly the same as the parent. Organisms that reproduce
sexually have an advantage over organisms that reproduce asexually. The offspring
from two parents that have reproduced sexually are more diverse than when
offspring are produced asexually. Sexual reproduction allows variation within the
species. The fact that variation helps organisms survive in a changing environment
is a very important concept for students to understand and take away from this
unit. In sexual reproduction, one parent produces an egg while the other parent
produces a sperm. The egg and sperm each have half of the numbers of
chromosomes that is contributed to the new offspring. Even in plants, sexual
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
Heredity
Spring 2006
reproduction can be found. One part of the plant may produce pollen (which is the
male part) and another part of the plant may produce the fruit (which has seeds
and is considered the female part). Examples of asexual reproduction would be
shoots, runners, cuttings, and buds. Unless a mutation occurs, the offspring that is
a product of asexual reproduction will be identical to the parent organism because
the chromosomes being inherited are simply copies of what the parent has.
Students at this level do not need to know the processes of mitosis and meiosis.
These processes will be introduced in high school biology.
Traits and Genetic Material
Gregor Mendel, an Austrian monk who lived in the 1800’s, is known as the father of
genetics. Genetics is the study of heredity. Even though Gregor Mendel did not
know about chromosomes and DNA (discovered in 1953), he was still able to
mathematically figure out which trait was dominant and which trait was recessive.
He chose the garden pea for his studies. During experiments in which he mated
the plants, he began to notice patterns of inheritance which enabled him to predict
the probability of a particular trait be inherited. As a result, he proposed the
concept of dominant and recessive genes. His ideas were based on careful
observation, record-keeping, and mathematics.
Dominant and Recessive Traits
Genes are segments of DNA that give instructions to the cell for expressing traits.
In sexual reproduction, each parent contributes one set of genes to the offspring.
The offspring gets two forms of the same trait for every characteristic, one from
each parent. The different forms of a gene are called alleles. The combination of
alleles an organism inherits from its parents is the genotype. An organism’s
appearance that occurs as a result of the alleles is its phenotype. When two
different alleles for a trait occur together, the dominant trait will be expressed.
The one that is not expressed when the dominant form of trait is present is
considered to be recessive. A expression of a recessive gene is “hidden” by the
dominant one.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
Heredity
Spring 2006
Alleles are represented with capital and lowercase letters. The letter of the
alphabet chosen should match the dominant trait. The dominant trait should also
be the one written with a capital letter. For example, an allele for pea pod shape
would be S because smooth is dominant. The recessive characteristic is bumpy and
would be referred to with a lowercase s. When two different alleles occur
together, such as Ss, the dominant allele will be expressed, resulting in a smooth
phenotype.
This is a student’s first introduction to dominant and recessive traits. In the
example given above, the student should be able to recognize which genotypes lead
to a dominant expression in the phenotype and how the recessive genotype is the
only one that will lead to a recessive expression in the phenotype. For example,
students should know that SS and Ss plants would both be smooth and only ss
plants would be bumpy. Students are never expected to know which trait is
dominant over another. This information must always be provided by the teacher.
The 8th grade student will expand on this information through the use of punnett
squares to make predictions about possible outcomes of genetic combinations.
The following chart contains some examples of traits in humans that are controlled
by a single pair of alleles:
DOMINANT TRAITS
RECESSIVE TRAITS
unattached earlobes
attached earlobes
straight thumb
hitchhiker’s thumb
Source: http://extension.usu.edu/aitc/teachers/pdf/heredity/comparing_traits.pdf
can roll tongue
Source: http://extension.usu.edu/aitc/teachers/pdf/heredity/comparing_traits.pdf
cannot roll tongue
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
DOMINANT TRAITS
freckles
Source: http://extension.usu.edu/aitc/teachers/pdf/heredity/comparing_traits.pdf
Heredity
Spring 2006
RECESSIVE TRAITS
no freckles
Source: http://extension.usu.edu/aitc/teachers/pdf/heredity/comparing_traits.pdf
naturally rests left thumb on top when
hands are folded
dimples
naturally rests right thumb on top when
hands are folded
middigital hair
no middigital hair
widow’s peak
no widow’s peak
no dimples
Natural Selection
Students have studied adaptations since the 4th grade. This is the first time,
however, that natural selection will be discussed. Natural selection is a process by
which organisms with certain traits survive and reproduce at a higher rate than
organisms without these traits. Natural selection explains how a population can
change over time and why some traits are more beneficial than others.
Environments also change, and sometimes they change too quickly. When this
happens, the organisms will either die out or the few with the right adaptations will
survive and pass their traits on to their offspring. The theory of natural selection
has four main points: overproduction, genetic variation, struggle to survive, and
successful reproduction.

overproduction: In an effort to allow a population to survive most organisms
will produce more offspring than is needed. In general, the more parental
care needed, the fewer the offspring. In some cases, more offspring are
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
Heredity
Spring 2006
produced to increase the odds of survival for species that are not well
protected by parents.

genetic variation: Among the many individuals of a single population of
species there exists variation or different forms of a trait. Some forms of
the trait may be more advantageous than others, depending on the
environment.

struggle to survive: All species compete for food, water, air, and habitat (a
place to live). Those species that have the adaptations best suited to the
environment are the ones most likely to survive.

successful reproduction: Individuals do not have to reproduce in order to
survive, however, some individuals in a population have to reproduce or the
species will die out. The organisms that are best adapted are going to be
the ones who reproduce and this allows the species to continue its survival in
nature.
The 7th grade student needs to know that some traits enhance survival and as a
result, lead to greater chances of reproducing and continuing the species. The
following pictures and chart provide some examples of adaptations:
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
5
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 5
Heredity
Spring 2006
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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