Download Inheritance and Adaptations

Chapter 7
Lesson 1
A trait is a distinguishing characteristic of an
organism.
 During reproduction, traits are passed down from
one generation to the next, this is known as
inheritance.
 For every organism there is a range of inherited
traits.

Hair color
 Eye color
 Petal color
 Attached ear lobes

Can you name more?
 Not
all traits are inherited.
 An acquired trait is a trait that an organism
acquires or develops during his lifetime.




Loosing a limb (arm/leg)
Learning a trick/sport
Neat handwriting
Growing long hair
Can you name more?
 Organisms
pass traits to their offspring in one
of the two ways:
 Asexual reproduction – it produces offspring
who are identical to the original; passing of
traits by cell division an mitosis

Example: amoebas, bacteria, and some plants
 Sexual
reproduction – produces offspring
that are similar but not identical to the
parent or parents; requires DNA from both
reproductive cells

Example: humans, most species
DNA appears as a twisted
zipper in the nucleus;
when stretched out can
be almost 2 meters long!
It can fit into a cells
nucleus since it is tightly
coiled with proteins to
form chromosomes.
 DNA
– (Deoxyribonucleic Acid) contains genes
 Genes – a section of DNA that has genetic
information for one trait
 Genes carry instructions for traits.
Chromosomes are found in the nucleus and carry
long pieces of DNA.
 The number of chromosomes differs depending
on the species and in most species they come in
pairs.
 Humans have 23 pairs of chromosomes in each
body cell.
 Each pair contains one chromosome from the
father and one from the mother.
 Reproductive cells are known as the sperm and
egg; each contains 23 single chromosomes.
Within each chromosomes lies hundreds or
thousands of genes.





Much of this randomness
is due to meiosis.
During meiosis, new
sperm cells and egg cells
form when the
chromosomes in existing
cells replicate and
divide.
The number of
chromosomes is reduced
by half  23
chromosomes
One reproductive cell
(with replicated
chromosomes) will split
into 4 separate cells,
each containing a unique
combination of genes.
Occurs when egg cell and sperm cell combine to
form an offspring with a full set of paired
chromosomes.
 Resulting in unique offspring.
 There are many potential gene arrangements
when chromosomes combine in humans.
 A mother and father could have billions of
offspring and no two would be alike.

During reproduction an egg cell and a sperm
cells each contribute one gene for a trait.
 Each gene for a single trait is called an allele.
 Traits are expressed in the offspring by chance.

 Dominant
Allele – one whose trait shows up
in an organism when an allele is present;
represented by a capital letter
 Recessive Allele – a trait that is hidden
whenever a dominant allele is present;
represented by a lowercase letter
 Homozygous – an organism that has two
identical alleles for a trailt
 Heterozygous – an organism that has two
different alleles for a trait
… is used to
predict the
possible outcomes
of offspring.
 Genotype
– an organisms complete set of
genes; once inherited it remains
unchanged.
 An organisms environment can influence
traits expressed by the genotype.
 Phenotype – how a trait appears or
expressed
 Environmental Factors, such as physical
and social factors, are not constant and
can alter an organisms phenotype.
Light is a physical factor.
 Example: Plants need light. Plants that grow
tall in full sunlight, might not grow as tall in
low light.
 Nutrients can also affect trait expression.
 Examples:
 Low levels of nitrogen or iron in the soil may
turn a plants leaves yellow or cause them to
fall off.
 Flamingos are born white, but turn pink
because of the food they eat (algae and
crustaceans) are rich in red pigment.
 Moisture and Temperature are also physical
factors.


An organisms social group can also affect color,
body structure, or behavior.
 Examples:
 Locusts are usually solitary individuals and
are a green color. When locusts are in large
groups they apply pressure on each others
legs, causing them to change color to
yellowish-brown and swarm.
 Flamingos live in large social groups. A flock
consisting of at least 20 is needed for
breeding to occur in zoos. Adding more birds
to a flock increases breeding success. In the
wild these birds will live in flocks of 10,000.