Download 7-2.5 Summarize how genetic information is passed from parent to

The Basics of Genetics
7-2.5 Summarize how genetic information is passed from
parent to offspring by using the terms genes,
chromosomes, inherited traits, genotype, phenotype,
dominant traits, and recessive traits.
7-2.6 Use Punnett squares to predict inherited
monohybrid traits.
1. Physical characteristics (traits) are
passed or inherited from parent to
offspring through sexual reproduction.
What part of your cells contain your
genetic instructions?
• Your genetic instructions are located
in the nucleus of every cell, stored
within chromosomes.
2. Traits of an organism
are controlled by genes.
• Genes are
responsible for
the inherited
characteristics
that distinguish
one individual
from another.
2. Traits of an organism are
controlled by genes.
• A gene is a section
of a chromosome,
that determines
the inheritance of a
specific trait.
– Such as eye color
• Chromosomes are
made of tightly
wound strands of
DNA and proteins.
3. Organisms inherit genes in pairs,
one from each parent.
• Fathers pass genetic
instructions to
offspring through
sperm sex cells.
• Mothers pass genetic
instructions to
offspring through egg
sex cells.
3. Organisms inherit genes in pairs,
one from each parent.
• Each sex cell of
the parent
organism (plant or
animal) contains ½
of the genetic
material needed
to create a new
organism.
3. Organisms inherit genes in pairs,
one from each parent.
• A human body cell
contains 46
Chromosomes, which
are stored inside every
cell’s nucleus.
• Human sex cells (sperm
or egg) contain 23
chromosomes each.
Sexual Reproduction
(2 parents) creates unique offspring.
• In plants, male
chromosomes are passed
through pollen grains to
female egg cells. Once
fertilized, these eggs will
develop into seeds.
• The new plants will receive
a combination of traits
from both parents.
3. Organisms inherit genes in pairs,
one from each parent.
• One gene from the pair is
called an allele.
4. Genes may be expressed in
two different forms.
• Genotype
–Set of genes carried by the organism
–“genetic” make-up
• Phenotype
–Physical expression of the genes
–The way the trait shows
5. Some traits are dominant,
while others are recessive.
• Dominant trait will
always be expressed in
the phenotype (mask or
cover)
• Recessive trait can be
masked/covered by the
dominant trait.
• Geneticists use symbols
(letters) to represent the
different forms of a gene
(alleles)
Alleles for dominant traits are
represented by a capital letter.
Yellow seeds
are
dominant…….
Y
Alleles for a recessive trait (for the same
gene) are represented by THE SAME
lower case letter.
Green seeds are
recessive……….
y
Dominant (yellow) = Y
Recessive (green) = y
• In pea plants, tall
is dominant over
short. The letter
used to represent
the tall gene
is T.
• The short gene is
represented by t.
Tall =T
Short = t
In humans,
brown eyes are dominant over blue.
Brown = B
Blue = b
6. Dominant genes cover recessive genes when
both are inherited by an organism.
• Y + y = yellow seeds
(yellow is dominant)
• T + t = tall plant (tall
is dominant)
• B+ b = brown eyes
(brown is dominant)
A PUREBRED organism has two of the same genes for
a trait.
TT = purebred TALL
tt = purebred SHORT
A HYBRID organism has
two different alleles for a trait.
Tt = hybrid TALL
(tall is dominant.)
Bb = hybrid for black
feathers (black is
dominant.)
Will a hybrid human with the genes Bb have
brown or blue eyes?
• Bb = Brown eyes
• The dominant gene (brown),
will be expressed in a hybrid.
Why must all blue eyed people be
PUREBRED for that trait?
• If the dominant gene is present, it will
always be expressed.
• The only possible gene combination for
blue eyes is bb.
These basic laws of inheritance control the
traits of all living organisms on Earth.