Genetics & Heredity
Cells & Microscopes
Genes are units of information
that are inherited from parent to
Offspring get half their genes
from each parent - 23 chromosomes from mom and 23 chromosomes from dad. This unique
combination of genes is what
makes each person different.
Mendel discovered the basic rules
of inheritance - that traits are
A microscopes is a tool with 1 or
more lenses which magnifies an
object and makes it appear larger.
scientists to discover CELLS
- the smallest unit of life.
Total magnification =
Eyepiece Lens x Objective Lens
always carry with 2 hands
Begin viewing with the low
Basic microscope rules:
It allows us to
power objective (shortest).
see objects that Start focusing using the
are much too
coarse adjustment knob
small to see
(big one), then use the
with the unaidfine adjustment knob to
ed eye. The
sharpen the focus.
invention of the
DON’T use the coarse admicroscope was
justment knob with the
high power objective
science be(longest lens). You can
cause it allowed
crack the lens & slide!
All living things are made of
cells. In the center of a cell is
a NUCLEUS, which is im-
portant because it is the
“brain” or control center of
the cell. It directs everything
the cell does and contains
controlled by PAIRS of factors
(alleles); and that dominant alleles
can hide recessive alleles.
Punnett Squares are a way to
show all the possible outcomes of
a genetic cross and determine the
probability that an offspring will
have a phenotype & genotype.
Pedigrees are used to track inherited traits through several genera-
DNA, Chromosomes, and Genes
All genetic material is found
inside the nucleus of a cell.
Your GENES are recipes for
making proteins — and since
you are made of proteins —
your genes are the recipe for
Each human cell has 23 pairs
of chromosomes (46 in all!).
tions of a family and can be used
DNA - is short for the chemical
name: Deoxyribonucleic Acid.
DNA is shaped like a twisted
ladder called a double helix. It
has 2 long strands (sugarphosphate backbone) that are
connected by millions of base
pairs. These are combinations
of 4 different chemicals
(nitrogen bases). The nitrogen
bases pair in a certain way:
Cytosine pairs with Guanine
to understand genetic diseases.
Adenine pairs with Thymine
The ORDER of these base pairs
is the recipe for making proteins and is your genetic code.
Check the textbook for
Chromosomes—are made of
tightly wound up DNA.
Genes—are recipes for proteins and are made of long
sections of DNA located on a
specific part of a chromosome.
DNA - is your genetic code.
Everyone’s genetic code is
unique & different. Each person
gets different combinations of
genes from both parents.
DNA replication - is how
DNA creates a
copy of itself.
It unzips into 2
are used as
create 2 new
Protein Synthesis - is how
DNA makes protein. A copy of
DNA called mRNA is made in
the nucleus. It then travels
out in the cell to a ribosome
where proteins are made by
joining together long chains of
Mutations - are mistakes
that sometimes happen when
DNA is copied. Mutations can
happen if a section of DNA is
deleted, added or substituted.
Mutations can be HARMFUL,
HELFPUL or they may make
NO DIFFERENCE AT ALL.
GENETICS & HEREDITY UNIT REVIEW
Gregor Mendel’s Experiments
GREGOR MENDEL - was an Austrian
monk who lived in the 1800s and conducted thousands of experiments on
pea plants. He is known as the “father
of genetics” for figuring out the basic
rules of how traits are passed from parents to offspring.
The short trait was “lost” (because “t”
was recessive, and the tall allele “T” was
dominant). When he crossed the two
hybrid tall plants (Tt), the short trait (tt)
reappeared 25% of the time.
Phenotype - an organism’s physical
appearance (how does the trait look?
Example: Tall stem or Short stem)
For example, he crossed a purebred tall
plant (TT) with a purebred short plant
(tt) and all the offspring were TALL(Tt).
Genotype - an organism’s genetic
make-up. (Which alleles does it have?
Example: TT or Tt or tt)
Allele - one form of a gene. Each gene
is controlled by 2 alleles.
Dominant allele - it is more “powerful”
and can mask/hide a recessive allele.
Example: “Tall” stems are controlled by
the dominant allele (shown with a capital “T”).
Recessive allele - it is one that is hidden when the dominant allele is present.
Example: “Short” stems are controlled
by the recessive allele (shown with a
Homozygous (Purebred) - when both
alleles for a gene are the same (TT or
Heterozygous (Hybrid) - when there
are 2 different alleles for a gene.
Probability & Punnett Squares
A Punnett Square - is a tool you can
use to figure out all the possible offspring from a genetic cross.
If you know the genotypes of both the
parents, a punnett square can tell you
the probability (% chance) that 2 parents will have an offspring with a certain phenotype & genotype.
Example: If you cross 2 heterozygous
(hybrid) plants with ROUND seeds,
what are the possible phenotypes and
genotypes of the offspring?
(“R” for round seeds is dominant over
“r” for wrinkled seeds).
1) Begin by placing
the genotype of
one parent along
the top of the
square and the
genotype of the
along the side.
2) Then copy one
to the right,
across each pair
of boxes in the
3) Next copy the other
parent’s alleles down,
into each pair of boxes
in the square below.
4) The completed square
shows that 3/4 (75%) of the possible
offspring will have ROUND seeds and 1/4
(25%) will have wrinkled seeds. 1/4 will
be homozygous dominant (RR), 2/4 will be
heterozygous (Rr), and
1/4 will be homozygous
Some human traits are controlled by
single genes (with 2 or more alleles)for example, widow’s peak, tonguerolling, hitchhiker’s thumb, blood type.
Other human traits are controlled by
multiple genes which act together as
a group to produce a single trait—for
example, height and skin color have
many different phenotypes because
they are influenced by many genes.
Human traits are influenced by
genes AND environment.
One of the 23 pair of human chromosomes are called sex chromosomes because they determine gender— two X chromosomes result in a
female (XX), one X and one Y
chromosome results in a male (XY).
Genetic disorders are caused by mutations
in the DNA of genes or chromosomes - Cystic
Fibrosis, Sickle Cell Disease, and Down Syndrome are examples.
Some of these diseases are recessive, so it’s possible for a person to be a carrier—they carry 1 copy of
the mutated gene, but they don’t have the disease,
because they have a copy of the dominant normal
gene which keeps them healthy. (Sickle cell is recessive— you need 2 copies of the gene to be sick.