Cell Division and Genetics
Cell Structure and function, Cell Division, Mendelian
Genetics, Human Inheritance and Genetic Disorders
By the end of this Unit, you will be able to answer the following questions:
1. Describe the functions performed by organelles in the cell.
2. Compare and contrast bacterial, animal, and plant cells.
3. List the events that take place during the three stages of the cell cycle.
4. Identify and describe the events that occur during both mitosis and meiosis.
5. Describe the role of chromosomes in inheritance.
6. Describe Mendel’s genetics experiments and explain how geneticists use symbols to represent alleles.
7. Describe the principles of probability and how Mendel applied them to inheritance.
8. Use Punnett squares to predict the probability of traits in offspring.
9. Explain the concepts of multiple alleles, multiple genes, and sex-linked traits.
10. Describe how geneticists use pedigrees.
11. Describe the causes and symptoms of some major human genetic disorders.
Genetics and Genetic Disorders
Use your textbook to define the following terms. Include the page number where each term can be found IN the chapter. These
terms are found in Chapter 3 (Sections 1, 2, and 3) and Chapter 4 (Section 1 and 2) of the ‘Cells and Heredity’ textbook.
Term
Page
#
Definition
heredity
p. 80
The passing of traits from parents to offspring.
genetics
p. 80
The scientific study of heredity.
chromosome p. 63
A double rod of condensed chromatin; contains DNA that
carries genetic information.
genes
p. 83
A segment of DNA on a chromosome that codes for a
specific trait.
alleles
p. 83
The different forms of a gene.
p. 83
An allele whose trait always shows up in the organism
when the allele is present.
p. 83
An allele that is masked when a dominant allele is
present.
p. 81
An organism that always produces offspring with the
same form of a trait as the parent.
Hybrid
p. 84
An organism that has two different alleles for a trait; an
organism that is heterozygous for a particular trait.
probability
p. 88
The likelihood that a particular event will occur.
dominant
recessive
purebred
Term
Page #
genotype
p. 92
phenotype
p. 92
Definition
An organism’s genetic makeup, or allele combination.
An organism’s physical appearance, or visible traits.
homozygous p. 92
Having two identical alleles for a trait.
heterozygous p. 92
Having two different alleles for a trait.
Punnett
square
p. 90
codominance p. 92
Incomplete
dominance
Multiple
alleles
Sex-linked
genes
carrier
----
A chart that shows all the possible combinations of
alleles that can result from a genetic cross.
A condition in which neither of two alleles of a gene is
dominant or recessive.
A condition that occurs when one allele for a trait is not
completely dominant over the other allele. Results in a
‘blending’ of the two traits.
p. 113 Three or more forms of a gene that code for a single trait.
p. 116 A gene that is carried on the X or Y chromosome.
A person who has one recessive allele for a trait and one
p. 116 dominant allele, but does not have the trait.
Pedigree
A chart of ‘family tree’ that tracks which members of a
p. 117 family have a particular trait.
Genetic
disorder
An abnormal condition that a person inherits through
p. 119 genes or chromosomes.
Genetics – Tour of the Basics
Directions:
http://learn.genetics.utah.edu/content/begin/tour/
Complete the questions below by clicking on the tabs across the top of the website that
corresponds to each section. Listen/read the tutorial to find your answers.
What is DNA?
1. Where do the instructions that provide necessary information for a living organism reside?
In the nucleus
2. What is the name of the molecule that contains these instructions?
DNA
3. What is the shape of a DNA molecule?
Twisted ladder shape (double helix)
4. What is the 4-letter DNA alphabet?
A, C, T, G
5. How do the DNA alphabet letters pair up?
A – T and C – G
6. What are DNA “sentences” called?
genes
7. What do genes tell the cell to do?
Make proteins
8. Name each of the bases (ACGT).
A = adenine; C = cytosine; G = guanine; T = thymine
What is a gene?
1. Why are genes called the “instruction manuals” for our bodies?
They are the directions for building proteins that make our bodies function
2. What are genes made of?
DNA
3. Roughly, how many genes do we (humans) have?
25,000
4. What does “mutated” mean?
Changed instructions in a gene
5. What is the name of the disorder where a mutation causes a change in hemoglobin protein?
Sickle cell anemia
6. Genes contain instructions for building what?
proteins
What is a chromosome?
1. How long would the DNA from a single human cell be if it were stretched out? How long is this in
feet??
3 meters; 9.84 feet
2. DNA is packaged into compact units called what?
chromosomes
3. These are the steps for making a chromosome: Start with double-helix DNA ; the DNA is
wrapped around protein ; Proteins pack tightly together until formed into a chromosome .
4. How many total chromosomes does one human cell hold?
46
5. All the DNA is organized into two sets of 23 chromosomes.
6. Why do we have “sets” of chromosomes?
Get one of each from our parents
7. What are sex chromosomes and what letters are used to represent them?
Sex chromosomes determine male/female; use the letters X and Y.
8. What two letter (chromosome) combination makes males? Females?
Males = XY; Females = XX
9. How many chromosomes do mosquitoes have? Onions? Carp (fish)?
Mosquito = 6; onions = 16; carp = 104
What is a protein?
1. What is responsible for the sensation of pain?
Nerve networks
2. The nerve networks are made up of individual cells arranged end to end to transmit a pain
signal.
3. What is the job of a “receptor” protein?
They pick up pain signals and pass onto the next cell
4. What special proteins help extend nerve cells and hold them in place?
Structural protein
5. Why are structural proteins like bricks?
They stack together to form support
6. Each gene in the DNA encodes information about how to make an individual protein .
7. When a cell needs a protein, a gene is read and the information is used to make RNA (a
“molecular messenger”).
8. RNA move from the nucleus to the cytoplasm and then to the “protein making machinery”
called the ribosome .
What is heredity?
1. What is the basis of heredity? The passing of traits from parents to child
2. Our genes encode the instructions that define our traits .
3. Summarize how parents pass genes on to their child.
When parents conceive a child, they each contribute one complete set of chromosomes.
4. How many sets of chromosomes do body cells have? Sex cells?
Two sets in body cells; one set in sex cells
5. What is the name of the single cell created when sperm and egg join?
zygote
6. Why does every child inherit a unique set of chromosomes from the same parents?
Parents contribute chromosomes randomly
What is a trait?
1. What is a trait?
Notable feature/quality in a person
2. Give one example of a physical trait, a behavioral trait, and a predisposition trait.
Hair/eye color; herding instincts; heart disease
3. What two things define our traits?
Genes and the environment
4. Which trait do you have – straight thumb or hitchhikers thumb?
5. The set of genetic info for each form (of a trait) is called an allele .
6. What letter is used to represent straight thumb? Hitchhikers thumb?
Straight = H; hitchhikers thumb = h
7. Each of us has TWO alleles for thumb extension. List the possible combinations.
8. What does the word homozygous mean? Give two examples.
Two of the same allele; HH or hh
9. What does the word heterozygous mean? Give an example.
Two different alleles; Hh
10. Which allele is dominant for thumb extension? Which allele is recessive?
Straight thumb in dominant (H) and hitchhikers htumb is recessive (h)
11. A child’s traits are determined by:
Mother/father (alleles received from parents)
12. What is incomplete dominance? Give an example.
Blending of traits; example = red + white carnation gives pink carnations
13. What is the difference between “single-gene traits” and “complex traits”?
Single-gene trait = influenced by one gene; complex trait = influenced by more than one gene
Chromosomes, Genes, and alleles
(p. 100, 83)
___________________________________________________________
Dominant vs. Recessive alleles (p. 83-84) **p.12 packet**
Homozygous vs. Heterozygous (p. 92)
___________________________________________________________
Phenotype vs. Genotype (p. 92)
Codominance and Incomplete dominance (p. 92-93)
Not all alleles for traits are expressed as a dominant/recessive relationship.
B B
F F = black
feathers
RR = red flowers
R’R’ = white flowers
RR’ = pink flowers
W W
F F = white
feathers
B W
F F = BOTH black
and white
feathers
Codominance occurs when there are two variation Incomplete dominance occurs when one allele for
of a trait (two alleles), but neither one is dominant a trait is not completely dominant over the other
over the other.
allele.
As a result, BOTH alleles are expressed if
present in an individual.
As a result, there is a ‘blending’ of the
two specific traits.
Probability and Punnett squares (p. 88-90)
In a genetic cross, the allele that each
parent will pass on to its offspring is
based on probability, the likelihood that a
particular event will occur.
Mendel was the first scientist to recognize that
the principles of probability can be used to
predict the results of genetic crosses.
1. Draw a box with four (4)
quadrants.
2. Take one parent and write its
alleles ABOVE the two columns.
3. Take the other parent and write
its alleles NEXT TO the two
rows.
4. Fill in each of the boxes by
writing the letters (alleles) that
‘match up’ in that box.
Geneticists use
Punnett squares to
show all the possible
outcomes of a genetic
cross and to determine
the probability of a
particular outcome.
1. From a Punnett square, all results will be expressed as ‘…out of 4’ or ‘-/4’.
For example: 2 out of 4 OR 2/4 of the offspring above have the genotype Tt.
1 out of 4 OR 1/4 of the offspring above have the genotype tt or TT.
2. A percent can then be calculated by dividing the fraction through and X 100 to get percent
(%).
2
/4 X 100 = 50%
¼ X 100 = 25%
Multiple alleles (p. 113)
Some human traits are controlled by a single gene that has
more than two alleles.
Such a gene is said to have multiple alleles – three or more
forms of a gene that code for a single trait.
Blood type is determined by a
single gene with three alleles. This
chart shows which combinations
of alleles result in each blood
type.
A
B
I and I are codominant to each
other and both dominate over i
(recessive).
Multiple Genes (p. 114)
Multiple genes that control a trait
act together to produce a single trait
with a large number of phenotypes.
Examples: hair color, eye color, skin
color, height
Coat color in Labrador retrievers (general)
Gene #1 – Color (black or brown)
B – Black
b – brown
Gene #2 – Expression of color (yes or no)
E – expressed
e – not expressed
Coat Color
Possible Genotypes
Black
BBEE
BbEE
Yellow
BBee
Bbee
bbee
Chocolate
Sex-linked genes (p. 115-117)
The sex chromosomes carry genes that determine whether a person is male or female.
They also carry genes that determine other traits.
Females have two X chromosomes - XX
Males have one X chromosome and one Y chromosome - XY
These are homologous chromosomes and separate during meiosis
just like the other 22 pairs of homologous chromosome do!!
Some human traits occur more often in one gender than the
other.
bbEE
BBEe
BbEe
bbEe
The genes for these traits are often carried on the sex
chromosomes, most commonly on the X chromosome.
Genes on the X and Y chromosomes are often called sexlinked genes.
Because males have only one X chromosome, males are
more likely than females to have a sex linked trait that is
controlled by a recessive allele.
Females, however, tend to be carriers of a recessive sexlinked trait (they have one recessive allele for a trait and
one dominant allele)
Red-green colorblindness
C – normal vision
c – colorblind
Female:
Male:
C C
C
XX
XY
C c
c
XX
XY
c c
XX
___________________________________________________________
Genetic Disorders and Pedigrees (p. 117-118, 119-122)
A pedigree is a chart or “family tree” that tracks which
members of a family have a particular trait. (p. 118 in
textbook)
A genetic disorder is an
abnormal condition that a
person inherits through
genes or chromosomes.
Examples:
Disorder
Description
Cause
Cystic fibrosis
Body produces
abnormally thick
mucus.
Recessive allele due
to removal of three
DNA bases.
Hemophilia
Blood clots slowly or
not at all.
Recessive allele on X
chromosome.
Down’s syndrome
Mental retardation
and heart defects.
Extra copy of
chromosome 21.
Additional Information