Cell Division
Introduction
Just like a butterfly passes through different phases (such as caterpillar, chrysalis, and adult butterfly)
there are a series of phases in a cell's life as it gets ready to divide. The sequence of phases leading up to cell
division, ending with cell division itself, is called the cell cycle. Each new cell must be identical to the original
with a complete copy of the organism’s DNA. The process of cell division in eukaryotic cells is carefully
controlled because it allows organisms to grow, repair injuries, and reproduce. If the cell cycle is not carefully
controlled, it can cause a disease called cancer in which the cells divide out of control. A tumor can result from
this kind of growth.
Chromatin, Chromosomes, and Chromatids, Oh My!
Throughout the cell cycle, DNA takes on different shapes and each of those shapes has another name.
In the beginning of the cell cycle, the DNA looks like a pile of string, which is called chromatin. At the
beginning of the cell cycle, the chromatin is copied, so that the new cell will have an identical copy of the
original DNA. Before the nucleus divides, the DNA in the nucleus wraps around proteins to form
chromosomes, which look like worms and arrange themselves into an “X” shape. Each half of the “X” is
identical to the other and are called sister chromatids. Each organism has a unique number of chromosomes.
In human cells, our DNA is divided up into 23 pairs of chromatids, or 46 chromosomes.
The Cell Cycle
Like a human life cycle, which is made up of
different phases (childhood, adolescence,
adulthood) the cell cycle also occurs in a series of
phases. These steps can be divided into three main
components: interphase, mitosis, and cytokinesis.
Interphase is the stage when the cell mostly
performs its “everyday” functions. For example, it is
when a kidney cell does what a kidney cell is
supposed to do. The cell also gets ready to divide
during this time. The nucleus divides during mitosis,
and then the cell splits in half during cytokinesis. A
summary of all of the phases is pictured to the right.
Interphase
Most of the cell cycle consists of interphase, the time between cell divisions. Interphase can be divided
into three stages:
1. The first growth phase (G1): During the G1 stage, the cell doubles in size and doubles the number of
organelles.
2. The synthesis phase (S): The DNA is replicated during this phase. In other words, an identical copy of
the cell’s DNA is made. This ensures that each new cell has a set of genetic material identical to that of
the parental cell.
3. The second growth phase (G2): Proteins are synthesized that will help the cell divide. At the end of
interphase, the cell is ready to enter mitosis.
Mitosis
During mitosis, the nucleus divides. One nucleus becomes two nuclei, each with an identical set of DNA.
Mitosis consists of four separate phases:
1. Prophase: The DNA coils into chromosomes, the membrane around the nucleus begins to disappear,
cylindrical organelles (called centrioles) move to opposite ends of the cell, and thread-like structures
(called spindle fibers) sprout from the centrioles.
2. Metaphase: The nuclear membrane has disappeared completely, the chromosomes line up in the
middle of the cell, and spindle fibers attach to the chromosomes at the center (an area called the
centromere).
3. Anaphase: The spindle fibers pull the chromosomes apart at the centromere and pull them to opposite
ends of the cell.
4. Telophase: A nuclear membrane forms around each group of chromatids, the chromatids unwind, and
cytokinesis begins.
Cytokinesis
Mitosis is followed by
cytokinesis, when the cytoplasm
divides, resulting in two cells. After
cytokinesis, cell division is
complete. The one parent cell (the
dividing cell) forms two genetically
identical daughter cells (the cells
that divide from the parent cell).
The term "genetically identical"
means that each cell has an
identical set of DNA, and this DNA
is also identical to that of the
parent cell.
Review of “Cell Division” Reading
1. What do chromatin, chromosomes, and chromatids have in common? How are they different?
2. What are the three parts of the cell cycle?
3. What happens during mitosis?
4. What are the four phases of mitosis, in the correct order?
5. What is cytokinesis, and when does it occur?
Cell Division Notes
The cell cycle is the process by which cells replicate and divide. There are three parts: interphase
(preparation), mitosis (nuclear division), and cytokinesis (splitting).
Why do cells divide?
How do cells know how to divide?
1.
2.
The ________ has the ____________________ for
3.
all the cell’s activities.
How long does it take in embryonic (offspring) cells?
How long does it take for body cells (adult human)?
1. Interphase – “COPYING”
 Cell ____________________ in size.
 ________ (looks like a pile of string) replicates.
 ______________________ double in number.
2. Prophase – “PAIRING”
 DNA ____________ into chromosomes, which pair with their copy
 Centrioles move toward __________________ poles.
 Spindle fibers __________.
 Nuclear membrane begins to __________________.
3. Metaphase – “MIDDLE”
 Nucleus has ____________________ completely.
 Chromosomes line up in the _______________ of the cell.
 Spindle fibers ______________ to centromeres.
4. Anaphase – “APART”
 Centromeres __________________.
 Chromatids ________________ and move toward opposite poles.
5. Telophase – “TWO”
 Nuclear membrane _____________ around each group of chromosomes.
 Chromosomes _____________.
 Cytokinesis ____________.
6. Cytokinesis – “CYTOPLASM SPLITS”
 Cytoplasm ______________.
 ________ cell becomes _________ cells.
Cell Cycle Labeling
91
Formative Assessment: Cell Division
DIRECTIONS: Match each phase with its “theme.”
_____ 1. Interphase
A. Apart
_____ 2. Prophase
B. Copying
DIDIRECTIONS: Match each term with its definition.
_____ 7. Centriole
A. Half an “X” shape.
_____ 8. Centromere
B. The “X” shapes.
_____ 9. Chromatid
C. Cylindrical organelle.
_____ 3. Metaphase
C. Cytoplasm Splits
_____ 4. Anaphase
D. Middle
_____ 5. Telophase
E. Pairing
_____ 10. Chromosome
D. Thread-like structures.
_____ 6. Cytokinesis
F. Two
_____ 11. Spindle Fibers
E. Center of the “X.”
DIRECTIONS: Number the pictures to show the correct order of the phases of cell division.
Lab: Cell Division
Objectives:

Use models to study cell division.

Learn that cell division is the process by which cells pass on their genetic information.
What will happen to the number of chromosomes during cell division?
Hypothesis:
If a cell goes through cell division, then the number of chromosomes will ______________________________
__________________________________________________________________________________________
.
Warm-Up Questions:
1. Why do cells divide?
______________________________________________________________________.
2. During cell division, one cell becomes ________.
3. How many chromosomes do humans have? ________.
4. How does the DNA of a daughter cell compare to the parent cell? _________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Data Table:
Drawing
Before
Interphase
End of
Interphase/
Beginning of
Prophase
End of
Prophase/
Beginning of
Metaphase
End of
Metaphase/
Beginning of
Anaphase
End of
Anaphase/
Beginning of
Telophase
End of
Telophase/
Beginning of
Cytokinesis
End of
Cytokinesis/Be
ginning of
Interphase
Number
of Cells
# of Nuclei
(per cell)
# of
Chromatids
(per cell)
Cell
Membrane
Present?
Nuclear
Membrane
Present?
Formative Assessment #2: Cell Division
DIRECTIONS: Match the event(s) to the phase in which they happen.
_____ 1. Anaphase
A. Everything in the cell doubles.
_____ 2. Cytokinesis
B. The cytoplasm splits.
_____ 3. Interphase
C. Nuclear membranes form around each set of chromosomes, which unwind.
_____ 4. Metaphase
D. Centromeres divide and chromatids move to opposite ends.
_____ 5. Prophase
E. Chromosomes line up in the middle of the cell.
_____ 6. Telophase
F. DNA coils into chromosomes and nuclear membrane begins to disappear.
DIRECTIONS: Match each term with its definition.
_____ 7. Centriole
F. Centers of chromosomes.
_____ 8. Centromere
G. Thread-like structures that attach to centromeres.
_____ 9. Chromatid
H. Cylindrical organelle that sprouts spindle fibers.
_____ 10. Chromosome
I. Half of a chromosome.
_____ 11. Spindle Fibers
J. Coiled structures of DNA.
DIRECTIONS: Number the pictures to show the correct order of the phases of cell division.
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____ 1. Which event occurs during interphase?
a. The cell carries out metabolic growth processes.
b. Centrioles appear.
c. Spindle fibers begin to form.
d. Centromeres divide.
____ 2. During which phase of mitosis do the chromosomes line up along the middle of
the dividing cell?
a. prophase
b. telophase
c. metaphase
d. anaphase
____ 3. The process of the cell cycle in which a cell divides into two daughter cells is
called
a. cytokinesis.
b. metaphase.
c. interphase.
d. mitosis.
____ 4. The cell cycle is the
a. series of events that cells go through from “birth” to
reproduction.
b. period of time between the birth and the death of a cell.
c. time from prophase until cytokinesis.
d. time it takes for one cell to undergo mitosis.
Figure 9-1
____ 5. The region labeled B in Figure 9-1 is called the
a. centromere.
b. centriole.
c. sister chromatids.
d. spindle microtubules.
____ 6. During which phase(s) of mitosis are structures like the one shown in Figure 91 visible?
a. anaphase and prophase
b. prophase and metaphase
c. metaphase only
d. anaphase and interphase
____ 7. Which of the following is a correct statement about the events of the cell cycle?
a. Little happens during the G1 and G2 phases.
b. DNA replicates during cytokinesis.
c. The Mitotic phase is usually the longest phase.
d. Interphase consists of the G1, S, and, G2 phases.
____ 8. Unlike mitosis, meiosis results in the formation of
a. diploid cells.
b. haploid cells.
c. 2n daughter cells.
d. body cells.
____ 9. Crossing-over rarely occurs in mitosis, unlike meiosis. Which of the following is
the likely reason?
a. Chromatids are not involved in mitosis.
b. Tetrads rarely form during mitosis.
c. A cell undergoing meiosis does not have homologous
chromosomes.
d. There is no prophase during mitosis.
____10. Which of the following is NOT a correct statement about the events of the cell
cycle?
a. Interphase is usually the longest phase.
b. DNA replicates during the S phase.
c. Cell division ends with cytokinesis.
d. The cell grows during the Mitotic phase.
____11. Which of the following is a phase in the cell cycle?
a. G1 phase
b. G2 phase
c. Mitotic phase
d. all of the above
____12. The mitosis is …
a. series of events that cells go through from “birth” to
reproduction.
b. period of time between the birth and the death of a cell.
c. time from prophase until the S-phase of the cell.
d. time from prophase to telophase of the nucleus.
____13. The two main processes of the divisional mitotic phase are called
a. mitosis and interphase.
b. telophase and cytokinesis.
c. the M phase and the S phase.
d. mitosis and cytokinesis.
____14. Which of the following is a phase of mitosis?
a. cytokinesis
b. interphase
c. prophase
d. S phase
____15. Unlike mitosis, the end of meiosis usually results in the formation of
a. two genetically identical cells.
b. four genetically unique cells.
c. four genetically identical cells.
d. two genetically unique cells.
____16. What is shown in Figure 9-2?
a. independent assortment
b. anaphase I of meiosis
c. crossing over
d. replication
Figure 9-2
USING SCIENCE SKILLS
Figure 9-4
17. Observing: List the correct order for the diagrams of the mitosis process in
Figure 9-4.
a. A, B, C, D
b. D, C, B, A
c. D, A, C, B
d. D, B, A, C
18. Inferring: What would be the (diploid) chromosome number of the cell shown
in Figure 9-4?
a. 4
b. 8
c. 2
d. 16
19. Inferring: Identify the structure labeled Y in Figure 9-4.
a. nucleus
b. centrosome
c. spindle microtubule d. sister chromatids
20. Observing: What phase is shown in diagram C of Figure 9-4?
a. prophase
b. metaphase
c. anaphase
d. telophase
Figure 9-6
21. Interpreting Graphics: In Figure 9-6, what is the entire structure labeled X in
phase A?
a. Chromatin
b. Tetrad
c. A chromosome
d. Sister chromatids
22. Observing: In Figure 9-6, during which phase would crossing-over and genetic
recombination occur?
a. D
b. A
c. G
d. E
23. Identifying: In Figure 9-6, identify the phase of meiosis for letter F.
a. Anaphase I
b. Telophase/Cytokinesis II c. Metaphase I
d. Anaphase II
Interpreting Graphics: Use the meiosis diagrams below to identify the most
appropriate answers.
24. Identify the process:
a. Prophase I
b. Prophase II
c. Metaphase I
d. Metaphase II
25. Identify the genetic material:
a. Chromatin
b. Sister-chromatids
c. A chromosome
d. Tetrads of homologous
chromosomes
27. Identify the process:
a. Prophase II
b. Anaphase I
c. Telophase/Cytokinesis I
d. Telophase/Cytokinesis II
28. Identify the genetic material:
a. Chromatin
b. Sister-chromatids
c. Homologous chromosomes
d. Tetrads of homologous
chromosomes
30. Identify the process:
a. Telophase/Cytokinesis I
b. Anaphase II
c. Telophase/Cytokinesis II
d. Metaphase I
31. Identify the genetic material:
a. Chroma
b. Sister-chromatids
c. Chromosomes
d. Tetrads of homologous
chromosomes
WLHS/Biology
Name: __________________
THE CELL CYCLE WORKSHEET
.
Fill in the blank: Some will be used more than once.
A. Prophase
B. Interphase
C. Telophase
D. Metaphase
E. Anaphase
F. Centromere
G. Chromatid
H. Cytokinesis
I. Mitosis
J. Spindle fiber
K. Cell plate
______________1. During what phase of mitosis do centromeres divide and the chromosomes move toward
their respective poles?
______________2. What is the phase where chromatin condenses to form chromosomes?
______________3. What is the name of the structure that connects the two chromatids?
______________4. In a chromosome pair connected by a centromere, what is each individual chromosome
called?
______________5. What are the two parts of cell division?
______________6. What structure forms in prophase along which the chromosomes move?
______________7. Which phase of mitosis is the last phase that chromatids are together?
______________8. Which phase of the cell cycle is characterized by a non-dividing cell?
______________9. What structure is produced when protein fibers radiate from centrioles?
______________10. What forms across the center of a plant cell near the end of telophase?
______________11. The period of cell growth and development between mitotic divisions?
The diagram below shows six cells in various phases of the cell cycle. Note the cells are not arranged
in the order in which the cell cycle occurs. Use the diagram to answer questions 1-7.
1. Cells A & F show an early and a late stage of the same phase of the cell cycle. What phase is it?
2. Which cell is in metaphase?
3.
Which cell(s) is in the first phase of Mitosis?
4.
In cell A, what structure is labeled X?
5.
List the diagrams in order from first to last in the cell cycle.
6. What is the longest phase of the cell cycle?
7. a. Are the cells depicted plant or animal cells? Explain your answer.
b. If it were the other type of cell what would be different in the diagrams?
8. Why is mitosis important?
9. Predict what would happen if an individual had faulty spindle fibers.
10. Predict what would happen if cytokinesis was skipped.
In the picture, identity the following
stages in the cell cycle.
A
D
A. __________________
B. __________________
B
C. __________________
C
D. __________________
E. __________________
Which phase is not represented in this picture? Why?
E
Cell Cycle and Division
Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true.
____
1. The two main phases of the cell cycle are the cytokinetic phase and interphase.
____
2. The phase in which a cell spends most of its life is interphase.
____
3. During the mitotic phase, the nucleus divides.
____
4. Some cells stop the cell cycle in the interphase G1 stage.
____
5. A unicellular organism called a prokaryote does not have a membrane-bound nucleus.
____
6. The period of growth and development in the cell cycle is called interphase.
____
7. The process by which cells duplicates takes the same amount of time no matter which type of cells are
duplicating.
____
8. The cell cycle results in two different cells being created.
Multiple Choice
Identify the choice that best completes the statement or answers the question. Write the letter of your choice on the blank
line.
____
____
____
____
____
____
____
1. Animal cells do NOT have ____.
a. centrioles
c. cell plates/walls
b. centromeres
d. cytoplasm
2. Most of the life of any cell is spent in a period of growth called ____.
a. telophase
c. interphase
b. prophase
d. anaphase
3. Which choice is NOT a process of the cell cycle?
a. death
c. development
b. division
d. growth
4. Which choice best describes the cell cycle?
a. Cells grow and develop during interphase. Cells reproduce during the mitotic phase.
b. Cells grow and develop during the mitotic phase. Cells reproduce during interphase.
c. The nucleus of a cell divides during interphase. The cytoplasm of a cell divides during the
mitotic phase.
d. The nucleus of a cell divides during the mitotic phase. The cytoplasm of a cell divides
interphase.
5. How long does it take for most dividing human cells to complete a cell cycle?
a. a few minutes
c. a year
b. a day
d. about 7 years
6. What is the first thing that happens when a new cell is produced?
a. It gets smaller.
c. It divides again.
b. It gets larger.
d. It rests.
7. During which stage of interphase do cells perform their normal cell functions (such as growing and making
enzymes to digest your food)?
a. S stage
c. G2 stage
____
8.
____
9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
____ 15.
____ 16.
____ 17.
b. G1 stage
d. Mitosis
During which stage of interphase do cells copy their DNA?
a. S stage
c. G2 stage
b. G1 stage
d. Cytokinesis
During which stage of interphase do cells store energy in final preparation for use in the mitotic phase?
a. G2
c. S
b. G3
d. S2
During the S stage of interphase, pairs of identical chromosomes are held together by which structure?
a. centromere
c. connectroid
b. chromatid
d. centromatid
Identify two stages of the mitotic phase.
a. prophase and metaphase
b. cytokinesis and interphase
c. mitosis and interphase
d. interphase and metaphase
If a cell has 22 duplicated chromosomes, how many chromatids does it have?
a. 22
c. 11
b. 44
d. 88
What is the shortest phase of interphase?
a. G2
c. S
b. metaphase
d. prophase
Which type of cell divides by the cell membrane pinching together until the two cells split apart?
a. plant
c. cytoplastic
b. animal
d. chromosomal
Which best describes how a plant cell divides?
a. A new cell plate and wall forms in the middle of the cell and two new cells are formed.
b. The two cells twist apart.
c. The membrane pinches shut in the middle of the cell and the cells are split apart.
d. Plant cells do not divide.
Which of the following is NOT a result of cell division?
a. reproduction
c. growth
b. nutrition
d. repair
How long does it take a cell to complete the cell cycle?
a. 8 minutes
b. 1 year
c. 24 hours
d. The time it takes depends on the type of cell that is dividing.
Matching
Match each phase or stage name with the correct letter from the diagram.
____
____
____
____
____
____
____
1.
2.
3.
4.
5.
6.
7.
mitotic phase
interphase
G1
G2
mitosis
S
cytokinesis
Match each activity to the correct phase of mitosis. You may use the same answer more than once.
a. prophase
b. metaphase
c. anaphase
d. telophase
____ 8. Chromosomes line up single file at the middle of the cell.
____ 9. Two identical nuclei form.
____ 10. Sister chromatids separate.
____ 11. Spindle fibers begin to form and the nuclear membrane begins to break down
____ 12. Spindle fibers break down.
•
•
•
•
•
•
Mendelian Genetics
The father of genetics is Gregor Mendel
Genetics: is the science of heredity
Inheritance, or heredity is the passing of traits to the next generation.
Mendel performed cross-pollination in pea plants by:
Transferring a male gamete from a �lower of one pea plant to the female reproductive organ in
a �lower of another pea plant
Mendel followed various traits in the pea plants he bred.
Mendel experiment:
The Blending Concept of inheritance (pre-mendelian ideas):
•
•
Most plant and animal breeders acknowledged that both sexes contribute equally to a new
individual, they thought that parents of contrasting appearance always produced offspring of
intermediate appearance.
Weakness of this theory: when the traits of contrasting appearance (pure traits) reappeared in
future generation, the breeders mistakenly attributed this to instability in the genetic material.
A particulate theory of inheritance (Mendelian theory):
•
•
Mendel's theory of inheritance is called a particulate theory because it is based on the existence
of minute particles, or hereditary units, that we now call genes.
Inheritance involves the reshuf�ling of the same genes from generation to generation.
Lesson 3: Mendelian patterns of inheritance and human disease:
Many traits and disorder(disease)in human and other organisms are genetic in origin and follow
Mendel’s laws these traits are often controlled by a single pair of alleles on the autosomal
chromosomes.
Autosome: is any chromosomes other than a sex (X or Y)
Autosomal patterns of inheritance
Autosomal dominant disorder
Autosomal recessive disorder
AA → affected
AA → normal
Aa → affected
Aa → carrier
aa → unaffected
Aa → affected
Autosomal recessive disorder
Methemoglobinemia
•
•
•
•
Hemoglobin: the main oxygen –carrying protein in the blood
bright red when carrying oxygen.
Hemoglobin converted at a slow rate to an alternate form called
methemoglobin which has bluish color, oxygen- poor blood.
Methemoglobinemia: is relatively harmless disorder that results
from accumulation of methemoglobinemia, individual with
Methemoglobinemia are unable to clear the abnormal blue
protein from their blood causing their skin to appear bluish
purple.
Cystic Fibrosis
•
•
•
Caused by a defect in gene on chromosome number 22 the
enzyme normally converts methemoglobinemia back to
hemoglobin
Albinism
•
People with albinism have either a partial or complete lack of
pigment or coloring in their eyes, skin or hair due to mutation in
gene on chromosomes 11.
Affects the mucus-producing glands, digestive enzymes, and
sweat glands.
CF occurs due to the defective Chloride ions channel that is coded
by gene on chromosome 7, so chloride ions absorbed into the cells
of a person with cystic �ibrosis but are excreted in the sweat.
Without suf�icient chloride ions in the cells, a thick mucus is
secreted and block the tiny respiratory pathways in the lungs
Phenylketonuria
•
•
•
Known as PKU: which is an autosomal recessive disorder that
affect nervous system development.
PKU is caused by a change in the phenylalanine hydroxylase
(PAH) gene on the chromosome number 12 , that lead to lack of
enzyme needed to break down phenylalanine.
If the newborn baby detected of PKU he will develop normally if
placed on a diet of phenylalanine which must be continued until
the brain is fully developed
Autosomal dominant disorder
Achondroplasia disease (Dwar�ism)
•
Huntington disease
A genetic condition in which the gene that affect bone growth is
abnormal causes small body size and limbs that are comparatively
short.
•
•
Huntington disease is a neurological disorder that leads to
progressive degeneration of brain cells. The disease is caused by a
mutated copy of the gene for a protein called huntingtin.
There is no effective treatment, and death comes 10 to 15 years
after the onset of symptoms.
Osteogenesis imperfecta
•
•
•
Osteogenesis (L. os, "bone"; genesis, "origin") imperfecta is an autosomal dominant genetic disorder that results in weakened, brittle bones.
Although at least nine types of the disorder are known, most are linked to mutations in two genes necessary for the synthesis of type I
collagen, one of the most abundant proteins in the human body.
Osteogenesis imperfecta leads to a defective collagen I that causes the bones to be brittle and weak. Because the mutant collagen can cause
structural defects even when combined with normal collagen I, osteogenesis imperfecta is generally considered to be dominant.
How to use a Punnett Square
A Punnett Square is a helpful tool that helps to predict the variations and probabilities that can come from cross breeding. This includes predicting crossing plants, animals, even humans with each other. Typically, Punnett Squares are used with Mendelian Inheritance: Mendel was the scientist who helped pioneer genetics and give us our basic, fundamental understanding of how traits work. Key Terms: Genotype: The genetic makeup of the organism, what you can find when you look at the DNA Phenotype: The physical makeup of the organism, the characteristics you can see Note: Genotype and Phenotype are not the same! What you see with the phenotype maybe different in the genotype, that’s why the Punnett is important to see that! Homozygous: When both alleles are the same type, either both dominant or both recessive Heterozygous: When the alleles differ in type, with one being dominant and one being recessive. Dominant alleles will almost always mask recessive alleles. Dominant allele: The trait that has a higher probability of occurring and more likely to been seen Recessive allele: The trait that has a lower probability and may not been seen physically How a Punnett Square Works: (In this example, let’s use a heterozygous couple with eye color) Here is where I write down the letters that represent my couple. Because they are heterozygous, I use one capital letter and one lower letter since they have both traits in their genes. Now, I’m gonna carry each letter over from either the top or the side until I have two letters in one box. This creates my predicted results! From here you must use a little math as seen on the other page. B b B b BB Bb Bb bb Here I am making a legend to help me visualize which trait is Dominant and which is Recessive. Dominant is always a capital letter and Recessive is always a lower-­‐case letter. Legend: B: blue eyes b: brown eyes Now, based on our Punnett Square, we have determined the genotype of the possible children. So, we have: How to use a Punnett Square
1 out of 4 squares was BB: this means ¼ will have two dominant alleles (homozygous) 2 out of 4 squares was Bb: this means ½ will have a dominant and recessive allele (heterozygous). 1 out of 4 squares was bb: this means ¼ will have two recessive alleles (homozygous) Now let’s look at the same square but determine the phenotype of the children: B B b
b BB Bb Here I am going to keep the same legend to help me remember what each letter means and paying attention to what the physical trait is. Remember, upper case means Dominant and lower case means Recessive. Bb bb Legend: B: blue eyes B: brown eyes Since upper case letters represent my dominant traits I know they will appear as the physical trait. In this case since both letters are dominant no alleles are competing, making the physical trait blue eyes Since lower case letters represent my recessive traits I know that they will usually be hidden by other dominant traits. H
OWEVER, b ecause b oth alleles are recessive, nothing will mask either recessive allele. Therefore, the eyes will appear brown So, what about this box? This represents a heterozygous combination, meaning that there is one dominant allele and one recessive allele. Remember that a dominant trait will always mask a recessive trait, so while you may have each allele, it will be the dominant trait that you see. Therefore, in this case what you will see are blue eyes even though there is an allele containing brown eyes. Bb How to use a Punnett Square
Now we can say our phenotype is: 1 out of 4 squares was bb, meaning that the physical trait is brown eyes 3 out of 4 squares were BB or Bb, and since the capital letter is dominant, we will physically see blue eyes Sometimes we write our predicted squares as fractions, thus you get: Genotype: Phenotype: 1 /4 BB 3 /4 Blue eyes 1 /2 Bb 1 /4 Brown eyes 1 /4 bb While the couple can have three different genotypes for kids, there are only two phenotypes they can have, with a majority predicting the child will have blue eyes. So why highlight predict? Well life is messy and sometimes the predictions aren’t perfect, but we use this as a basic tool to help us figure out traits. Fun fact: this example is a monohybrid, meaning you are only predicting with one trait, but did you know you can predict two linked traits at once? That’s called dihybrid, and it’s like doing eye and hair color at the same time! CHECK TIME! See if you can solve the following scenario! Consider the traits of hair color with black hair seen as a dominant trait and red hair as a recessive trait. A father has black hair but is heterozygous for both traits, while the mother is homozygous for the trait of red hair. Predict the potential genotypes and phenotypes for the offspring they can have. A a a a Aa aa Aa aa Answer: Father: One capital, One lower case letter (Aa) Mother: Two lower case letters (aa) Genotype: 2 out of 4 boxes will be heterozygous (Aa), 2 out of 4 will be homozygous recessive (aa) Phenotype: 2 of the 4 children will have black hair, 2 out of 4 will have red hair Practice with Punnett Squares
A. Genotype and phenotype
Living things with two parents have two alleles for each gene.
•
Genotype = an individual’s allele combination
•
Phenotype = the visible trait that the alleles cause
EXAMPLE
A gene in peas affects plant height. Different combinations of two alleles (T and t) can make a plant
tall or short.
Genotype (allele combination) Phenotype (visible trait)
TT
tall
Tt
tall
tt
short
PRACTICE
1.
A gene in dogs makes their coat furnished or smooth. There are
two alleles for this gene. In Mutt Mixer, the alleles are shown as
pictures. Another way to represent the alleles is with the letters
F and f.
Furnished (F)
Smooth (f)
Fill in the table. (Tip: Use Mutt Mixer to input the phenotype and see the genotype)
Genotype (allele combination) Phenotype (visible trait)
FF
Ff
ff
2. If you know an individual’s genotype, you can predict its phenotype. But this doesn’t always work
in the reverse. That’s because for some phenotypes, there is more than one possible genotype.
Fill in the table.
Phenotype
furnished
smooth
All Possible Genotypes
B. Dominant and Recessive inheritance
Some traits follow predictable inheritance patterns. For example, for pea height, tall (T) is dominant,
and short (t) is recessive. All that means is this:
•
Dominant: it takes one T allele to cause the tall phenotype, no matter what the other allele is
•
Recessive: it takes two t alleles to cause the short phenotype
PRACTICE
3. A gene in pea plants affects seed color. Circle the best answers:
a. It takes two y alleles to cause the green phenotype. y is ( dominant / recessive )
b. It takes one Y allele to cause the yellow phenotype. Y is ( dominant / recessive )
D. Modeling a cross
If you know the genotypes of two parents, you can make a model to see what the possible
genotypes would be for their offspring. Then from the offspring genotypes, you can figure out the
phenotypes.
EXAMPLE
This model shows a cross between
two pea plant parents:
Parent phenotypes:
Parent genotypes:
Possible gametes:
T
Tall
Short
Tt
tt
t
t
t
—Offspring—
Possible allele
combinations:
Tt
Tt
tt
tt
Phenotypes:
Tall
Tall
Short
Short
E. Punnett squares
A different way to model a cross is with a Punnett square. This model has the possible gametes from
one parent along the left side, and the possible gametes from the other parent along the top. Each
square shows a possible allele combination in the offspring.
EXAMPLE
This Punnett square shows
another way to model the
example cross from section D.
Parent phenotypes:
Parent genotypes:
Tall
Short
Tt
tt
t
—Punnett square—
t
t
t
T
T
Tt
Tt
t
t
tt
tt
Step 1. Fill in the
gametes
Step 2. Fill in the possible
allele combinations
F. Calculating probability
Dominant, recessive, and co-dominant traits follow predictable inheritance patterns. You can use a
Punnett square to predict the chances (or probability) of offspring having each possible genotype
and phenotype.
EXAMPLE
This Punnett square has 4 squares, which together represent all the possible genotypes for offspring
from this cross. So for each possibility, the probability is ¼, or 25%. Together, the possibilities add up
to 1 (¼ + ¼ + ¼ + ¼), or 100% (25% + 25% + 25% + 25%).
Probability as a fraction:
t
T
t
Tt
Tt
tall
Probability as a percent:
t
¼
t
Tt
tall
¼
tt
¼ tt ¼
short
short
t
T
Tt
Tt
25%
25%
tall
tall
t
tt
tt
25%
25%
short
short
or
tt
In the Punnett square above, two squares have a Tt genotype, which makes a tall phenotype. To
calculate the probability of this combination, you can add the values of the squares together.
Probability of tall phenotype (T t):
25% + 25% = 50%
(or)
¼+¼=½
You can do the same for the short phenotype (t t):
25% + 25% = 50%
(or)
¼+¼=½
These calculations tell us that if these two parents make an offspring, there is a 50% (or 1 in 2) chance
that it will be tall, and a 50% (or 1 in 2) chance that it will be short.
H. Independent assortment
In the earlier examples and problems, you modeled one gene at a time. But gametes (reproductive
cells, like eggs and sperm) get one allele for each gene. Importantly, different genes are inherited
independently of one another. This idea is known as independent assortment.
The process that shuffles alleles into all their possible combinations in reproductive cells is
recombination. Recombination contributes to genetic variation in a population.
EXAMPLE
In pea plants, separate genes affect plant height and seed color. When a plant makes gametes, the
allele a gamete gets for height has no effect on the allele it gets for seed color.
As this model shows, every allele combination is possible in the gametes:
Phenotype:
Genotype:
Possible gametes:
Tall, Yellow seeds
TtYy
TY
Ty
tY
ty
I. Two-factor cross: two traits in one Punnett square
You can use a model, such as Punnett square, to track the possible allele combinations offspring
can have for two (or more) genes. Since alleles for different genes are inherited independently from
each other, you need to account for many more possible allele combinations in the offspring!
EXAMPLE
This Punnett square models a two-factor cross:
Parent phenotypes:
Tall, Yellow seeds
Parent genotypes:
TtYy
Possible gametes:
TY
tY
Ty
ty
Short, Yellow seeds
ttYy
tY
tY
ty
tY
ty
tY
ty
ty
Step 1: Figure out all
possible gametes
tY
ty
tY
ty
TY
TY
TtYY
TtYy
TtYY
TtYy
Ty
Ty
TtyY
Ttyy
TtyY
Ttyy
tY
tY
ttYY
ttYy
ttYY
ttYy
ty
ty
ttyY
ttyy
ttyY
ttyy
Step 2. Fill in the gametes
Step 3. Fill in the allele combinations
From here, you could calculate the probability for each phenotype. Since there are 16 cells in the
Punnett square, the probability for each cell is 1/16.
For example, the genotype ttyy appears in 2 cells.
So the probability of getting a short offspring with green seeds is 1/16 + 1/16 = 2/16 (or 1/8)
PUNNETT SQUARE CHEAT SHEET
Below is a sampling of Punnett Square problems that you will be expected to solve. In
order to do this, you will also have to understand the meaning of the terms below.
ƒ
Genotype: The letters that make up the individual. E.g. TT or Tt
ƒ
Phenotype: The physical characteristics of the particular trait. E.g. Tall or short
ƒ
Dominant trait: Signified by capital letter-E.g. T. If the traits you are using are dominant or recessive, this
trait will "overpower" the recessive trait and will be expressed. E.g. Tt
ƒ
Recessive trait: Signified by small case letter-e.g. t. An organism with a recessive allele for a particular
form of a trait will have that form only when the dominant allele for the trait is not present
ƒ
Homozygous: Has same letters. E.g. TT or tt (same alleles for trait)
ƒ
Heterozygous: Has different letters. E.g. Tt (different alleles for trait)
ƒ
Purebred trait: Also known as true breeding. Individuals genotype is homozygous and will only make one
type of gamete. E.g TT will always produces T, and T. tt will always produce t, and t.
ƒ
Gamete: sex cells. Represented by letter N (meaning they are haploid-contain half the chromosomes
ƒ
P generation: The parental generation (Usually the first one in a genetic cross)
ƒ
F1 generation: The first generation of offspring from P generation (means first filial: Latin for "son")
ƒ
F2 generation: The second generation of offspring from P generation (means first filial: Latin for "son")
ƒ
Monohybrid Cross: Also known as a Single-Factor Cross. Only one trait is used in the genetic cross.
E.g. T=Tall, t=short. Example: Tt x Tt
ƒ
Dihybrid Cross: Also known as a Two-factor Cross. Two trait are used in the genetic cross. E.g. T=Tall,
t=short & B=Black fur, b=white fur. Example TtBb x TTBB
ƒ
Sex-linked trait: Genes located on the sex-chromosomes called sex-linked genes. Usually found on the
X chromosome. X-linked alleles are always expressed in males because males have only one X
chromosome.
ƒ
Genotypic ratios: The ratio of different genotype in the offspring from a genetic cross. E.g 1:2:1
ƒ
Phenotypic ratios: The ratio of different phenotypes in the offspring from a genetic cross. E.g 3:1
1. Which of the following is a heterozygous dominant genotype?
a)
b)
c)
d)
GG
gg
GGG
Gg
2. In Mendel's pea plants, the homozygous recessive phenotype was white flowers. If Mendel crossed two homozygous
recessive pea plants, what color flowers would be seen in the offspring?
a)
b)
c)
d)
white and purple
white
purple
lavender
3. Green peas are dominant (G) to yellow peas (g). What is the genotype for a hetereozygous dominant offspring?
a)
b)
c)
d)
Gg
gg
GG
gG
4. Dominant alleles are represented by a(n)
a)
b)
c)
d)
phenotype
lower case leter
upper case leter
Punnet square
5. What type of traits "show up" in a popula�on more o�en?
a)
b)
c)
d)
dominant
recessive
Punnet squares
alleles
6. A heterozygous dominant trait can be writen as BB.
a) True
b) False
7. D = dimples
d = no dimples
What is the genotype for a homozygous recessive offspring?
a)
b)
c)
d)
DD
Dd
dd
dD
8. Round seeds are dominant to wrinkled seeds.
What is the genotype for a homozygous dominant offspring?
R = round / r = wrinkled
a)
b)
c)
d)
RR
Rr
rr
rR
9. If two purebred species (BB) are crossed, what percentage of their offspring would be BB?
a)
b)
c)
d)
25%
50%
75%
100%
10. What do you call the physical expression of a gene?
a)
b)
c)
d)
genotype
dominant
phenotype
allele
11. Short hair (S) is dominant to long hair (s).
What is the genotype for an offspring with long hair?
a)
b)
c)
d)
SS
Ss
ss
sS
12. What does "genotype" refer to?
a)
b)
c)
d)
the chromosomes of an organism
the gene�c make-up of an organism
the type of gene in ques�on
the physical expression of genes
13. Mendel's First Law states that the factors that determine physical traits are carried only by sperm cells.
a) true
b) false
14. When two organisms are crossed, the offspring are referred to as
a)
b)
c)
d)
the F2 genera�on
recessive
the F1 genera�on
a genotype
15. Mendel believed that physical traits of pea plants are determined by
a)
b)
c)
d)
inheritance of factors from both parents
inheritance of factors from the male parent only
inheritance of factors from one parent
inheritance of factors from the female parent only
16. A chart used to determine the offspring of a gene�c cross is called a
a)
b)
c)
d)
cross chart
Punnet square
periodic table
Gene�c square
17. Mendel's Second Law states that alleles randomly and independently segregate into an organism's gametes.
a) true
b) false
18. Incomplete dominance results in
a)
b)
c)
d)
a trait that is a mix of those seen in the parent
the offspring having a different trait than either parent
both of the choices
neither of the choices
19. If snapdragons demonstrate incomplete dominance in flower color, what would be the result of a cross between a
red-flowered snapdragon with a white-flowered snapdragon?
a)
b)
c)
d)
All the offspring will have white flowers
All the offspring will have pink flowers.
All the offspring will have red flowers.
Three-fourths of the offspring will have red flowers and one-fourth will have white flowers.
20. The “father of modern gene�cs” is:
a)
b)
c)
d)
Charles Darwin
Gregor Mendel
Francis Crick
James Watson
21. If an offspring is said to be homozygous recessive, which of the following could be its
genotype?
a)
b)
c)
d)
Rr
Tt
ss
Ss
22. Genotype refers to:
a) The gene�c make-up of an organism
b) The physical make-up of an organism
c) The gene�c and physical make-up of an organism
23. If fur colour in mice is caused by the following: B= black and b= brown, choose the genotype
for the organism which will have brown fur. (Assume black is dominant)
a)
b)
c)
d)
BB
Bb
bb
A or B
24. A specific form of a characteris�c that can be inherited is referred to as:
a)
b)
c)
d)
e)
Gene
Chromosome
Hybrid
Trait
muta�on
25. Assume that in mice, B=black fur, b = brown fur. If a heterozygous black mouse mates with a
homozygous brown mouse, what percent of their offspring will have black fur?
a)
b)
c)
d)
25%
50%
75%
100%
26. What characteris�c describes an individual that carries two different alleles for a given
characteris�c?
a)
b)
c)
d)
Homozygous
Heterozygous
Dominant allele
Recessive alleles
27. Which one of the following would have a different phenotype from the others?
a)
b)
c)
d)
Rr
rR
RR
rr
28. Based off this Punnet square, what frac�on of the offspring will have wrinkled, yellow seeds?
a)
b)
c)
d)
9/16
3/16
1/16
16/16
29. A male beetle has the genotype Ttbb. If this beetle mates with a female with genotype TTBb, what is the chance their
offspring will have the genotype TtBb?
a)
b)
c)
d)
12.5%
25%
50%
75%
30. What is the genotype for a pea plant heterozygous for round seeds (R), and homozygous recessive for green seeds
(y)?
a)
b)
c)
d)
Ry
RRyy
RrYy
Rryy
31. What frac�on of offspring from the cross AaBB x Aabb will be heterozygous for both traits?
a)
b)
c)
d)
1/16
1/4
1/2
3/16
32. Cross Two Homozygous plants
(RRYY x rryy)
R = round seeds, r = wrinkled seeds Y = yellow seeds, y = green seeds
What percent will have Round and Yellow seeds?
a)
b)
c)
d)
0%
25%
50%
100%
33. In fruit flies the presence of wings (W) is dominant to the absence of wings (w), and red eyes (R) aredominant to
brown eyes (r). A wingless fly that is heterozygous for eye color is crossed with a fly that isheterozygous for wings and has
brown eyes. What is the probability that the offspring would behomozygous recessive for wings and eye color?
a)
b)
c)
d)
25%
50%
75%
100%
34. In tomatoes, red fruit (R) is dominant to yellow fruit (r), and tall plants (T) are dominant to short plants(t). What
percentage of the offspring from a RRTT X rrt cross are expected to be RrTt?
a)
b)
c)
d)
25%
50%
75%
100%
35. Two traits in ducks-beak size and leg color. G, the allele for giant beak size, is dominant to g, the allele for a small
beak. Y, the allele for yellow legs is dominant to y, the gene for blue legs. Two ducks, that are both heterozygous for both
traits cross. What will be the phenotypic ra�o?
a)
b)
c)
d)
3:1:3:1
4:4:4:4
9:3:3:1
6:2:2:6
36. In watermelons, the allele for solid green color (G) is dominant over the allele for striped patern (g). Short shape(S) is
dominant over long shape (s). A cross is made between a watermelon that is homozygous for green color and short
shape and watermelon that has a striped patern and long shape. What is the genotype of each parent?
a)
b)
c)
d)
GGSS / ggss
GgSs / ggss
GgSs / GgSs
GGSS / Ggss
37. In pea plants, green pods (G) are dominant to yellow pods (g), and tall plants (T) are dominant to short plants (t).
What frac�on of offspring from a GGTT x GgTt cross are expected to be GGTt?
a)
b)
c)
d)
1 out of 16
4 out of 16
8 out of 16
16 out of 16
38. Two fruit flies, heterozygous for red eye color (Rr) and yellow body color (Yy), are crossed. What is the probability the
offspring will be homozygous recessive for eye color and body color?
a)
b)
c)
d)
0/16
1/16
4/16
8/16
39. Which statement represents dihybrid crosses?
a)
b)
c)
d)
Dihybrid crosses represent one trait from three different parents
Dihybrid crosses explain how traits are inherited independently of other traits
Dihybrid crosses are two genes from two different parents
Dihybrid crosses represent two traits from parent organisms
40. Two guinea pigs that are heterozygous for brown fur (Bb) and short fur (Ss) are crossed. What is the probability the
offspring will be homozygous dominant for fur color and fur length?
a)
b)
c)
d)
1/4
1/8
1/16
1/2
41. In guinea pigs, the allele for short hair (S) is dominant over the allele for long Hair (s). The allele for black hair (B) is
dominant over the allele for brown hair (b). A cross is made between two guinea pigs which are both heterozygous for
short, black hair. How many of the offspring will have long black hair?
a)
b)
c)
d)
3
9
1
2
Use this diagram to answer ques�on 42 and 43
42. What percentage of the offspring will be purebred dominant?
a)
b)
c)
d)
0%
25%
50%
75%
43. What percentage of the offspring will be heterozygous dominant?
a)
b)
c)
d)
100%
75%
50%
25%
Use this diagram to answer ques�ons 44, 45, 46
44. What is the percentage of a homozygous dominant offspring? (DIAGRAM 2)
a)
b)
c)
d)
75%
50%
25%
0%
45. How many of the offspring could be homozygous recessive? (DIAGRAM 2)
a)
b)
c)
d)
0
1 out of 4
2 out of 4
3 out of 4
46. What percentage of the possible offspring will be hybrids? (DIAGRAM 2)
a)
b)
c)
d)
25%
50%
75%
100%
47. What genotype is missing from this Punnet Square?
a)
b)
c)
d)
RrYy
RRYY
rryy
RrYY
48. Being right-handed (R) is dominant over being le�-handed(r) and having freckles (F) is dominant over not having
freckles (f). Two parents are both heterozygous for both traits. Using the completed Punnet Square above, what
probability of offspring(s) are right-handed with freckles?
a)
b)
c)
d)
1/16
4/16
3/16
9/16
_________________________________________
1. In Mendel’s pea plants, purple flowers (P) are heterozygous dominant over white flowers (p).
Create a Punnet square for a cross between a homozygous purple flowering plant and a
homozygous white flowering plant. What is the phenotypic ra�o? What is the genotype
ra�o?
Create a Punnet Square for a cross between a heterozygous purple flowering plant and a
homozygous white flowering plant. What is the phenotype ra�o? What is the genotypic
ra�o?
2. Set up a Punnet square using the following informa�on:
•
•
•
•
D = dominant allele for tall plants
D = recessive allele for dwarf plants
W = dominant allele for purple flowers
w = recessive allele for white flowers
Cross a homozygous dominant parent (DDWW) with a homozygous recessive parent (ddww)
What is the probability of producing tall plants with purple flowers? ___________________
Possible genotype? _________________________
What is the probability of producing dwarf plants with white flowers?___________________
Possible genotype? _________________________
What is the probability of producing tall plants with white flowers?_____________________
Possible genotype? _________________________
What is the probability of producing dwarf plants with purple flowers?_____________________
Possible genotype? _________________________
3. Set up a Punnet square using the following informa�on:
•
•
•
•
B = dominant allele for black fur in guinea pigs
b = recessive allele for white fur in guinea pigs
R = dominant allele for rough fur in guinea pigs
r = recessive allele for smooth fur in guinea pigs
Cross a heterozygous parent (BbRr) with a heterozygous parent (BbRr)
What is the probability of producing guinea pigs with black, rough fur? ___________________
Possible genotype? _________________________
What is the probability of producing guinea pigs with black, smooth fur?___________________
Possible genotype? _________________________
What is the probability of producing guinea pigs with white, rough fur?_____________________
Possible genotype? _________________________
What is the probability of producing guinea pigs with white, smooth fur?_____________________
Possible genotype? _________________________
1. In a pedigree, a square represents a male. If it is darkened he has hemophilia; if clear, he had normal blood clo�ng.
a) How many males are there?
b) How many males have hemophilia?
2. A circle represents a female. If it is darkened, she has hemophilia; if open she is normal.
a) How many females are there?
b) How many females have hemophilia?
3. A marriage is indicated by a horizontal line connec�ng a circle to a square.
a) How many marriages are there?
4. A line perpendicular to a marriage line indicates the offspring. If the line ends with either a circle or a square, the
couple had only one child. However, if the line is connected to another horizontal line, then several children were
produced, each indicated by a short ver�cal line connected to the horizontal line. The first child born appears to the
le� and the last born to the right.
b) How many children did the first couple (couple in row I) have?
c) How many children did the third couple (couple in row III) have?
5. Level I represent the first genera�on; level II represents the second genera�on.
a) How many genera�ons are there?
b) How many members are there in the fourth genera�on?
1. If a child has an autosomal dominant trait, what can you say about the parents?
____________________________________________________________________________________________
____________________________________________________________________________________________
2. If two parents have an autosomal dominant trait, what can you say about their children?
____________________________________________________________________________________________
____________________________________________________________________________________________
3. If two parents have an autosomal recessive trait, what can you say about their children?
____________________________________________________________________________________________
____________________________________________________________________________________________
4. If two parents do not have an autosomal recessive trait, what can you say about their children?
____________________________________________________________________________________________
____________________________________________________________________________________________
5. Can autosomal recessive traits skip genera�ons?
____________________________________________________________________________________________
____________________________________________________________________________________________
A. Methemoglobinemia
B. Cys�c Fibrosis
C. Albinism
D. Phenylketonuria
E. Osteogenesis imperfecta
F. Hun�ngton disease
G. Achondroplasia disease (Dwarfism)
1. Autosomal dominant gene�c disorder that results in weakened, britle bones due to muta�on in two genes necessary
for synthesis of Type (I) collagen. ( )
2. A gene�c condi�on in which the gene that affects bone growth becomes abnormal and causes small body size and
limbs that are compara�vely short. ( )
3. A par�al or complete lack of pigment or coloring in their eyes, skin, or hair. (
)
4. A neurological disorder that leads to progressive degenera�on of brain cells, caused by a mutated copy of the gene for
a specific protein. ( )
5. A disorder that causes skin to appear bluish purple. (
)
6. A disorder that causes secre�on of thick mucus that blocks �ny respiratory pathways in the lungs. (
7. Autosomal recessive disorder that affects the nervous system development. (
)
)
(22 – 7 – 11 – 12)
Disease
Albinism
Phenylketonuria
Methemoglobinemia
Cys�c Fibrosis
Affected chromosome
1) The pedigree above tracks the presence of attached earlobes
through a family's generations. Having attached earlobes is an
autosomal recessive trait.
If individual III-6 married a man who was homozygous for
unattached earlobes, what is most likely to be true regarding their
children?
a) The children would all have partially attached earlobes.
b) All the female children will have unattached earlobes, and all
the male children will have attached earlobes.
c) All of their children would have unattached earlobes.
d) All of their children would have attached earlobes.
2) The pedigree above tracks the presence of attached earlobes
through a family's generations. Having attached earlobes is an
autosomal recessive trait.
If individuals I-1 and I-2 had a fourth child, what is the chance that
the child would have attached earlobes?
a) 100%
b) 50%
c) 0%
d) 75%
3) The pedigree above tracks the presence of attached earlobes
through a family's generations. Having attached earlobes is an
autosomal recessive trait.
What is the genotype of individual I-1?
a) EE
b) XEY
c) XeY
d) ee
e) Ee
4) The pedigree above tracks the presence of attached earlobes
through a family's generations. Having attached earlobes is an
autosomal recessive trait.
What is the genotype of individual II-3?
a) EE
b) XeY
c) ee
d) XEY
e) Ee
5) The pedigree above tracks Duchenne Muscular Dystrophy (DMD)
through several generations. DMD is an X-linked recessive trait.
If individuals I-1 and I-2 had another son, what is the chance that he
would have DMD?
a) 50%
6) The pedigree above tracks Duchenne Muscular Dystrophy (DMD)
through several generations. DMD is an X-linked recessive trait.
Based on the pedigree, which of the following is true?
a) If individual III-1 marries an unaffected, non-carrier female,
none of their offspring will have DMD.
b) 0%
b) Individual II-1 is a carrier for DMD.
d) 100%
d) If individuals II-4 and II-5 have a fourth child, there is a 50%
c) 25%
c) Individual II-3 has a genotype of XDY.
chance that it will not have DMD.
7) The pedigree above tracks Duchenne Muscular Dystrophy (DMD)
through several generations. DMD is an X-linked recessive trait.
What is the genotype of individual II-2?
a) XDXD
b) XdY
c) XDXd
d)
XdXd
8) The pedigree above tracks Duchenne Muscular Dystrophy (DMD)
through several generations. DMD is an X-linked recessive trait.
If individual II-3 has a child with a carrier woman, what is the
percent chance that the child will be a daughter with DMD?
a) 100%
b) 25%
c) 50%
d) 0%
9) If individuals II-1 and II-2 have a fourth child, what is the
probability that the child will have dimples?
a) 100%
b) 75%
c) 50%
d) 25%
10)The pedigree above tracks the presence of dimples through a
family's generation. Having dimples is an autosomal dominant trait.
What is the phenotype of individual III-4?
a) DD
b) No dimples
c) dd
d) Dimples
11) The pedigree above tracks the presence of dimples through a
family's generation. Having dimples is an autosomal dominant trait.
Which of the following individuals is correctly matched with its
genotype?
a) III-2 → Dd
b) II-3 → dd
c) II-2 → DD
d) I-1 → Dd
12)The pedigree above tracks the presence of dimples through a
family's generation. Having dimples is an autosomal dominant trait.
If individual III-3 married a woman who was heterozygous for
dimples, what is the percent chance their children will have
dimples?
a) 0%
b) 25%
c) 100%
d) 75%