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Accelerated Biology Lab
Name:______________________________
Date:_____________
Meiosis and Fertilization Lab
Background:
Meiosis is the kind of cell division that produces special haploid cells called gametes. In meiosis,
chromosomes are divided between cells so that the resulting gametes only have half the amount DNA found in
a body cell in that organism. As a result of fertilization, which is the uniting of the sperm and egg, the
offspring of organisms have a mixture of both parents’ genes. The offspring receive one set of chromosomes
and genes from its mother in the egg and one set from its father in the sperm. This variety allows for natural
selection to occur.
In this lab, you will simulate meiosis and fertilization and explore the variety of traits that characterize
the offspring. An organism’s physical traits are called its phenotype. These traits or phenotypes are due to
the organism’s genotype, or genetic makeup. Your genes determine your traits. Genes often come in two
forms, dominant alleles and recessive alleles. When you have a dominant allele, represented by a capital
letter, you possess the dominant trait or phenotype. The recessive phenotype only occurs when the individual
doesn’t have any dominant alleles and has two recessive alleles, represented by lower case letters.
Because each person gets two copies of a gene, one from each parent, there are three possible
genotypes that individuals can have. The homozygous dominant genotype occurs because the dominant
allele for that gene was received from both parents. The heterozygous genotype occurs because the
dominant allele for that gene was received from one parent and the recessive from the other. Both
homozygous dominant and heterozygous individuals share the same dominant phenotype because they have
dominant alleles. Homozygous recessive genotype occurs because the recessive allele for that gene was
received from both parents, resulting in the recessive phenotype. Let’s use the gene for hair color as an
example. In humans, the brown hair gene, represented B, is dominant to the blond hair gene, b. If you have
the homozygous dominant genotype, BB, you have the brown hair phenotype. If you have the heterozygous
genotype, Bb, you have the brown hair phenotype. If you have the homozygous recessive genotype, bb, you
have the blond hair phenotype. In this lab, you will determine your genotypes and phenotypes for several
traits. You will then predict the genotypes and phenotypes of you and your partner’s possible children.
Pre-Laboratory Questions: (Answer these in your lab notebook)
1. Why do the processes of meiosis and fertilization result in genetically different offspring?
2. Why is genetic variation beneficial to a species?
3. How does the term genotype differ from the term phenotype?
Procedure: (You DO NOT need to copy this into your lab notebook)
Part 1: Determining the Parent’s Phenotypes and Genotypes
1. You teacher will randomly assign you a partner. This partner will be the other parent of the “offspring” you
will be creating in this lab. Because sperm and egg must come together in fertilization to create an offspring,
one parent must be male and one must be female. If your partner is the same sex as you, decide who will be
the member of the opposite sex for the duration of the lab.
2. Examine the drawings of genotypes and phenotypes for 6 traits on the next page. Determine your
phenotype for the 6 traits (as in what traits you actually display). Based on your phenotype, determine your
genotype. Remember the dominant phenotype can be caused by homozygous dominant or heterozygous
genotypes. If you show the homozygous dominant phenotype, flip a coin to determine if you are homozygous
dominant or heterozygous. If you flip a head, you are homozygous dominant. If you flip a tail, you are
heterozygous. Record your phenotypes and genotypes in Table 1 in your lab notebook. Remember to use the
sex that was determined in step 1.
3. Copy your partner’s genotype and phenotype information in Table 1 in your lab notebook.
4. On your chromosome sheet, write your name on the parent lines of all of the chromosomes. These
chromosomes represent a homologous pair of chromosomes found in your body cells. Write the allele for each
trait on the chromosome pair with the corresponding number. Be sure to write only one allele of your
genotype on each side of the chromosome. Remember that each chromosome in the pair contains one of the
two alleles that make up your genotype.
5. On your sheet, cut out each chromosome pair along the heavy line. Then cut down the middle of each
chromosome pair. When you have cut out all of the chromosomes, you should have 12 chromosomes.
Part 2: Determining the Offspring’s Phenotypes and Genotypes
1. Turn over your 12 chromosomes on the desk so that you cannot see the writing. Your partner will do the
same. Randomly flip over one chromosome in each of your 6 chromosome pairs. These are the chromosomes
that were sorted into your gamete.
2. Pair up your flipped over chromosomes with your partners. Examine the alleles. These are the alleles that
the offspring will inherit.
3. Complete Data Table 2 for the “child”. Name the child. Make sure the name of the child corresponds to the
sex chromosomes picked.
4. Repeat steps 1-3 two more times in order to have three “children”.
Copy the data tables below into your lab notebook.
Data Table 1: Traits of the Parents
Parent’s Name:________________________
Trait
1
Genotype
Phenotype
Parent’s Name:________________________
Trait
1
2
2
3
3
4
4
5
5
6
6
Genotype
Phenotype
Data Table 2: Traits of the Children
Child’s Name:________________________
Trait
1
Genotype
Phenotype
Child’s Name:________________________
Trait
1
2
2
3
3
4
4
5
5
6
6
Genotype
Phenotype
Child’s Name:________________________
Trait
1
Genotype
Phenotype
2
3
4
5
6
Analysis Questions: (To be answered in your lab notebook.)
1. Identify and explain which actions you carried out that simulated meiosis and fertilization.
2. Explain why children are genetic mixes of their parents.
3. Explain why it is not always possible to determine your genotype based on your phenotype.
4. Suppose that both parents are homozygous dominant (LL) for lobed ears. Predict the genotypes of each of
their possible children. Explain your reasoning.
5. Suppose both parents are heterozygous (Rr) for the tongue-rolling trait. Predict the genotypes of each of
their possible children. Explain your reasoning.
Conclusion: (To be answered in your lab notebook.)
What kind of conclusions can you draw from this activity? What new information did you learn? How could
this activity be improved in the future?
Chromosome 1: Hairline
Widow’s Peak: WW, Ww
(dominant)
No peak: ww
(recessive)
Chromosome 2: Thumb
Curves back: TT, Tt
(dominant)
Straight: tt
(recessive)
Chromosome 3: Tongue Rolling
Ability to roll: RR, Rr
(dominant)
Inability to roll: rr
(recessive)
Chromosome 4: Ears
Lobed: LL, Ll
(dominant)
Attached: ll
(recessive)
Chromosome 5: Hands
Mid-digital hair: HH, Hh
(dominant)
Lack of mid-digital hair
(recessive)
Chromosome 6: Sex
Female: XX
Male: XY
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