Reebop Lab
A Reebop is a little marshmallow organism that has 14 chromosomes (7 pairs). It reproduces sexually. Meiosis occurs in the male gonads to make sperm (spermatogenesis) and in female gonads to make eggs (oogenesis). The sperm and eggs (gametes) each have 7 chromosomes due to meiosis. When fertilization occurs, 7 chromosomes are given by each parent, and the baby reebop has 14 chromosomes. The reebop diploid (2n) number is 14 and the haploid (n) number is 7.
Term introduction:
Gonads: Sex organs (ovaries & testes)
Sexual Reproduction: Production of offspring following the union of two gametes (fertilization).
Gametes: Sex cells (egg & sperm)
Meiosis: Series of two cell divisions that reduce chromosome number from diploid to haploid.
Ploidy: Refers to the number of sets of chromosomes in a cell.
Diploid: (2n) Two sets (one from each parent)
Haploid: (1n or n) one set
Traits: Inherited characteristics (i.e. hair color, eye color,height, nose, ears, etc.)
Gene: Segment of DNA that codes for certain proteins
Allele: Alternate forms of the same gene. (One from mom, one from dad)
Genotype: Genetic make-up or allele combination (what’s in their genes)
Homozygous: dominant (AA) or recessive (aa)
Heterozygous: hybrid (Aa)
Phenotype: Physical expression of genotype. (What you see)
Gregor Mendel, considered the father of Genetics, developed two laws of inheritance after many years of research using pea plants.
1. Law of Segregation: allele pairs separate or “segregate” during gamete formation, and randomly unite at fertilization.
2. Law of Independent Assortment: Genes for different traits are inherited independently of each other.
Purpose:
1. To understand the process of meiosis, fertilization, and embryonic development
2. To understand the role of alleles in determining traits of an offspring
3. To understand the difference between genotypes and phenotypes
4. To understand how meiosis and fertilization ensures genetic variation in offspring
5. To observe and analyze Gregor Mendel’s laws of inheritance
Materials:
large marshmallows small colored marshmallows toothpicks
green pipe cleaners red & blue pushpins thumbtacks
paper chromosome set paperclips
Procedure:
1. Observe the mom and dad reebops that your teacher has provided for you.
A) Describe their physical characteristics.
______
______
2. Work in groups of 2 students. Decide who will represent each parent. Remove the paper chromosomes from the envelopes. The “father” should lay the green chromosomes out on the desk from largest to smallest. The “mother” should do the same with the red chromosomes. You have just created a reebop karyotype. Karyotyping is a technique used to analyze the chromosomes of an individual.
B) How many chromosomes does each parent have? ______
Homologous chromosomes are pairs of chromosomes that are the same size and shape and code for the same characteristics (have same genes in same order). One comes from the mom and one comes from the dad.
C) How many pairs of homologous chromosomes does each parent have? ______
3. Notice the letters on each chromosome (ex. #1 A, a; #2 Q, q). These letters (capitol and lower case) represent alleles. Alleles are different forms of a gene for a specific trait.
D) Why does each reebop have two alleles for a given trait? ______
4. Turn the chromosomes over so you cannot see them. Keep them in karyotype order (in pairs, largest to smallest).
5. The "father" should arbitrarily take one green chromosome from each pair and put it in a pile called "sperm."
E) Is the sperm diploid or haploid? ______
F) What type of cell division makes sperm (mitosis or meiosis)? ______
6. The "mother" should arbitrarily take one red chromosome from each pair and put it in a pile called "egg" (or ovum).
G) Is the egg diploid or haploid? ______
H) What type of cell division makes eggs (mitosis or meiosis)? ______
7. Put the extra chromosomes back into the correct envelope.
8. Now, reebop fertilization can occur. Join the sperm and egg (two piles of chromosomes). A reebop zygote has been formed! Flip the chromosomes over so you can read them and arrange them in karyotype order (in pairs, largest to smallest).
I) How many chromosomes does your zygote have? ______
J) How does this compare to the number that each reebop parent had (question B)? ______
K) Is the zygote diploid or haploid? ______
L) What has to happen to the zygote for it to develop into a baby reebop?
______
9. Complete the table 1 below for your baby reebop by analyzing its chromosomes.
· Record the letters on the chromosomes under "alleles."
· The alleles that the baby reebop inherited are called its genotype. If the baby reebop has two of the same alleles (ex. #1AA or aa) it is pure for that trait. If the baby reebop has two different alleles (ex. #1Aa) it is hybrid for that trait.
· Use table 2 to determine the reebops phenotype. The phenotype is the physical characteristic expressed due to the genotype.
Table 1 Baby Reebop
Chromosome / Alleles(letters) / Genotype
(pure or hybrid) / Phenotype
(physical characteristic)
1 / ______
2 / ______
3 / ______
4 / ______
5 / ______
6 / ______
7 / ______
· Use the key the to construct your Reebop.
10. Place the red chromosomes back onto the mother's envelope and green chromosomes back into the father's envelope.
11. Compare your baby reebop with three of its siblings. Is your reebop the same or different than its siblings? ______Give examples of any differences below:
12. Place your baby reebop in the designated nursery area.
Discussion Questions
1. Reebops have a diploid number (2n) of 14. Explain how the diploid chromosome number is maintained from one generation to the next. (In other words, why did the baby reebop have 14 chromosomes instead of 28?)
2. What role does fertilization play in maintaining the diploid number from one generation to the next?
3. For any given trait, how many alleles does a baby Reebop or any organism have? Explain why.
4. Based on the results of the Reebop lab, children from the same parents are not exactly the same; there was a lot of variation among the offspring. Explain why this occurs.
5. The fact that the different alleles were separated during this process and randomly combined during fertilization is an example of which Mendel’s laws of Inheritance?
6. The gene for the number of antennae and the gene for nose color were passed on independently of each other. This process represents which of Mendel’s laws of Inheritance?