Download Mendel`s Work - Chapter 4 Section 1 Directions: READ pages 110

Mendel’s Work - Chapter 4 Section 1
Directions: READ pages 110-115. When you are finished reading, answer questions 1 – 10.
Heredity: The passing of traits from parents to offspring.
Purebred: The offspring of many generations that has the same traits.
Trait: A characteristic that an organism can pass on traits to its offspring through its genes.
Genetics: The scientific study of heredity.
Gene: The set of information that controls a trait; a segment of DNA on a chromosome that codes for a specific trait.
Allele: The different forms of a gene.
Hybrid: An organism that has two different alleles for a trait: an organism that is heterozygous for a particular trait.
Dominant Allele: An allele whose trait always shows up in the organism when the allele is present.
Recessive Allele: An allele that is masked when a dominant allele is present.
1. Gregor Mendel experimented with hundreds of pea plants to understand the process of _______________. Heredity
2. Summarize the procedure for Mendel’s experiment. (Cross pollinated)
He began with purebred plants. (tall and short), To prevent self-pollination, Mendel removed the stamen (pollen
producing sex cells), Used a brush to brush to remove pollen from white flower an brushed onto the pistils of another.
Allow time for egg cells to fertilize, peas form.
3. In Mendel’s cross for stem height, what contrasting traits did the pea plants in the P generation exhibit? Tall & Short
Stems Height
4. What trait or traits did the plants in F1 generation exhibit? Both Tall
5. When you think of the traits of the parent plants, why is this result surprising?
If half comes from each parent then why did shortness get hidden? Why didn’t the offspring become medium?
6. Contrast the offspring in F1 generation to the offspring in F2 generation.
What did the differences in F1 and F2 show to Mendel?
The individual factors (genes) exist in pairs, where one can be hidden by the other.
7. What is a dominate allele and how are they represented?One whose trait always shows up when the allele is present (R)
8. What is a recessive allele and how are they represented?A trait that is hidden whenever the dominant allele is present (r)
9. Explain how dominant and recessive alleles for the trait of stem height determine whether a pea plant will be tall or short.
If the plant has two dominant alleles for stem height (TT), then it is tall. If the plant is a hybrid (Tt), it is tall.
10. Can a short pea plant ever be a hybrid for the trait of stem height? Why or why not? As part of your explanation, write
the letters that represent the alleles for stem height of a short pea plant.
No, a short plant has two recessive (tt); hybrids have two different alleles for at trait (Tt). A hybrid would appear tall
because the tall allele is dominant.
Probability and Heredity – Chapter 4 Section 2
Directions: READ pages 118 – 123. When you are finished reading, answer the questions below.
Probability: A number that describes howl likely it is that an event will occur.
Punnett Square: A chart that shows all the possible combination of alleles that can result from a genetic cross.
Phenotype: An organisms physical appearance, or visible traits.
Genotype: An organism’s genetic makeup, or allele combinations.
Homozygous: Having two identical alleles for a trait.
Heterozygous: Having two different alleles for a trait.
Codominance: A condition in which neither of two alleles of a gene is dominant or recessive.
1. If you know the parents’ alleles for a trait, how can you use a Punnett square to predict the probable genotypes of the
offspring?
A Punnett square shows all the possible combinations of alleles that coan result from a genetic cross.
2. A pea plant with round seeds has the genotype Rr. You cross this plant with a wrinkled-seed plant, genotype rr. What is
the probability that the offspring will have wrinkled seeds? (Use a Punnett square to help with the prediction.)
50% Punnet square should show two Rr and two rr possibilities
R
r
r
Rr
rr
r
Rr
rr
3. Explain how two organisms can have the same phenotype but different genotypes. Give an example.
A heterozygous organism will have the same phenotype as an organism that is homozygous for a dominant allele.
4. A pea plant has a tall stem, what are its possible genotypes?
TT or Tt
5. Describe the difference between heterozygous and homozygous.
Heterozygous (hybrid) is an organism that has two different alleles for a trait (Ss), where as homozygous means that two
identical alleles. Example (ss)