Homework 2
Name___________________________________
1. In Potato heads, which is dominant long arms or short arms?________________________
L
2. How did the 2 baby Potato heads get short arms (the recessive trait)?____________
l Ll
_______________________________________________________________________
3. What would a Potato head look like if it had two recessive alleles for arm length?
4. What is a recessive gene? (page 83)
Ll
5. What do we call a gene that gets masked in the presents of another gene?____________
6. What do we call a gene that hides (masks) a recessive gene?______________________
l
7. What does masked mean?_________________________________________________
l
ll
ll
The factors that control each trait exist in pairs. The female parent contributes one factor, while the male parent contributes the other
factor. Finally, one factor in a pair can mask, or hide, the other factor. Recessive genes are masked in the presents of another gene.
1. How do recessive genes get masked?________________________________________________________________
Genes and Alleles: Alleles (uh leelz) are the different forms of a gene. The gene that controls stem height in peas, for example, has
one allele for tall stems and one allele for short stems. Each pea plant inherits two alleles from its parents—one allele from the egg and
the other from the sperm. A pea plant may inherit two alleles for tall stems, two alleles for short stems, or one of each.
2. Each pea plant ___________two____________ from its parents—one allele from the egg and the other from the sperm.
An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are
recessive. A dominant allele is one whose trait always shows up in the organism when the allele is present. A recessive allele, on the
other hand, is hidden whenever the dominant allele is present. A trait controlled by a recessive allele will only show up if the organism
does not have the dominant allele.
3. A _________________ allele is masked (hidden) whenever the dominant allele is present.
A dominant allele is represented by a capital letter. For example, the allele for tall stems is represented by T. A recessive allele is
represented by the lowercase version of the letter. So, the allele for short stems would be represented by t.
1. Which allele is recessive for stem height in the diagram below?
Tall
2. Which symbol (letter) would represent the allele for the tall stem gene (trait)?
3. Which symbol (letter) would represent the allele for the short stem gene (trait)?
4. What is a purebred plant?
T
or
T
or
short
or
t
t
5. In the diagram above place the correct symbols (Ts and/or ts) for the alleles in each plant.
6. Circle the plants above that have a “hidden gene” (or an allele not expressed). There are 4 of them.
1. Where are genes located?_____________________________________________
Mendel’s work showed that genes exist, but he did not know what structures in cells contained
genes. Chromosomes are structures for how offspring have traits similar to those of their
parents. One allele in a pair comes from the organism’s female parent and the other allele
comes from the male parent. These paired alleles are carried on paired chromosomes which is
known as the chromosome theory of inheritance. According to the chromosome theory of inheritance, genes are carried from parents
to their offspring on chromosomes.
2. What is the chromosome theory of inheritance?___________________________________________________________________
Chromosomes are made up of many genes joined together like beads on a string. Each chromosome contains a large number of genes,
each gene controlling a particular trait. Each chromosome pair has the same genes. The genes are lined
up in the same order on both chromosomes.
1. In the chromosome pair circle the dominant A gene. Place an X on the recessive a gene. 
2. How many genes are being masked in the chromosome pair? a. 1 b. 2
c. 3
d. 4
-
Across
3. A table used to show the
possible outcomes of a
genetic cross.
6.Gene are located on ______.
8. An organism that has two different alleles for a trait.
9. The passing of traits from parent to offspring.
10. physical characteristics.
11. The study of heredity
Down
1. Factors that control traits.
2. A different forms of a gene
4. An allele that is masked, in the presence of another gene.
5. An allele whose trait always shows up in an organism.
7. The likely-hood that a particular event will occur.
8. An organism that has two identical alleles for the same trait.
An organism interacts with both the living and nonliving parts of its habitat. The living parts of a habitat are called biotic factors (by
aht ik). Abiotic factors (ay by aht ik) are the nonliving parts of an organism’s habitat. They include water, sunlight, oxygen,
temperature, and soil. All living things require water to carry out their life processes. Sunlight is needed for photosynthesis, sunlight
is an important abiotic factor for most living things. Most living things require oxygen to carry out their life processes. The
temperatures that are typical of an area determine the types of organisms that can live there. Soil type is an abiotic factor. Topsoil is a
mixture of rock fragments, nutrients, air, water, and organic material (decaying remains of living things). However the bacteria that
live in the soil is a biotic factor.
1. Sunlight is a(n) (abiotic/biotic) factor. Bacteria is a(n) (abiotic/biotic) factor. Water is a(n) (abiotic/biotic) factor.
Soil is a(n) (abiotic/biotic) factor. Sunlight is a(n) (abiotic/biotic) factor. Temperature is a(n) (abiotic/biotic) factor.
3. List one abiotic factor that is require for photosynthesis.___________ What does abiotic mean?_________________
When an organism in an ecosystem eats, it obtains energy. The organism uses some of this energy to move, grow,
reproduce, and carry out other life activities. This means that only some of the energy it obtains will be available
to the next organism in the food web. The most energy is available at the producer level of the pyramid. As you
move up the pyramid, each level has less energy available than the level below.
1. Label the Energy Pyramid→. Start with producers, then herbivores and then Carnivores.
2. A food (chain/web) is more realistic. Most producers and consumers are part of many food (chains/webs).
3. ____________ enters most ecosystems as sunlight. The most _____________ is available at the producer level of the
pyramid. There is less __________ available as you move up the pyramid because ___________is used to move & grow.
4. Why is there more energy available at the bottom of the food chain?_______________________________________