GENETICS REVIEW SHEET ANSWER KEY
NAME___________________________
Use your notes, text, and other resources to answer the following questions.
1.
What happens to the DNA in your cells when they divide by mitosis? Every chromosome is copied exactly
2.
3.
How do the 4 bases below combine to form the “rungs” in a DNA molecule?
Adenine-guanine-cytosine-thymine
Adenine pairs with thymine; guanine pairs with cytosine held together by hydrogen bonds
4.
How does DNA relate to chromosomes? The chromosome is made up of DNA tightly coiled around histone and
nonhistone proteins
5.
Compare the cells that are formed in mitosis to their parent cells. Offspring are genetically identical to the parent cell
6.
Compare the cells that are formed in meiosis to their parent cells. They contain half the number of chromosomes
7.
How does a gene relate to DNA? A gene is a segment of DNA on a chromosome
8.
What does a gene do in an organism? Each gene directs the expression of a specific trait
9.
How many chromosomes are in a human body cell? How many in a sex cell? 46 in a body cell, 23 in a sex cell
10. Do organisms that are less complex than humans have to have less chromosomes? Not necessarily; sometimes they even
have more
11. What is another name for a sex cell (NOT egg or sperm)? Gamete or germ cell
12. Who was Gregor Mendel? An Austrian monk; considered to be the father of modern genetics because of his work with
pea plants, and the discovery of dominant and recessive traits, and independent assortment of traits during gamete
production
13. How did Mendel develop a pure strain of pea plants for a specific trait such as height or seed color? Bred several different
strains of plants over many generations using both self-pollination and cross-pollination
14. How did Mendel cross these plants that had different traits? What is the name of this process? He used a paint brush to
take pollen from the male parts of one plant and putting them into the female parts of another; this is cross-pollination
15. What did Mendel call these types of traits that the plants had for height and color and so on? Dominant or recessive,
depending on whether or not they masked the other form of the trait (e.g., yellow seeds that he knew carried the green
trait)
16. Mendel crossed literally thousands of plants for any given trait. Why was this important for his results? Verification of
results are critical in every experiment, so that the result obtained cannot be attributed to chance. This is why
experiments must also be able to replicated exactly
17. Describe incomplete dominance. Give an example. Incomplete dominance results in a third phenotype that is between
both heterozygote extremes, such as in some flowers: RR = red, RW = pink, and WW = white, or with black, gray and
white rabbits
18. Describe a sex-linked trait. Give an example. Sex-linked traits are on the sex chromosomes, usually the X chromosome.
Hemophilia, baldness, colorblindness are all sex-linked traits
19. What is any sudden genetic change in an organism called? mutation
20. List 5 possible mutagens. Radiation, some viruses, chemicals, tar, smoke, smog, ultraviolet light
21. What is most often the cause of a mutation? A point mutation
22. What general type of mutation is albinism? Down syndrome? Albinism is an autosomal recessive trait (not on the X
chromosome), Down’s syndrome is chromosomal (too many chromosomes)
23. How does a cell normally make what a gene is coding for? Genes direct protein synthesis to produce a specific trait
24. What is it called when one base is missing in a gene that contains hundreds of bases? Point mutation
25. What general type of mutation has the most drastic effect? Why? Chromosomal mutations, because each chromosome
carries many genes
26. Briefly describe the following types of mutations:
a)
Nondisjunction—chromosomes fail to separate properly during meiosis
b) Polyploidy—a higher than normal number of chromosomes, as in some plants that have 3n, 4n or even a higher
number of chromosomes, resulting in a larger plant
c)
Germ mutation—mutations in reproductive cells that may be passed on to offspring
d) Somatic mutation—mutations (often caused by mutagens) in body cells, which affects the individuals but can’t be
passed on to offspring
e)
PKU—a gene mutations resulting in a person’s inability to break down phenylalanine
f)
Sickle-cell anemia—results in sickle-shaped red blood cells; they lose ability to effectively carry oxygen
g)
Down syndrome—trisomy-21, caused by nondisjunction
h) Turner’s syndrome—a monosomy, missing an X chromosome
i)
Klinefelter’s syndrome—another trisomy, XXY
27. Describe what happens with multiple alleles and list two human traits that are coded for by multiple alleles. Traits with
many phenotypes such as blood type, height, skin tone, hair and eye color, may be controlled by more than one allele,
since the genes are CODOMINANT, and are both fully expressed in the phenotype