Download Name____________________ Genetics Study Guide/Reality Check

Name____________________
Genetics Study Guide/Reality Check
Part I: Vocabulary—Define the terms below
1. Genetics = The scientific study of heredity.
2. Genes = Factors that control traits; specific sequences of DNA that are the
“blueprint” for building proteins.
3. Heredity = The passing of traits (DNA) from parents to offspring.
4. Heterozygous = A genotype that contains two different alleles for a trait. Example:
Aa, Bb, Cc. These individuals will always show the dominant phenotype.
5. Homozygous = A genotype that contains two identical alleles for a trait. Example AA
or aa, BB or bb
6. Genotype = The genetic “makeup” of an organism. The combination of alleles for a
certain trait.
7. Phenotype = The physical expression of the genotype. The physical appearance of an
organism. What you look like.
8. Alleles = Different forms of a gene for a certain trait. May be dominant or recessive
9. Dominant Allele = The allele that appears if it is present in the genotype.
10. Recessive Allele = The allele that gets “masked” by the dominant allele if both are
present in the genotype (heterozygous). An organism needs two copies of the
recessive allele to show the recessive phenotype.
11. Traits = Physical characteristics. Eye color, toe length, nostril size, nose shape, hair
texture, etc.
12. Punnett Squares = A tool that is used to show all of the possible combinations of
alleles (genotypes) of the offspring of two parents.
13. Chromosome = A tightly compacted form of DNA that contains genetic information
and is passed from parent to offspring
14. Double Helix = The shape of the DNA molecule; looks like a twisted staircase
15. DNA = Deoxyribonucleic acid; chemical “instructions” made up of a sugar and
phosphate backbone and rungs made up of 4 nitrogen bases. The order of the bases
determines the “genetic code”.
16. Purebred = homozygous
17. Hybrid = heterozygous
Part II: Punnett Squares—Set up the crosses and determine the probabilities for the
results.
18. Cross TT x tt. Show the percentages for TT, Tt, tt, homozygous, heterozygous, tall,
short, dominant, and recessive.
T
T
t
Tt
Tt
t
Tt
Tt
TT
Tt
tt
Homozygous
Heterozygous
Tall
Short
Dominant
Recessive
0%
100%
0%
0%
100%
100%
0%
100%
0%
19. Cross Tt x Tt. Show the percentages for TT, Tt, tt, homozygous, heterozygous, tall,
short, dominant, and recessive.
TT
Tt
tt
Homozygous
Heterozygous
Tall
Short
Dominant
Recessive
25%
50%
25%
50%
50%
75%
25%
75%
25%
T
t
T
TT
Tt
t
Tt
tt
20. Cross Tt x tt. Show the percentages for TT, Tt, tt, homozygous, heterozygous, tall,
short, dominant, and recessive.
TT
Tt
tt
Homozygous
Heterozygous
Tall
Short
Dominant
Recessive
0%
50%
50%
50%
50%
50%
50%
50%
50%
T
t
t
Tt
tt
t
Tt
tt
21. Green tails (G) are codominant with blue tails (B). Cross BG x BG. What are the possible
phenotypes for the offspring? If there were 100 offspring, how many would you expect to
have of each phenotype?
GG
25%
GB
50%
BB
25%
Homozygous
50%
Heterozygous
50%
Blue
25%
Green
25%
Blue-Green
50%
B
G
B
BB
BG
G
BG
GG
21. Smelly breath (Q) is incompletely dominant with non-smelly breath (Q’) Cross QQ’ x
QQ’. List the possible genotypes and phenotypes of the offspring. What is the
percent chance of each?
QQ
QQ’
Q’Q’
Homozygous
Heterozygous
Smelly
Average
Non-smelly
25%
50%
25%
50%
50%
25%
50%
25%
Q
Q’
Q
QQ
QQ’
Q’
QQ’
Q’Q’
Spongebob #7
No, it is not possible. Stubby nose is the recessive trait, therefore an individual needs
two copies of the recessive allele. If both parents have the recessive trait that means
their genotype is nn. Since there is no N to pass on, none of the offspring will have a
regular nose.
n
n
n
nn
nn
n
nn
nn
Spongebob #8
She would have to marry someone with a homozygous long nose. Since the only allele that
he could pass on is an “N” all of the offspring would have long noses.
N
N
n
Nn
Nn
n
Nn
Nn
Part III: Short Answers
22. Describe the shape of a DNA molecule and list the bases that make up the chemical
code. The shape of the DNA molecule is a double helix or twisted ladder. The four
bases of DNA are A, T, C, and G. (Adenine, Thymine, Adenine, and Guanine)
23. What are the chemical molecules that make up the backbone of the DNA molecule?
The chemical molecules are sugar (deoxyribose) and phosphate.
24. What is a mutation? _A mutation is a change in a gene or DNA sequence (sentence).
25. What is the base-pairing rule? _A with T, C with
G_______________________________________________________________
________________________________________________________________
26. Complete the complementary sequence of the DNA molecule below:
A T C G G G C C T T A C C T
T A G C C C G G A A T G G A
27. Who was Gregor Mendel and what did he do for the study of heredity? Gregor
Mendel was an Austrian monk who observed that offspring sometimes looked
different than their parents. This led to his hypothesis that certain traits are
dominant and some are recessive.
28. Explain the experiments of Gregor Mendel. Be sure to include information about what
traits he looked at, why he used pea plants, and what “P” generation, “F1” generation,
and “F2” generation mean. He first took a purebred tall and purebred short plant.
All of the F1 generation was tall. Then, he took two F1 plants and crossed them
together. The F2 generation had ¾ tall plants and ¼ short plants.
29. What phenotype (dominant or recessive) do all heterozygous individuals show? Why?
_Dominant because all heterozygous organisms have a copy of each allele; dominant
and recessive. Since the organism has a copy of the dominant allele, the individual will
show the dominant trait.
30. How is probability related to genetics? Use examples to explain. Genetics is based
on the fact that there is a certain chance that one sex cell will be selected over
any other. Those sex cells contain the chromosome that determine traits. In
punnett squares there are four possible outcomes or combination of alleles. The
punnett square does not tell us what will happen, but rather tells us what the
probability of a certain genotype in the offspring.
Draw a pedigree for the family described below. Use shading to show individuals with
straight hair.
a. Mom (Angela) has curly hair.
b. Dad (Thomas) has straight hair.
c. The three children are Carly, Michael, and Frank
d. Frank is the oldest; he has curly hair. Michael has curly hair, too.
e. Carly is the youngest. She has strait hair.
Some clues for setting up pedigrees:
Symbol for females = _circle____
Symbol for males = ___square____
Oldest child starts on the _left____ side
Angela
Frank
Thomas
Michael
Carly