Download Given a Punnett square. Analyze a Dihybrid cross

BIOLOGY 1
STANDARD 4.0
LESSON 4.3 and 4.12
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The student will investigate the concepts of genetics and heredity,
different methods of reproduction, patterns of inheritance, and genetic
disorders; as well as, explore and evaluate the DNA technologies from
both a scientific and ethical perspective.
Lesson 7- Determine the genotype and phenotype of a monohybrid cross
Given a Punnett square. Analyze a Dihybrid cross
Complete the following worksheet using the note link below
Punnett Squares
Now that you have gained an understanding of simple genetic principles and how
probability and genetics are related, you are ready to start applying these concepts to
solving simple genetic problems.
A Punnett square is a chart which shows/predicts all possible gene combinations in a
cross of parents (whose genes are known). Punnett squares are named for an English
geneticist, Reginald Punnett. He discovered some basic principles of genetics, including
sex linkage and sex determination.
Use the following two Punnett Square Tutorials to learn how to use Punnett Squares:
"The Punnet Square (in baby steps)".
Punnett Squares Tutorial #1
Punnett Squares Tutorial #2
The Punnett Square:
The Punnett square is a chart, used by geneticists, to help determine the
chances of an offspring receiving a particular characteristic. The Punnett
square will not tell you how many offspring will develop, or the order in which
they will be born. B = brown hair and b = blonde hair.
Example: --------------------------Bb X Bb ----------Parents that are heterozygous
for Brown hair.
Gametes: ------------------------B and b ; B and b-------Each parent produces 2
gametes.
Punnett Square:
Gametes -------|--->
B
b
B
b
--------------------------------- -------------------------------------------
---------------------
1. What are the chances of the offspring being homozygous brown haired?
____________.
2. What are the chances of the offspring having blonde hair?
__________________.
3. What are the chances of the offspring being heterozygous brown haired?
___________.
4. What is the genotypic ratio? _________________.
5. What is the phenotypic ratio? ________________.
6. What is the dominant gene? _________________.
7. Is there a heterozygous blonde haired offspring? ___________. Why?
____________________________________________________________
Questions:
8. If curly hair is dominant to straight hair, what letters will we use to show
these genes?
9. If a heterozygous curly haired male marries a straight haired female, what
would there genotypes look like using the letters in question 8 ?
________________X _________________.
10. What would be the gametes for the male parent?
____________________
11. What would be the gametes for the female parent?
___________________
12. Work out the Punnett square in the space below and answer the
following questions.
Gametes -------|--->
B
b
B
b
--------------------------------- -------------------------------------------
---------------------
13. What are the chances of the offspring being homozygous curly haired?
___________________.
14. What are the chances of the offspring having straight hair?
__________________.
15. What are the chances of the offspring being heterozygous curly haired?
____________.
16. What is the genotypic ratio? _________________.
17. What is the phenotypic ratio? ________________.
18. What is the dominant gene? _________________.
19. Is there a heterozygous straight haired offspring? ___________.
Why?________________________________________________________
20. If yellow pods are dominant to green pods, what letters will we use to
show these genes?
21. If a heterozygous yellow male is crossed with another heterozygous
yellow female, what would there genotypes look like using the letters in
question 20 ?
_____________________________________________________________
22. What would be the gametes for the male parent?
____________________
23. What would be the gametes for the female parent?
___________________
24. Work out the Punnett square in the space below and answer the
following questions.
Gametes -------|--->
B
b
B
b
-------------------------------- -------------------------------------------
---------------------
25. What are the chances of the offspring being homozygous green?
________________.
26. What are the chances of the offspring being yellow?
__________________.
27. What are the chances of the offspring being heterozygous yellow?
________________.
28. What is the genotypic ratio? _________________.
29. What is the phenotypic ratio? ________________.
30. What is the dominant gene? _________________.
31. Is there a heterozygous green offspring? ___________. Why?
__________________
More practice problems
Monohybrid Cross Learn about the basic principles that govern Mendelian inheritance in
plants and animals.
Dihybrid Cross Investigate the principles that govern inheritance of different traits in a
dihybrid cross.