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1) What is a locus?

1. A locus is the location of an allele on a chromosome


2) Approximately how many genes do humans possess?

2. 21,500


3) What is each version of a gene called?

3. allele


4) What is the condition referred to if two copies of a gene are identical alleles?

4. homozygous


5) What is the condition referred to if two copies of a gene are different alleles?

5. heterozygous


6) What is an allele called when that allele's effect on a trait masks that of an allele paired with it?

6. dominant


7) When an allele's effect on a trait is masked by that of an allele paired with it, what is the second allele referred to as?

7. recessive


8) What is the genotype AA referred to as?

8. homozygous dominant


9) What is the genotype aa referred to as?

9. homozygous recessive


10) What is the genotype Aa referred to as?

10. heterozygous


11) What are the alleles an individual inherits called?

11. genotype


12) What are observable functional or physical traits called?

12. Phenotype


13) What is the most accurate description of an organism with genotype AaBb ?

13. Dihybrid


14) Gene A occurs on chromosome 5, gene B is on chromosome 21. Therefore, these two parts of the chromosomes can NOT be

14. Linked


15) If two parent organisms have different alleles for a gene that an experimenter wants to test, what test will he or she perform?

15. Test cross


16) What gametes will a parent with the genotype CC will produce?

16. C


17) When homologues separate into different gametes after meiosis I, the genes of each pair separate as well. What is this principle called?

17. Segregation


18) The principle of segregation applies most specifically to events occurring in preparation of what?

18. gametes


19) What does the theory of segregation deal with?

19. explains the behavior of a pair of alleles during meiosis.


20) If R is dominant to r, the offspring of the cross of RR with rr will have what phenotype?

20. the same phenotype as the RR parent


21) If tall (D) is dominant to dwarf (d), and two homozygous varieties DD and dd are crossed, then what phenotypes of offspring will be produced?

21. all tall


22) If all offspring of a cross have the genotype Aa, what would the parents of the crosses most likely be?

22. AA x aa


23) What is a graphic tool used to determine the probable outcome of genetic crosses called?

23. Punnett square


24) When the first generation parents are homozygous for different alleles, a 3:1 phenotype ratio will most likely appear in which generation of offspring?

24. F2


25) In a monohybrid cross, what kind of genes "disappear" in the F1 generation?

25. recessive


26) What is the F2 phenotypic ratio of a monohybrid cross?

26. 3:1


27) In the cross Cc x Cc, gametes have a ____ chance of receiving either allele.

27. 50 x 50


28) In a Punnett square, what do the letters within the little boxes represent?

28. offspring genotypes


29) If short hair (L) is dominant to long hair (l), then to determine the genotype of a short-haired animal it should be crossed with what genotype animal?

29. ll


30) When an individual with an unknown genotype is crossed with an individual that is homozygous recessive for the trait being studied, what is the procedure called?

30. testcross