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College Biology

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1. An organism that is true breeding for a trait is said to be (a) homozygous (b) heterozygous (c) a monohybrid (d) a dihybrid

2. At the end of meiosis, how many haploid cells have been formed from the original cell? (a) one (b) two (c) three (d) four

3. When Mendel transferred pollen from one pea plant to another, he was ___ the plants. (a) self pollinating (b) cross pollinating (c) self fertilizing (d) cross fertilizing

4. A short pea plant is
(a) homozygous recessive (b) homozygous dominant (c) heterozygous (d) a dihybrid

5. Which describes a dominant trait in garden peas?
(a) wrinkled, yellow peas (b) inflated, yellow pods (c) round green peas (d) purple, axial flowers

6. During what phase of meiosis do homologous chromosomes cross over? (a) prophase I (b) anaphase I (c) telophase I (d) telophase II

7. Recessive traits appear only when an organism is (a) mature (b) different from its parents (c) heterozygous (d) homozygous

8. Mendel’s use of peas was a good choice for genetic study because (a) they produce many offspring (b) they are easy to grow (c) they can be self-pollinating (d) all of these

9. A dihybrid cross between two heterozygous parents produces a phenotypic ratio of (a) 3:1 (b) 1:2:1 (c) 9:3:3:1 (d) 1:6:9

10. If two heterozygous organisms for a single dominant trait mate, the ratio
of their offspring should be about ________3:1____________________________.

11. A trait that is hidden in the heterozygous condition is said to be a _________recessive________________ trait.

12. An organism that has two different alleles for a trait is called ___heterozygous__________________.

13. The process that results in Down syndrome is called ________nondisjunction______.

14. If a species normally has 46 chromosomes, the cells it produces by meiosis will each have _________23_________________ chromosomes.

15. Metaphase I of meiosis occurs when _______homologous chromosomes__________ line up next to each other at the cell’s equator.

16. In the first generation of Mendel’s experiments with a single trait, the _____recessive______ trait disappeared, only to reappear in the next generation.

17. A cell that has successfully completed meiosis has a chromosome number called ______happloid____________.

18. Meiosis results in the direct production of _______gametes____________.

Essay type questions

19. Why do you think Mendel’s results are also valid for humans?

Like plants humans reproduce sexually, have chromosomes and genes and have traits controlled by genes

20. On the average, each human has about six recessive alleles that would be lethal if expressed. Why do you think that human cultures have laws against marriage between close relatives?

The likelihood of close relatives sharing the same recessive alleles is greater than in the general population, raising the risks that a child would be homozygous recessive for a trait.

21. Assume that a couple has four children who are all boys. What are the chances their next child will also be a boy? Explain your answer.

50% because previous births do not affect any children that will follow.

22. How does separation of homologous chromosomes during anaphase I of meiosis increase variation among offspring?

The order of lining up at the equator during metaphase 1

23. Relating to the methods of science, why do you think it was important for Mendel to study only one trait at a time during his experiments?

Controlled experiments require that no more than one variable be changed or tested at a time. If Mendel changed or checked more than one variable at a time he would not have known what caused the changes.

24. Why is it sometimes impossible to determine the genotype of an organism that has a dominant phenotype? Dominant genes completely mask the recessive ones, and you can not tell if the organism is heterozygous or homozygous dominant.

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