2. Which hereditary rule explains why a self-fertilizing parent that is heterozygous for the A locus (Aa) can produce offspring that are AA or aa?

Transcription

1 Heredity 1. Technology Enhanced Questions are not available in Word format. 2. Which hereditary rule explains why a self-fertilizing parent that is heterozygous for the A locus (Aa) can produce offspring that are AA or aa? A. dominance B. principle of segregation C. codominance D. principle of independent assortment 3. One possible form of a gene that codes for a particular trait is known as. A. a chromosome B. a genotype C. an allele D. a phenotype 4. Trey goes to a rabbit farm to look at a litter of newborn rabbits. The newborns are all different colors. They are gray, black, white, light brown, and dark brown. What type of inheritance pattern are these rabbits likely displaying? A. dominant-recessive B. codominance C. incomplete dominance D. multiple alleles

2 5. Carla receives an allele for blue eyes from her mother, and an allele for brown eyes from her father. If brown eye color is a dominant trait and blue eye color is a recessive trait, what can be determined about the color of Carla's eyes? A. Carla has brown eyes. B. Carla's eye color can not be determined. C. Carla has green eyes. D. Carla has blue eyes. 6. Punnett squares depict the genotypes of two parents and are used to predict the inherited traits of offspring. Which of the following would be the missing predicted trait in the table below? A. AO B. OO C. AA D. OA 7. A student crosses two pea plants. One is homozygous dominant for axial flowers, and the other is heterozygous for axial flowers. If the student examines 200 offspring pea plants, which of the following is a reasonable result? A. 149 with axial flowers, 51 with terminal flowers B. 47 with axial flowers, 153 with terminal flowers C. 200 with axial flowers, 0 with terminal flowers D. 98 with axial flowers, 102 with terminal flowers

3 8. Sarah is doing an experiment on pea plants. She is studying the color of the pea plants. Sarah has noticed that many pea plants have purple flowers and many have white flowers. Sarah crosses a homozygous white flower and a homozygous purple flower. The cross results in all purple flowers. What is true of the color of pea plants? A. White flowers and purple flowers are codominant. B. Purple flowers are dominant to white flowers. C. Purple flowers and white flowers are recessive to red. D. White flowers are dominant to purple flowers. 9. Fifty percent of the offspring produced by a cross between pea plants have seeds with a wrinkled (r) appearance caused by the presence of a homozygous recessive gene. What were the genotypes of the parents? A. RR Rr B. RR rr C. Rr Rr D. Rr rr 10. Technology Enhanced Questions are not available in Word format. 11. Technology Enhanced Questions are not available in Word format.

4 12. After crossing-over as shown below, what would the sequence of genes be for each of the chromatids? A. ABCD, abcd, ABcd, abcd B. ABab, CDCd, abab, CDcD C. ABCD, abcd, abcd, abcd D. ABCd, abcd, abcd, abcd 13. Gregor Mendel developed several laws of heredity over the course of his genetic research. What does the first law of heredity, the law of segregation, state about genes? A. Mutations can only occur in heterozygous organisms. B. Dominant alleles are always more likely to be inherited. C. Two alleles for a trait separate when gametes are formed. D. Alleles of different genes separate independently of one another during gamete formation. 14. It is possible for an organism to inherit a gene with two dominant alleles. What is a gene with two dominant alleles that are expressed at the same time? A. polygenic inheritance B. heterozygous C. incompletely dominant D. codominant

5 15. A certain type of flower has two alleles for color (blue, purple), and two alleles for stem height (tall, short). A tall blue flower and a short purple flower are crossed, resulting in tall blue flowers, short blue flowers, tall purple flowers, and short purple flowers. What law does this example help to prove? A. Law of Multiple Alleles B. Law of Genetic Inheritance C. Law of Segregation D. Law of Independent Assortment 16. Human height is a polygenic trait. This means that the A. trait is controlled by the genes inherited from the father only. B. trait is controlled by the genes inherited from the mother only. C. trait is controlled by more than one pair of genes. D. trait is completely controlled by only one pair of genes. 17. A(n) is a characteristic arising from genes located on gender-determining chromosomes. A. allele B. genotype C. autosomal trait D. sex-linked trait 18. Mrs. Smith has blood type A. Her father has blood type A, and her mother has blood type B. If Mr. Smith has blood type AB, what is the probability that they will have a child with blood type AB? A. 50% B. 100% C. 25% D. 0% 19. A student crosses two true-breeding pea plants, one with green pods and the other with yellow pods. If yellow is dominant over green, what phenotypic results will the student find in the F1 generation? A. 100% yellow B. 75% green, 25% yellow C. 75% yellow, 25% green D. 100% green 20. In pea plants, tall (T) plants are dominant over short (t) plants. If a heterozygous (Tt) pea plant is crossed with a homozygous dominant (TT) pea plant, all of the resulting pea plants should be tall (TT or Tt). Each plant

6 will receive a dominant allele from the homozygous dominant plant, while they could receive either a dominant or recessive allele from the heterozygous plant. The fact that each plant gets only one allele from each parent plant is detailed in the Law of. A. Segregation B. Multiple Alleles C. Genetic Inheritance D. Independent Assortment 21. What is the term used to describe the heritable, physical characteristics of a living organism? A. allele B. pedigree C. phenotype D. genotype

7 22. According to Mendel's Law of Segregation, meiosis involves the separation of a parent organism's alleles in order to form gametes. Since the alleles separate into different gametes, only one allele passes from each parent on to an offspring. This segregation of alleles during meiosis decreases the genetic variability of the offspring. A. increases the genetic variability of the offspring. B. decreases the chance that an offspring will receive a dominant allele. C. increases the chance that an offspring will receive a dominant allele. D. 23. A cross between two squash plants that produce yellow squash results in 124 offspring: 93 produce yellow squash and 31 produce green squash. What are the likely genotypes of the plants that were crossed? A. both YY B. both yy C. one YY, one Yy D. both Yy 24. Guinea pig coat color is determined by a single gene. The allele for black coat color is dominant to brown. In a cross between two black-haired guinea pigs, 20 offspring are born. If both parents were heterozygous, probability would predict that approximately how many of the 20 offspring would have brown hair? A. 0 B. 15 C. 5 D. 10

8 25. An organism's genotype can best be defined as its A. inherited physical appearance. B. number of chromosomal pairs. C. inherited combination of alleles. D. number of recessive genes. 26. AB blood type is an example of. A. polygenic inheritance B. independent assortment C. incomplete dominance D. codominance 27. A recessive gene located on the X chromosome is the cause of color blindness in affected individuals. Males are more likely to be colorblind than females because A. males have two copies of the X chromosome. B. females have no copies of the X chromosome. C. color blindness is associated with high testosterone levels. D. males have only one copy of the X chromosome. 28. Lisa breeds snakes. She bred a solid brown male python with a tan female python whose body was covered with a black diamond pattern. Upon hatching, all of the baby pythons were brown with a faint diamond pattern. Which of the following inheritance patterns most likely determined the color of Lisa's baby pythons? A. autosomal dominant-recessive B. codominance C. incomplete dominance D. sex-linked 29. Lupe grows pea plants in her garden. The pea plants have flowers that can be either purple or white, with purple color being dominant to white color. The peas produced by Lupe's pea plants can also be either round or wrinkled, with round peas being dominant to wrinkled peas. Lupe crosses two pea plants that are heterozygous for both traits. If a gamete from this cross receives a dominant allele for flower color, how does this influence the probability of the gamete receiving a dominant allele for pea shape? (Assume that the genes for flower color and pea shape follow the law of independent assortment.)

9 It has no effect on the probability of the gamete receiving a dominant allele for pea shape. A. It increases the probability that the gamete will receive a dominant allele for pea shape. B. It decreases the probability that the gamete will receive a dominant allele for pea shape. C. It causes the gamete to be unable to receive a dominant allele for pea shape. D. 30. Which of the following describes an allele whose characteristic phenotype is masked by the presence of a second, different allele? A. dominant B. recessive C. polygenic D. codominant Answers B 3. C 4. D 5. A 6. B 7. C 8. B 9. D C 13. C 14. D 15. D 16. C 17. D 18. C 19. A 20. A 21. C 22. B 23. D 24. C 25. C 26. D 27. D 28. C 29. A 30. B Explanations

10 The principle of segregation states that the two alleles present in the reproductive organs of an organism will be separated, or segregated, into different cells as the gametes (sex cells) form. As a result, each sex cell will only contain one allele for each gene locus. These segregated alleles can then combine with a gamete of the opposite sex type, allowing one allele from each parental gamete to combine to form the offspring. So, if this heterozygous parent (Aa) combines with a homozygous dominant parent (AA), there is a 50% chance that a homozygous dominant offspring (AA) is produced. If it combines with a homozygous recessive parent (aa), there is a 50% chance that a homozygous recessive offspring is produced (aa). If the heterozygous parent combines with another heterozygous parent, there is a 25% chance of producing a homozygous dominant offspring, and a 25% chance of producing a homozygous recessive offspring. 3. An allele is one possible form of a gene that codes for a particular trait. Humans have two alleles for most traits. These alleles can be dominant or recessive. Dominant alleles are always expressed in the phenotype of an organism that has either one or two copies of the allele. Recessive alleles are expressed only if an organism has two copies of the recessive allele. 4. Since the rabbits display more than two colors (and more than just variations of a color), it is likely that the rabbits' pattern of inheritance involves multiple alleles. Rabbits actually have four alleles, of which dark gray (black) is dominant to all other alleles and solid white is recessive. 5. Carla is heterozygous for the trait of eye color. She has one gene for blue eyes, and one for brown eyes. Since the gene that codes for brown eye color is dominant, the trait for this eye color will be expressed, and Carla will have brown eyes. 6. Each square represents a segregated outcome. The missing square is a cross between O and O and could only produce OO, which would be known as simply O. 7. A Punnett square is a diagram used by biologists to determine the probability of an offspring having a particular genotype. In a Punnett square, the parental genotypes are written on the outside of the squares and the products are written inside the squares (much like a multiplication table). The Punnett square for a cross between a homozygous dominant pea plant and a heterozygous pea plant appears below. Since all of the offspring possess at least one dominant allele (A), the expected result would be 100% axial flowers (50% homozygous dominant (AA), 50% heterozygous (Aa)). 8. If all of the offspring of a homozygous white flowered pea plant and a homozygous purple flowered pea plant have purple flowers, this means that purple flowers are dominant to white flowers. If white flowers were dominant, all of the offspring would have white flowers.

11 9. To produce 50% homozygous recessive plants, one of the parents must have contributed 100% of the recessive alleles to the cross; one parent must have the genotype rr. The other parent must have had one recessive allele and one dominant allele to produce 50% of each characteristic when paired with the recessive alleles from the homozygous recessive parent; this parent must have the genotype Rr Crossing-over is a process that occurs in prophase I of meiosis in which portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid portions of the other homologous chromosome. The corresponding chromatid portion in this case is the crossing portion of the Dd allele. 13. The law of segregation describes the behavior of chromosomes during meiosis. Specifically, the law of segregation says that two alleles representing the same trait will always separate during meiosis so that each gamete will only have one copy of the allele for that trait. In another law, the law of independent assortment, Mendel states that the inheritance of one trait will not affect the inheritance of another trait. In other words, the genes of an organism sort independent of one another in the gametes (e.g., there is no relationship in inheritance between the color of a pea plant and its' height). 14. Codominance occurs when two dominant alleles are expressed at the same time. Incomplete dominance occurs when an individual displays a phenotype that is intermediate between the two parents. Polygenic inheritance occurs when several genes influence a trait. Heterozygous is the term describing an individual with two different alleles present for the same trait. 15. The fact that the cross of a tall blue flower and a short purple flower leads to four varieties of flowers is an example of the Law of Independent Assortment. Since each allele and trait are sorted independently of each other, any combination of traits and alleles is possible. 16. Polygenic traits are traits that are controlled by more than one pair of genes, so multiple independent pairs of genes have similar effects on the same trait. Human height, body form, and skin color are examples of polygenic traits.

12 17. In humans, gender is determined by the number of X chromosomes. Females have two X chromosomes, and males have one X and one Y chromosome. A sex-linked trait is a physical or biochemical characteristic arising from genes located on gender-determining (X and Y) chromosomes. 18. Typically, there are two alleles for a trait a dominant trait and a recessive trait. The blood type trait, however, has three alleles, which correspond to the blood types A, B, and O. The A and B alleles are dominant to the O allele, but they do not show dominance over each other. The result is that if a person has an A allele and a B allele, he or she will have type AB blood. Mrs. Smith's parents have blood types A and B. Since Mrs. Smith has blood type A, it logically follows that she must carry one A allele and one recessive antigen-free O allele obtained from her mother, who has type B blood. (If her parents had both been homozygous for their blood types, Mrs. Smith could only have had AB blood. Her mom must have been heterozygous (BO) for her blood type in order for Mrs. Smith to have blood type A.) So, if Mrs. Smith's blood type (AO) is crossed with Mr. Smith's blood type (AB), their offspring will have a 50% chance of being blood type A (includes AA and AO), a 25% chance of being blood type AB, and a 25% chance of being blood type B (BO only). 19. True-breeding plants are those that produce offspring with the same phenotype as the parents when selffertilized. This means that the parents must have been homozygous for the trait under study. Whether the green versus yellow pods are controlled by one gene locus or multiple ones, the F1 generation of a cross between homozygous dominant and homozygous recessive parents will always resemble the dominant parent trait. Thus, the F1 generation of this cross will result in 100% yellow offspring. 20. The fact that each plant gets only one allele from each parent plant is detailed in the Law of Segregation. In normal body cells there are two copies of each chromosome. Each chromosome has its own copy of an allele, so in a body cell, two different alleles can be present for one trait. However, in gametes, there is only one copy of each chromosome and one allele present. Thus, each new organism receives only one allele from each parent. 21. The phenotype of an organism refers to the heritable traits, or characteristics, that are exhibited by that organism. Each specific phenotypic trait can be controlled by one gene, multiple genes, or a combination of genes and environmental influences. 22. The Law of Segregation states that different alleles for the same trait separate when gametes are formed. Since the alleles separate into different gametes, an offspring could receive a gamete with one allele or the other. Thus, a mother that is heterozygous for brown eyes (Bb) could pass either a dominant brown allele (B) or a recessive blue allele (b) for eye color to her offspring. One allele is no more likely than the other to be passed from parent to offspring. The segregation of alleles during meiosis increases the genetic variability of the offspring.

13 23. The genotypes of the plants that were crossed must both have been Yy. A cross between two Yy parents would result in approximately 1/2 Yy offspring, 1/4 YY offspring, & 1/4 yy offspring. Of those offspring, approximately 3/4 (YY and Yy) would express the dominant phenotype. The other 1/4 (yy) would express the recessive phenotype (yy). This is consistent with the results given for the cross. A cross between two YY parents would result in 100% YY offspring that expressed the dominant phenotype. Likewise, a cross between a YY parent and a yy parent would result in 100% Yy offspring that also expressed the dominant phenotype. A cross between two yy parents would result in 100% yy offspring that expressed the recessive phenotype. 24. A cross between heterozygous parents would produce ratios of approximately 1 / 4 homozygous dominant (black hair), 1 / 2 heterozygous (black hair) and 1 / 4 homozygous recessive (brown hair). This predicts about 3 / 4 of the offspring would have black hair and 1 / 4 would have brown hair. It is important to remember that probability is not certain, so it would not be unusual to find actual results that vary wildly from predicted numbers, especially in small offspring sizes. 25. The genotype of an organism can be defined as its inherited combination of alleles. The phenotype of an organism, on the other hand, is its inherited physical appearance. 26. AB blood type is an example of codominance. Codominance is the condition in which a heterozygous individual expresses the phenotype of two alleles. This happens when neither allele is recessive. 27. There are many genetic disorders such as color blindness, hemophilia, and muscular dystrophy that are associated with recessive alleles on the X chromosome. While many females may carry the defective genes, males have the disorders much more often than females. This is because males have only one copy of the X chromosome and females have two copies. If a female is heterozygous (Rr) for hemophilia, she will be a carrier, but will not have the disease because the defective gene is recessive. If a male has the gene for hemophilia, however, he will have the disease because he has no functional copy of the gene to make up for the defective one. 28. The color of Lisa's baby pythons is a result of incomplete dominance. Incomplete dominance results when one allele of a gene is not completely dominant over the other. Instead, both alleles are expressed to some degree, producing a phenotype that appears as a blend of the two possible homozygous phenotypes. Incomplete dominance is distinct from codominance. If the baby pythons in this example had inherited codominant alleles, parts of their bodies would be fully brown, while other parts would be fully tan with a black diamond pattern. 29. The law of independent assortment states that the inheritance of one trait will not affect the inheritance of another trait. In other words, alleles assort independently of one another during gamete formation. If genes follow the law of independent assortment, this means that receiving a dominant allele for one trait does not have any influence on the probability of the gamete receiving a dominant allele for another trait. In Lupe's cross, if a gamete receives a dominant allele for flower color, this has no effect on the probability of the gamete receiving a dominant allele for pea shape.

14 30. An allele whose phenotype cannot be seen when an alternate allele is present on the other chromosome is said to be recessive, because its phenotype is hidden, or dominated, by the other allele. Recessive alleles are usually designated by lower case letters to indicate that they recede in the presence of a dominant allele.