Genetics - Heredity Unit 4 – Overview
Schedule – November 26th through January 8th ; Unit Exam Wednesday, January 17th.
4. Genetics (3rd Six Weeks) Heredity
a) Students will identify and illustrate changes in DNA and evaluate the significance of these changes TEK 6E
b) Students will predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses, and non-Mendelian inheritance. TEK 6F
c) Students will describe how techniques such as DNA fingerprinting, genetic modification, and chromosomal analysis are used to study the genomes of organisms. TEK 6H
Note: The abbreviation TEK stands for Texas Essential Knowledge & Skills Standards referenced below.
Texas Standards Genetics
2. Mutation and sexual reproduction lead to genetic variation in a population. As a
basis for understanding this concept:
a. Students know meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type.
b. Students know only certain cells in a multicellular organism undergo meiosis.
c. Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete.
d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).
e. Students know why approximately half of an individual's DNA sequence comes from each parent.
f. Students know the role of chromosomes in determining an individual's sex.
g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents.
3. A multicellular organism develops from a single zygote, and its phenotype depends on its genotype, which is established at fertilization. As a basis for understanding this concept:
a. Students know how to predict the probable outcome of phenotypes in a genetic cross from the genotypes of the parents and mode of inheritance (autosomal or X-linked, dominant or recessive).
b. Students know the genetic basis for Mendel's laws of segregation and independent assortment.
Textbook – Chapters 9 (pg 242 – 265) 10 (pg 266-293) and 11 (pg 294-323).
Tentative Schedule
Week 1: 11/26 – 11/30 – Chapter ____ - Mutations in DNA & Introduction to Mendelian Genetics
Week 2: 12/3 - 12/7 – Chapter ____ ; Monohybrid Cross + Dihybrid Cross, Pedigrees
Week 3: 12/10 - 12/14 – Chapter ____; Sex-linked traits, Review for CCA Exam, Exam, Karyotype
Week 4: 12/16 - 12/21 – Chapter ____: Genetic Engineering, Classification
Week 5: 1/7 - 1/11 –3rd Review for 3rd Six Weeks Exam, Exam
Week 6: 1/13 – 1/17- Review for EOC Benchmark
Cells reproduce in two ways: 1) mitosis which produces cells that are an exact copy – with complete genetic information, and 2) meiosis which produces cells that have ½ the genetic information of the original cells. Mitosis is a form of asexual reproduction which occurs in general body or somatic cells. Meiosis is the first step of sexual reproduction and occurs only in specific cells called gametes which in males are sperm cells and in females are egg cells or ovules. For example, in humans we have 46 chromosomes (diploid) in our body or somatic cells, but gamete cells only contain ½ or 23 chromosomes each (haploid). The fusion of gametes during sexual reproduction is called fertilization forming a fertilized ovule or zygote. This zygote contains genetic information, ½ from the mother and ½ from the father. We are not exactly like mom or dad but are a variation of them. Thusly, sexual reproduction leads to greater genetic variation. The zygote produced develops into an embryo, then a fetus, and ultimately an offspring representing the union of parental DNA.
The process of meiosis is shown in the adjacent figure. This figure shows the parent cell which itself is a mixture of maternal (mom) and paternal (dad) chromosomes – homologous chromosomes that are two different copies of the same chromosome that diploid organisms (like humans) inherit, one from each parent. These chromosomes are copied once producing sister chromatids that are identical copies of a chromosome. Chromosomes copied are then segregated twice to produce four daughter cells each with one homologous chromosome (haploid). Notice how during metaphase 1 that some pieces of chromosomes move, this is called crossing over and leads to genetic recombination. If the segregations do not happen correctly, like when sister chromatids do not separate, nondisjunction can occur. For example, one of the gametes may have three of one kind of chromosome (trisomy) or only one chromosome (monosomy) resulting in a genetic disorder. One such disorder is Down’s Syndrome aka trisomy 21 because there are 3 copies of chromosome 21.
Of the 46 human chromosomes there are two homologous sex chromosomes and 44 homologous autosomal chromosomes (22 pairs called autosomes). These sex chromosomes determine the sex/gender of the human. If a human has two XX chromosomes female characteristics will be exhibited. If a human has one X and one Y chromosome male characteristics will be exhibited. The genes for traits other than gender on the sex chromosomes have a special pattern of inheritance called sex-linked.
Traits have observable phenotypes and unobservable genotypes (the kinds of genes). Recall that genes are segments of DNA that code for a particular trait (polypeptide). Since we get ½ genetic material from mom and ½ from dad, it is said that we have two alleles for each gene. Certain alleles that are dominant are expressed/exhibited even if only one dominant allele is present. There are also recessive alleles which require two being present before the recessive trait is exhibited. A person with two of the same alleles is termed homozygous and a person with one dominant and one recessive allele is termed heterozygous (hybrid).
The simplest case of phenotype/genotype relations occurs when there is complete dominance - there is no observable effect due to the recessive allele if a dominant allele is present. But there are other possible interactions, incomplete dominance and codominance. With incomplete dominance, the recessive allele contributes to the phenotype even when there is a dominant allele present, such as with pink snapdragons (Rr) when a red snapdragon (RR) is crossed with a white snapdragon (rr). Codominance occurs when both alleles are fully expressed such as with blood type where O is recessive, and A and B are dominant. Such that there can be individuals with types: O blood (oo), A blood (AA or Ao), B blood (Bo or BB), or AB blood (AB). Similar variations are observed in rabbit coat colors.
Predicting the observed phenotype in offspring was first systematically attempted by Gregor Mendel in the late 1880s. A Catholic priest, he studied pea plants very carefully and was able to make some very important observations of inheritance. He manipulated pollination to control his experiments. Using monohybrid crosses Aa x Aa, he showed the Law of Segregation which states that the two alleles for each trait separate during meiosis, then during fertilization two alleles for that trait are restored with phenotypic ratios of 3:1 observed. Next he used dihybrid crosses (AaBb x AaBb) to calculate phenotypic ratios of 9:3:3:1 and interpreting these data he formulated his second law: the Law of Independent Assortment. This law states that allele pairs separate independently during the formation of gametes. Therefore, traits are transmitted to offspring independently of one another. Reginald Punnett used Mendel’s data to develop Punnett Squares that are used to predict the probability of various offspring genotypes and phenotypes. Pedigrees are also genetics maps.

1. Allele__________________________________________________________________
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2. Asexual reproduction______________________________________________________
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3. Autosomal______________________________________________________________
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4. Birth defect_____________________________________________________________
5. Chromosome_____________________________________________________________
6. Co-dominance____________________________________________________________
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7. Cross _________________________________________________________________
8. Crossing over ___________________________________________________________
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9. Dihybrid ______________________________________________________________
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10. Diploid ________________________________________________________________
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11. Dominant _______________________________________________________________
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12. Egg___________________________________________________________________
13. Embryo________________________________________________________________
14. Enzyme________________________________________________________________
15. Fertilization_____________________________________________________________
16. Gamete________________________________________________________________
17. Gene __________________________________________________________________
18. Genetic variation _________________________________________________________
______________________________________________________________________
19. Genome ________________________________________________________________
20. Genotype _______________________________________________________________
21. Haploid ________________________________________________________________
22. Heredity_______________________________________________________________
23. Heterozygous____________________________________________________________
24. Homozygous ____________________________________________________________
25. Homologous_____________________________________________________________
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26. Hybrid_________________________________________________________________
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27. Incomplete dominance_____________________________________________________
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28. Meiosis________________________________________________________________
29. Mitosis________________________________________________________________
30. Monohybrid_____________________________________________________________
31. Multicellular organism______________________________________________________
32. Non-disjunction__________________________________________________________
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33. Ovule__________________________________________________________________
34. Offspring_______________________________________________________________
35. Pedigree________________________________________________________________
36. Phenotype______________________________________________________________
37. Probability______________________________________________________________
38. Punnett Square __________________________________________________________
39. Recessive_______________________________________________________________
40. Recombinant ____________________________________________________________
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41. Replication _____________________________________________________________
42. Segregation_____________________________________________________________
43. Sex-linked______________________________________________________________
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44. Somatic cell_____________________________________________________________
45. Sperm_________________________________________________________________
46. Trait _________________________________________________________________
47. X chromosome ___________________________________________________________
48. Y chromosome ___________________________________________________________
49. Zygote ________________________________________________________________
50. Hemophilic _____________________________________________________________
51. Inheritance _____________________________________________________________
52. Mendel ________________________________________________________________
Diagram and label each stages of mitosis prior to cytokinesis
Diagram and label each stages of meiosis

Genetics Unit Study Guide – Heredity
1. One step in a single eukaryotic cell becoming two daughter cells is the process of _____________
2. The principle that describes that genes segregate without influence on each others inheritance:
3. If an organism has a gamete containing 12 chromosomes, one would expect each of its body cells to contain chromosomes.
4. Compared to the number of chromosomes contained in a body cell of a parent, how many chromosomes would normally be contained in a gamete?
5. The numbers in the figure represent the chromosome number found in each of the dog cells shown. The processes that are occurring at A and B are ______________________________.

6. Which chromosomes shown in the picture above are homologous to each other?
7. During the formation of gametes, independent assortment occurs
____________________________________________________________________________
8. Mendel’s hypothesis that two factors for each trait are segregated during the formation of gametes is explained by
9. If a corn plant has a genotype of Ttyy, what are the possible genetic combinations that could be present in a gamete (single grain of pollen) from this plant?
10. The law of independent assortment states that
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11. The law of segregation states that
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12. To describe how traits can disappear and reappear in a certain pattern from generation to generation, Mendel proposed the
13. One of the plants that the scientist is studying has an extra copy of one chromosome in all its cells. This variation most likely occurred during
14. Crossing-over most commonly results in .
BR Br bR Br
BR BBRR BBRr BbRR BbRr
Br BBRr BBrr BbRr Y
bR BbRR BbRr X
Br BbRr Bbrr
A male guinea pig with black, rough hair (BbRr) was crossed with a female guinea pig with black, rough hair (BbRr). The Punnett square contains the partial results from this mating. (B=black, b=white, R=rough, r=smooth)
15. According to the figure above, what is the genotype for X? and for Y

16. Using the diagram above, explain the pattern of inheritance for hemophilia (a blood disease) trait.
____________________________________________________________________________
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17. Above is a pedigree for the recessive trait, attached ears (aa). The dominant trait is unattached ears (A). The black circles indicate people who have the recessive trait.
Using the chart, what would be the genotype of person I,2?
Using the chart, what would be the genotype of person II,2?
XH Xh
Xh XHXh XhXh
Y XHY 4
h = hemophiliac
H = normal
18. Using the chart above, how many offspring will be hemophiliacs?
19. The phenotype of box 4 is
20. In fruit flies, the gene for red eyes (R) is dominant and the gene for sepia eyes (r) is recessive. What are the possible combinations of genes in the offspring of two red-eyed heterozygous flies (Rr)?
21. The appearance of an organism is its
22. To determine the genotype of an individual that shows the dominant phenotype, you would cross that individual with one that is
23. In a two-factor cross between an individual with the genotype RRYY and an individual with the genotype rryy, all of the offspring will have the genotype
24. A segment of DNA that controls a particular hereditary trait is called a
25. The genetic makeup of an organism is called its
26. Having two similar, dominant alleles for a trait is called
27. A cross between two plants that have pink flowers produced plants that have red, pink, or white flowers. What is the most likely explanation for these results?
28. An organism in which two alleles for a trait are different is
29. The phenotype of an organism is
30. Tallness (T) is dominant to shortness (t) in pea plants. What is the genotype of a pea plant that is heterozygous for tallness?
31. An individual heterozygous for a trait and an individual homozygous recessive for the trait are crossed and produce offspring that are of different phenotypes.
32. A scientist crossed a tall pea plant with a short pea plant. All of the four hundred offspring produced were tall pea plants. Explain these results.
33. A family has eight children. Six children have second toes that are longer than the big toe. Two children have second toes that are shorter than the big toe. What are the most likely genotypes of the parents?
34. A homozygous individual would have what possible genotype?
35. If two parents with dominant phenotypes produce an offspring with a recessive phenotype, what can you say about the parents?
36. In a monohybrid cross between two heterozygous parents, one would expect the offspring to be
37. Living things grow because
38. How are mature human sperm and eggs similar?
39. Female gametes are called
40. Each egg and sperm cell contains a haploid number of chromosomes. After fertilization, a zygote is formed have a number of chromosomes.
41. How many chromosomes are there in a human gamete?
42. A human zygote contains ________ chromosomes, fifty percent of the total coming from each parent cell.
43. Sex cells are also called
44. A fertilized egg is also called a(n)

45. Which diagram correctly illustrates the fusion of normal gametes that will most likely produce a human male?
46. A developing heart increases in size through the process of
47. A man with a certain syndrome marries a woman who is normal for that trait. They have 6 children, three girls and three boys. All four the girls have the same syndrome as the father whereas none of the boys is affected. Which type of heredity is not possible here?
48. Nondisjunction is related to a number of serious human disorders. How does nondisjunction cause these disorders?
49. What occurs during the process of meiosis in humans that can lead to a child with the condition of Down Syndrome?
50. What is the name for this process and what causes it?_____________________________________
_______________________________________________________________________________
51. A white mouse whose parents are both white produces only brown offspring when mated with a brown mouse. The white mouse is most probably ____________________________________________.
52. Given that the dominance hierarchy of rabbit fur color alleles is C>Cch>Ch, from grey to chinchilla to Himalayan, respectively what would be the percentage of Himalayan colored rabbits from parents with C Ch and Cch Ch ?
53. The diagram shows a diploid cell with two homologous pairs of chromosomes. Due to independent assortment, the possible allelic combinations that could be found in gametes produced by the meiotic division of this cell are _________________________
54. Using the figure below, which process would result in the formation of chromosome C from chromosomes A and B?
55. Suppose an animal is heterozygous AaBb, and the traits are not linked. When meiosis occurs, list out the possible combinations of gametes that can be made for these traits?
56. Suppose an animal is heterozygous AaBbCc, and the traits are not linked. When meiosis occurs, list out the total possible combinations of gametes that can be made for these traits?
57. A true-breeding tall pea plant is crossed with a true-breeding short pea plant, and all the offspring are tall. What is the most likely genotype of the offspring assuming a single-gene trait?
58. In mice, black is dominant to white color and color is determined by a single gene. Two black mice are crossed. They produce 2 black offspring and one white offspring. If the white offspring is crossed with one of its parents, what percent of the offspring are expected to be white?
59. Mendel crossed a true-breeding plant that produced green seeds with a true-breeding plant that produced yellow seeds to produce an F1 generation. The entire F1 generation produced yellow seeds. Then he crossed the F1 offspring with each other to produce the F2 generation. From the F2 generation, he counted 6022 yellow seeds. What is an estimate of the number of green seeds he collected from the F2 generation?
60. In which situation are the phenotypes of F2 offspring expected to follow the ratio of 9:3:3:1.
61. If two heterozygous individuals are crossed, what percent of their offspring are also expected to be heterozygous
62. A geneticist crossed fruit flies to determine whether two traits are linked. The geneticist crossed a fly with blistery wings and spineless bristles (bbss) with a heterozygous fly that had normal wings and normal bristles (BbSs). Which results in the next generation would suggest these traits are linked?
63. A man heterozygous for blood type A marries a woman heterozygous for blood type B. The chance that their first child will have type O blood is ____.
64. According to figure below, what is the chance that individual A will be afflicted with Huntington's?

65. Consider the cell labeled X in the figure below containing 4 chromosomes. Which of the four cells below it represents a healthy gamete that could be produced from this cell?
66. What is the best description of the events that take place during anaphase II?
67. During which phase of meiosis do homologous pairs of chromosomes line up next to one another along the equator?
68. Which stage of meiosis is responsible for the law of independent assortment?


70. What fraction of this cross will be recessive for both traits?
71. If individual III-2 marries a person with the same genotype as individual I-1, what is the chance that one of their children will be afflicted with hemophilia?
72. What type of inheritance pattern does the trait represented by the shaded symbols illustrate?
73. For the trait being followed in the pedigree, individuals II-1 and II-4 can be classified as ___________.
74. What is the relationship between individual I-1 and individual III-2?
75. The coat color in Labrador retrievers is controlled by two sets of alleles that interact epistatically. The gene E/e determines whether the fur has pigment or not and is epistatically dominant to the gene B/b, which controls the darkness of pigment when it is there. A breeder crosses a purebred black Lab, with the genotype BBEE, and a purebred yellow Lab with the genotype bbee, producing offspring that are black. A test cross is done between these offspring and an individual with the genotype bbee. What is the expected ratio of black:chocolate:yellow?
76. One step in a single eukaryotic cell becoming two daughter cells is the process of ________________.
77. How are mature human sperm and eggs similar?