1. Biology of the Human Body NSCI352
Dr. Ekaterina (Kate) Vorotnikova
Lecture 11.
Cell Reproduction
Chapter 18
(Page ; )
Introduction to Genetics
Chapter 19
(Page )

2. Cell Reproduction Chapter 18 (page 354-360; 362-369)

3. Objectives
Be able to describe a chromosome and tell the numbers found in sex and non-sex cells.
Understand the cell cycle and be able to visualize where mitosis fits into the cell cycle.
Be able to describe each phase of mitosis.
Understand the effect that meiosis has on chromosome number.
Describe the events that occur in each meiotic phase.
Compare mitosis and meiosis; cite similarities and differences.

4. Reproduction Produces a new generation of cells
Produces a new individual
Part of the life cycle; series of recurring events in which individuals:
Grow
Develop
Maintain themselves
Reproduce

5. Mitosis Meiosis Division of somatic cells Purpose
Growth
Replace worn out or dead cells
Repair tissue
Meiosis
Division of germ cells
First stage in sexual reproduction

7. Chromosome
Very long DNA molecule in association with protein
Gene
Segment of DNA in a chromosome
Chromatin
DNA and protein combined

8. Eukaryotic chromosomes are composed of chromatin
Chromatin = DNA + proteins
To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope
Early in the division process, chromosomes duplicate
Each chromosome appears as two sister chromatids, containing identical DNA molecules
Sister chromatids are joined at the centromere, a narrow region

9. The large, complex chromosomes of eukaryotes duplicate with each cell division

10. Animation: Chromosome structural organization

11. Having Two Sets of Chromosomes Makes a Cell Diploid
Chromosome number
Sum of chromosomes in a given type of cell
Humans have 46; 23 from each parent
Diploid (2n): two sets of chromosomes
Autosomes: pairs 1–22
Sex chromosomes
XX in females
XY in males
Homologous chromosomes
Paired corresponding chromosomes

12. The Usual Chromosome Number for Humans Cells Is Forty-Six

13. The human sex chromosomes X and Y differ in size and genetic composition
Applying Your Knowledge
Humans have 46 chromosomes; how many homologous pairs does that represent? 23
If there is one pair of sex chromosomes, how many pairs of autosomes are found in humans? 22
Student Misconceptions and Concerns
1. Some students might conclude that sex chromosomes function only in determining the sex of the individual. As the authors note, sex chromosomes contain genes not involved in sex determination.
Teaching Tips
1. Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait discussed in Module 8.12.
2. Consider helping students through mitosis and meiosis by developing an analogy to pairs of shoes. In this case, any given species has a certain number of pairs of shoes, or homologous chromosomes.
3. In the shoe analogy, females have 23 pairs of matching shoes, while males have 22 matching pairs and 1 odd pair Maybe a sandal and a sneaker!

14. Mitosis Maintains Diploid Chromosome Number from One Generation to Next

15. Having Only One Set of Chromosomes Makes a Cell Haploid
Meiosis
Reductional division
Reduces the number of chromosomes to a haploid number (n)
Occurs in spermatogonia or oogonia

16. Duplicated chromosomes
Attach to the spindle
Two sets of microtubules extending from the centrioles
Overlap in the “equator” region
Sister chromatids moved via the spindle apparatus

17. Animation: Duplicating chromosome

18. The Cell Cycle
Every time a new cell comes into being, a multistep cell cycle begins anew
Cell cycle
“Lifetime” of a somatic cell
Varies depending on cell type
Interphase
G1: cell growth
S: DNA copied and its chromosomes are duplicated
G2: Preparation for mitosis
Mitosis: chromosomes sorted into two sets and the cytoplasm divides; four phases

19. Animation: The cell cycle

20. The Four Stages of Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
After Mitosis, Daughter Cells Have Same Chromosome Number as Parent Cell

21. Figure 18.7: Animated! Mitosis ensures that daughter cells will have the same chromosome number as the parent cell.
For clarity, the diagram shows only two pairs of chromosomes from a diploid (2n) animal cell.
Fig (a-d), p. 358

22. Figure 18.7: Animated! Mitosis ensures that daughter cells will have the same chromosome number as the parent cell.
For clarity, the diagram shows only two pairs of chromosomes from a diploid (2n) animal cell.
Fig (e-h), p. 359

23. Animation: Mitosis step-by-step

24. Animation: Mitosis

25. Animation: Cytoplasmic division

26. Meiosis: The Beginnings of Eggs and Sperm
Meiosis divides the nuclei of germ cells in a way that halves the number of chromosomes in daughter cells
Spermatogenesis
Diploid germ cell increases in size
This primary spermatocyte → four haploid spermatids → change in form to become sperm

27. Animation: Sperm formation

28. Oogenesis Is the Process That Forms Eggs

29. Animation: Egg formation

30. Animation: Meiosis I and II

31. A Visual Tour of the Stages of Meiosis

32. Animation: Meiosis step-by-step

33. Animation: Meiosis

34. Animation: Crossing over

35. Three sources of genetic variability in sexually reproducing organisms:
1) independent orientation of chromosomes at metaphase I (random alignment) (223 = 8 million)
2) random fertilization (64 trillion possibilities)
3) crossing over during prophase I of meiosis (1 to 3 crossover events occur per chromosome pair).

36. Animation: Random alignment

37. Animation: Comparing mitosis and meiosis (Mitosis occurs in somatic cells, while meiosis takes place in germ cells)

38. Mitosis Maintains the Chromosome Number of the Parent Cell

39. Meiosis Reduces the Chromosome Number by Half

40. each chromosome duplicated during interphase
germ cell
germ cell
each chromosome duplicated during interphase n
MEIOSIS I
separation of homologues
MEIOSIS II separation of sister chromatids
Figure 18.17: Meiosis reduces the chromosome number by half.
gametes
gametes 2n
diploid number restored at fertilization
zygote
Fig , p. 371

41. Introduction to Genetics Chapter 19 (page 374-378)

42. Objectives Be able to distinguish between “genes” and “alleles.”
Know Mendel’s principles of dominance and segregation.
Understand how to solve genetics problems that involve monohybrid and dihybrid crosses.
Understand the variations that can occur in observable patterns of inheritance.
Explain how a given pair of genes on homologous chromosomes can separate during meiosis.

43. Video: ABC News: All in the family: Mixed race twins

44. Basic Concepts of Heredity
Genes provide the instructions for all human traits, including physical features and how body parts function
Each person inherits a particular mix of maternal and paternal genes
Genes
Humans have ~21,500
Chemical instructions for building proteins
Locus: specific location on a chromosome
Diploid cells contain two copies of each gene on pairs of homologous chromosomes
Allele: each version of a gene

45. MENDEL’S LAWS
Gregor Mendel, Brunn, Austria ( now Brno, Czech Republic)

46. Experimental genetics began in an abbey garden
Gregor Mendel discovered principles of genetics in experiments with the garden pea
Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes)
Advantages of using pea plants
Controlled matings
Self-fertilization or cross-fertilization
Observable characteristics with two distinct forms
True-breeding strains
Student Misconceptions and Concerns
1. The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet, Mendel’s selection of pea plant traits typically showed complete dominance, rather than the possibility for such gradual inheritance.
Teaching Tips
1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

47. Petal
Figure 9.2B Anatomy of a garden pea flower (with one petal removed to improve visibility).
Pollen is usually transferred from the stamens to the egg-bearing carpel of the same flower, since these structures are surrounded by the petals.
Stamen
Carpel

48. pollen from stamens of white flower to carpel of purple flower Parents
White 1
Removed
stamens from
purple flower
Stamens
Carpel 2
Transferred
pollen from stamens of white
flower to carpel of purple flower
Parents
(P)
Purple
Figure 9.2C Mendel’s technique for cross-fertilization of pea plants.
This slide demonstrates how Mendel could control matings between pea plants. He removed the pollen-bearing structures from one parental plant and transferred pollen from another parental plant. The true-breeding parental plants are called the P generation, their offspring are the F1 generation, and offspring of an F1  F1 cross are the F2 generation.

49. pollen from stamens of white flower to carpel of purple flower Parents
White 1
Removed
stamens from
purple flower
Stamens
Carpel 2
Transferred
pollen from stamens of white
flower to carpel of purple flower
Parents
(P)
Purple 3
Pollinated carpel
matured into pod
Figure 9.2C Mendel’s technique for cross-fertilization of pea plants.
This slide demonstrates how Mendel could control matings between pea plants. He removed the pollen-bearing structures from one parental plant and transferred pollen from another parental plant. The true-breeding parental plants are called the P generation, their offspring are the F1 generation, and offspring of an F1  F1 cross are the F2 generation.

50. Parents (P) Offspring (F1)
White 1
Removed
stamens from
purple flower
Stamens
Carpel 2
Transferred
pollen from stamens of white
flower to carpel of purple flower
Parents
(P)
Purple 3
Pollinated carpel
matured into pod 4
Planted seeds
from pod
Figure 9.2C Mendel’s technique for cross-fertilization of pea plants.
This slide demonstrates how Mendel could control matings between pea plants. He removed the pollen-bearing structures from one parental plant and transferred pollen from another parental plant. The true-breeding parental plants are called the P generation, their offspring are the F1 generation, and offspring of an F1  F1 cross are the F2 generation.
Offspring
(F1)

51. Trait –each variant of a character (purple or white flowers, axial or terminal flower position, yellow or green seeds, round or wrinkled seeds, etc.)
Character – a heritable feature that varies among individuals (flower color, flower position, seed color, seed shape, etc.)

52. Mendel’s law of segregation describes the inheritance of a single character
Example of a monohybrid cross Parental generation: purple flowers  white flowers
Monohybrid cross – when the parents differ in only one character

53. F1 generation:
all plants with purple flowers

54. F2 generation:
3/4 of plants with purple flowers;
¼ of plants with white flowers

55. Mendel needed to explain
Why one trait seemed to disappear in the F1 generation
Why that trait reappeared in one quarter of the F2 offspring

56. A homozygous genotype has identical alleles
Four Hypotheses
Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene
For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different
A homozygous genotype has identical alleles
A heterozygous genotype has two different alleles
There is an allele for purple flower color and a different allele for white flower color.
Student Misconceptions and Concerns
1. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.
Teaching Tips
1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.
2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.
3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).
4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).
5. Figure 9.4 can be of great benefit when introducing genetic terminology of genes. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture.

57. The phenotype is the appearance or expression of a trait
Four Hypotheses
3. If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect
The phenotype is the appearance or expression of a trait
The same phenotype may be determined by more than one genotype
4. Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene
In reference to hypothesis 3, in the F1 generation, plants received a purple allele from one parent and a white allele from the other. The purple allele is dominant since all the F1 plants have purple petals.
In reference to hypothesis 4, in general, a dominant allele provides instructions for producing a functional protein. A recessive allele may lead to a nonfunctional protein or the complete absence of the protein.
Mendel needed to explain:
Why one trait seemed to disappear in the F1 generation—This is explained by dominance of the purple allele over the white allele.
Why that trait reappeared in one fourth of the F2 offspring—This is explained by the segregation of alleles, the generation of all possible combinations of gametes, and the dominance of the purple allele.
Student Misconceptions and Concerns
1. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.
Teaching Tips
1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.
2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.
3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).
4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).
5. Figure 9.4 can be of great benefit when introducing genetic terminology of genes. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture.

58. Each Pair of Gene Alleles Is Separated and Two Alleles End Up in Different Gametes

59. Genotype – genetic makeup
Genetic makeup (alleles)
P plants
Genotype – genetic makeup PP pp
Gametes
All P
All p
F1 plants
(hybrids)
All Pp
Phenotype –
expression, or physical appearance of traits
Gametes 1 – 2 P 1 – 2 p
Sperm
Figure 9.3B Explanation of the crosses in Figure 9.3A.
A Punnett square is used to show all possible fertilization events for parental gametes. In three quarters of the F2 genotypes, there will be at least one dominant allele. P p
F2 plants
Phenotypic ratio
3 purple : 1 white P PP Pp
Punnettsquare
Eggs
Genotypic ratio
1 PP : 2 Pp : 1 pp p Pp pp

60. Animation: Chromosome segregation

61. Animation: Monohybrid cross

62. Homologous chromosomes bear the alleles for each character
For a pair of homologous chromosomes, alleles of a gene reside at the same locus
Homozygous individuals have the same allele on both homologues
Heterozygous individuals have a different allele on each homologue
Student Misconceptions and Concerns
1. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.
Teaching Tips
1. Figure 9.4 can be of great benefit when introducing genetic terminology of genes. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture.
Copyright © 2009 Pearson Education, Inc.

63. Many Genetic Traits Have Dominant and Recessive Forms

64. Allele: each version of a gene
Homozygous condition: identical alleles
Heterozygous condition: different alleles
Dominant allele
Effect masks recessive allele paired with it
Genetic representations
Homozygous dominant (PP)
Homozygous recessive (pp)
Heterozygous (Pp)
Genotype
Inherited alleles
Phenotype
Observable functional or physical traits

65. Animation: Genetic terms

66. Genetic Tools: Testcrosses and Probability
When potential parents are concerned about passing a harmful trait to a child, genetic counselors must try to predict the likely outcome of the mating
PROBABILITY
Measure of the chance that some particular outcome will occur
Factor in the inheritance of single-gene traits
Cross CC x cc
All of the offspring will be heterozygous, Cc
Cross Cc x Cc
¼ CC, ½ Cc, and ¼ cc

67. A Punnett Square Can Be Used to Predict the Result of a Genetic Cross
Grid used to determine possible outcomes of genetic crosses
Rules of probability apply because fertilization is a chance event
Possibility can be expressed mathematically, e.g., between 0% and 100%
Most probable outcome does not have to occur
In a given situation, probability does not change

68. Different Genetic Results Possible in Second Generation after Monohybrid Mating

70. A Testcross Also Can Reveal Genotypes
Learn the genotype of a (nonhuman) organism
Cross organism with homozygous recessive organism (aa)
If all offspring are Aa, parent was probably AA
If some of the offspring have the dominant trait and some have the recessive trait, parent was Aa

71. Animation: Testcross

72. How Genes for Different Traits Are Sorted into Gametes
When we consider more than one trait, we see that the gene for each trait is inherited independently of the gene of other traits

73. How Genes for Different Traits Are Sorted into Gametes
Independent assortment
Occurs during meiosis
A given chromosome and its genes move randomly into gametes
Metaphase I
Metaphase II
Crosses between individuals heterozygous for two traits yields sixteen different gamete unions
Probability displayed using a Punnett square

74. Independent Assortment: Chromosomes Moved at Random into Forming Gametes

75. Animation: Independent assortment

76. Single Genes, Varying Effects
Some traits have clearly dominant and recessive forms
For most traits, however, the story is not so simple

77. Animation: Sickle-cell anemia

78. Animation: Symptoms of sickle-cell anemia

79. In Codominance, More Than One Allele of a Gene Is Expressed
Heterozygous for a trait, but both alleles are expressed
Example: alleles for blood type determine presence or absence of polysaccharides on surface of red blood cells
IA and IB; codominant when paired with each other
Multiple allele system
A gene that has three or more alleles

80. Animation: Codominance: ABO blood types

81. Conclusion Cell division. Mitosis. Meiosis.
Basic concepts of heredity: genes, alleles.
Monohybrid crosses.
Pleiotropy and codominance.

82. Homework (from Student Interactive Workbook)
Write the answers in your Student Interactive Workbook:
Page ; ;
Page ;
!!!Write on a piece of paper answers to the following questions:
page , 5, 6, 10, 19; page , 4, 6, 10, 11.
Give to the instructor before the class!!!!