Biology of the Human Body NSCI352 Dr. Ekaterina (Kate) Vorotnikova E-mail: evorotnikova@hesser.edu Lecture 11. Cell Reproduction Chapter 18 (Page 354-360; 362-369) Introduction to Genetics Chapter 19 (Page 374-378)

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

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.

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

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

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

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

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

Animation: Chromosome structural organization

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

The Usual Chromosome Number for Humans Cells Is Forty-Six

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!

Mitosis Maintains Diploid Chromosome Number from One Generation to Next

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

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

Animation: Duplicating chromosome

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

Animation: The cell cycle

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

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. 18-7 (a-d), p. 358

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. 18-7 (e-h), p. 359

Animation: Mitosis step-by-step

Animation: Mitosis

Animation: Cytoplasmic division

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

Animation: Sperm formation

Oogenesis Is the Process That Forms Eggs

Animation: Egg formation

Animation: Meiosis I and II

A Visual Tour of the Stages of Meiosis

Animation: Meiosis step-by-step

Animation: Meiosis

Animation: Crossing over

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).

Animation: Random alignment

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

Mitosis Maintains the Chromosome Number of the Parent Cell

Meiosis Reduces the Chromosome Number by Half

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. 18-17, p. 371

Introduction to Genetics Chapter 19 (page 374-378)

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.

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

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

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

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.

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

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.

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.

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)

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.)

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

F1 generation: all plants with purple flowers

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

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

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.

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.

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

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

Animation: Chromosome segregation

Animation: Monohybrid cross

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.

Many Genetic Traits Have Dominant and Recessive Forms

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

Animation: Genetic terms

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

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

Different Genetic Results Possible in Second Generation after Monohybrid Mating

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

Animation: Testcross

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

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

Independent Assortment: Chromosomes Moved at Random into Forming Gametes

Animation: Independent assortment

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

Animation: Sickle-cell anemia

Animation: Symptoms of sickle-cell anemia

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

Animation: Codominance: ABO blood types

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

Homework (from Student Interactive Workbook) Write the answers in your Student Interactive Workbook: Page 283-286; 289-291; 297-298 Page 302-305; !!!Write on a piece of paper answers to the following questions: page 300-301 - 2, 5, 6, 10, 19; page 311- 1, 4, 6, 10, 11. Give to the instructor before the class!!!!