Biology Chapter 11 Introduction to Genetics Mendel and

Biology Chapter 11 Introduction to Genetics: Mendel and Meiosis

IQ #1 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis? 2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo? 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Section 11 -4: Meiosis I. MEIOSIS Reduction Division A. Meiosis= process of _____________ in which the number of chromosomes per cell is cut in 1/2 and the homologous chromosomes that exist in a diploid cell are separated. (and produce haploid cells) B. Purpose= Form gametes (egg and sperm)

II. DIPLOID AND HAPLOID CHROMOSOME NUMBER fertilization A. During ________ the genetic material from one parent combines with genetic material from another Example: A fruit fly has 8 chromosomes A set of 4 came from the female fly A set of 4 came from the male fly B. The two sets of chromosomes are said to be homologous = a female chromosome has a corresponding male chromosome.

Diploid (2 n) C. =contain both sets of homologous chromosomes Haploid (n) D. = contain 1 set only Male gamete Sperm (n) = 23 chromosomes Female gamete Egg (n) = 23 chromosomes

Question: If we start with a diploid cell, how do we get an organism that produces haploid gametes? Answer: Meiosis (aka: reduction division) 1 replication; 2 divisions Example: Human what if: 46 Fruit fly 16 92 46 Duplicated 8 46 chromosomes 23 23 8 23 23 4 Duplicated chromosomes 4 4 8 4

III. PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES: MEIOSIS I & II INTERPHASE: growth, DNA synthesis, protein production, organelle production Meiosis I prophase I 1. homologous chromosomes pair up (Form tetrads) 2. nucleoli disappear 3. nucleus disappears 4. crossing-over occurs: portions of chromatids exchange genetic material 2 n (diagram 277) A.

Crossing-Over Crossing Over: exchange of genetic material between homologous chromosomes Section 11 -4 Go to Section:

Crossing-Over Section 11 -4 Go to Section: Crossing Over

metaphase I 1. homologous pairs (tetrads) line up at the equator 2. spindles attach to chromosomes independent assortment occurs anaphase I 1. spindles pull the homologous chromosomes toward opposite ends of the cell Key point: homologous pairs separate, cell now haploid

ü telophase I 1. Nuclear membranes reform 2. cell begins to separate into two new haploid cells 3. 2 haploid daughter cells n n

Figure 11 -15 Meiosis Section 11 -4 Meiosis I Interphase I Prophase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Each chromosome pairs with Spindle fibers attach to the The fibers pull the its corresponding homologous chromosomes. homologous chromosome to form a tetrad. toward the opposite ends of the cell. Go to Section: Metaphase I Anaphase I

B. Meiosis II (similar process as mitosis; no replication) Prophase II Metaphase II Anaphase II Telophase II/ Cytokinesis n n n ***RESULT: 4 haploid daughters that are genetically different!! n

Figure 11 -17 Meiosis II Section 11 -4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells.

Figure 11 -17 Meiosis II Section 11 -4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. http: //www. sumanasinc. com/webcontent/anisampl es/majorsbiology/meiosis. html

IV. GAMETE FORMATION (refer to page 278) A. Males The 4 haploid cells (gametes) = sperm 1. 2. male gametes produced by a process called _________ spermatogenesis B. Females 1. 4 haploid cells are produced but only viable egg 1 -haploid cell is a polar bodies produced by uneven cytoplasmic 3 -produce division 2. female gametes produced by a process called ________ oogenesis

(a) In the male, all four haploid products of meiosis are retained and differentiate into sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg cell and three (in some cases, only two) small cells called polar bodies that do not give rise to functional gametes. Although not indicated here, the mature egg cell has usually grown much larger than the oocyte from which it arose.

V. COMPARING MITOSIS AND MEIOSIS A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. http: //biologyinmotion. com/cell_division/ Mitosis Meiosis Number of daughter cells Type of cells produced Number of divisions Number of replications Purpose of division 2 diploid cells 4 haploid cells Body cells gametes 2 1 1 Growth, repair, asexual reproduction 1 Sexual reproduction

Section 11 -1 Standards addressed: CA 3. b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment. National 7 2. c. Students know an inherited trait can be determined by one or more genes. 7. 2. d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining phenotype while the other is recessive. B 1. 2. d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization). Key Ideas: What is the principle of dominance? What happens during segregation?

INTRODUCTION TO GENETICS I. The work of Gregor Mendel A. : the scientific study of heredity Genetics B. Heredity: Passing genes from generation to generation II. Gregor Mendel's Peas A. In the 1800's, _______________ (an Gregor Mendel Austrian Monk) conducted the first scientific study of heredity using pea plants. B. Pea plants contain both male (pollen: sperm) and female (eggs) reproductive parts.

Flowering Plant Structures: A Pea Plant C. ________ = Joining of male and female reproductive cells Fertilization

D. _________= a pea plant whose pollen Self-pollination fertilizes the egg cells in the very same flower. 1. Mendel discovered that some plants _________ for certain traits “Bred True” 2. Trait= Specific Characteristics Example: seed color, plant height 3. True breeding (aka pure)= Peas that are allowed to self-pollinate produce offspring identical to themselves Example: Short plants that self pollinate for generations always produce offspring that were pure for shortness.

Cross Pollination Self pollination

E. ________= male sex cells from one Cross-pollination flower pollinate a female sex cell on a different flower. F. Mendel manually cross pollinated pea plants, removing the male parts to ensure no selfpollination would occur. Through a series of experiments, Mendel was able to make discoveries of basic principles of heredity. 1. principle of Dominance 2. principle of Segregation 3. principle of Independent Assortment

III. Experiments Mendel performed 7 A. Mendel studied _______ different traits in pea plants each with 2 contrasting characters. (refer to page 264) B. Each trait Mendel studied was controlled by one gene. Alleles C. Different forms of a gene (trait) = Example: Gene for plant height has 2 alleles Dominant: T = tall Recessive: t = short

Figure 11 -3 Mendel’s Seven F 1 Crosses on Pea Plants Mendel’s Seven Crosses on Pea Plants Section 11 -1 Go to Section: Seed Shape Seed Color Round Yellow Seed Coat Color Gray Pod Shape Pod Color Flower Position Smooth Green Axial Tall Short Wrinkled Green White Constricted Yellow Terminal Round Yellow Gray Smooth Green Axial Plant Height Tall

Experiment #1: Parent Offspring Pure bred tall x pure bred tall TT X TT All plants are Pure bred short x pure bred short tt X tt Pure bred tall x pure bred tt short X TT All plants are TALL SHORT All plants are TALL

Conclusion: · individual factors (now known as _____) genes · the factors did not blend · ________________= some Principle of Dominance alleles are dominant (expressed trait; written as a capital letter; ex. T) some are recessive (hidden/masked trait; written as a lower case letter; ex. t) From these conclusions, Mendel wanted to continue his experiments to see what happened to the recessive trait

Principles of Dominance Section 11 -1 P Generation Tall Go to Section: Short F 1 Generation Tall F 2 Generation Tall Short

Conclusion: · ______________: The Principle of Segregation reappearance of the recessive allele indicated that at some point the allele for shortness separated from the allele for tallness. Mendel suggested that the alleles separated during the formation of the sex cells (gametes)…. During meiosis.

IV. PROBABILITY AND PUNNETT SQUARES The likelihood that a particular event A. A. Probability = will occur # of times a particular event occurs B. B. Probability= # of opportunities for the event to occur (# of trials) Example #1: If you flip a coin, what is the probability of landing on heads? 1 Probability= (side that has a head on it) ( opportunities on a coin; head or tails) 2 2 Example #2: If you flip a coin 3 times what is the probability of landing on heads? Probability= ½ x ½ = 1/8

Each flip is independent of the next. Past outcomes do not affect future ones. Similar to alleles that segregate randomly, like a coin flip larger the number of trials the closer you get B. The to the expected outcomes C. The principles of probability can be used to predict the outcomes of genetic crosses.

IV. PUNNETT SQUARES Use of Punnett squares help determine the probable outcomes of genetic crosses. · New vocabulary to help with Punnett squares Having 2 identical alleles (TT, -Homozygous = tt) -Heterozygous= Having 2 different alleles (Tt) -Genotype= Genetic makeup of an organism (TT, tt, Tt) -Phenotype= Physical appearance (tall or short) -Hybrids= The offspring resulting from a cross between parents of contrasting traits

Example of a Punnett square: Parent (P) cross homozygous tall( ) x homozygous short( ) tt TT t t · T Tt Tt Tt F 1 offspring Probability of producing homozygous tall offspring? 0/4 Probability of producing hybrid? 4/4

IV. PROBABILITY AND SEGREGATION A. For fun, lets cross F 1’s to see if Mendel’s assumption about segregation are correct: B. Tt x Tt T t T TT t Tt Tt tt If the alleles segregate during meiosis, then the probable outcomes will be: TT= 1/4 Tall= 3 Tt= 2/4 Short= 1 tt= 1/4 Ratio tall: short= 3: 1

Conclusion: Mendel was correct in his assumptions about Segregration IV. PROBABILITY AND INDEPENDENT ASSORTMENT A. Mendel wondered if one pair of alleles affected the segregation of another pair of alleles. Do round seed have to be yellow? B. The two factor cross: Mendel crossed RRYY x rryy (P)(aka: two trait cross) Hybrid (Rr. Yy) (F 1) All offspring are

A. Then he crossed the hybrids (F 1): Rr. Yy x Rr. Yy · Punnett square formatting rules for 2 trait crosses 1. Determine the possible gametes produced by the parents. 2 methods: a. F- irst two Rr. Yy O- utside two (RY) I- nside two (Ry) L- ast two (r. Y) (ry)

a. Use a punnett square. One trait on top and the other trait on the side. Parent 1: Rr. Yy Parent 2: Rr. Yy R RY r Ry R r. Y ry r Ry RY y Y y Y ry r. Y Possible gametes

2. Place one parent’s gametes at the top of a 16 Punnett square and the other parent’s gametes on the side of the 16 -Punnett square. RY Ry ry r. Y RY RRYy r. Y Rr. YY ry Rr. YY Rr. Yy Rryy rr. YY Rryy Rr. Yy Ry RRYy RRyy rr. Yy rryy

Section 11 -3 Go to Section:

9/16 Probability= RY (round and yellow)= 3/16 Ry (round and green)= 3/16 r. Y (wrinkled and yellow)= ry (wrinkled and green)= 1/16 Ratio= 9: 3: 3: 1 Alleles for seed shape independently · Conclusion= assort. Independent assortment= Genes for different traits can segregate independently during the formation of gametes ****This is true if the traits you are studying are located on different chromosomes Just by chance all 7 of Mendel’s traits were on different chromosomes.

***Summary of Mendel’s Principles*** 1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. 2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. 3. In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed. 4. The alleles for different genes usually segregate independently of one another.

Summary of Gregor Mendel’s Work Gregor Mendel experimented with Pea plants concluded that “Factors” determine traits Some alleles are dominant, and some alleles are recessive which is called the Law of Dominance Alleles are separated during gamete formation which is called the Law of Segregation

Beyond Dominant and Recessive Alleles Key idea: Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Ex. Four O’clock flowers (see figure at right) Incomplete Dominance: One allele is not completely ________ dominant over another. Therefore the phenotype in the heterozygous is somewhere _____ the two homozygous phenotypes. in between Ex. Four O’clock flowers

Incomplete Dominance in Four O’clock Flowers

equally Codominance: both alleles contribute _____ to the phenotype. Ex. Cholesterol more than two Mutliple Alleles: Genes that have _______ alleles. This does not mean an individual can have more than two alleles, but that there are more than two alleles in the ________ for a given trait. population Ex. Rabbit coat color, blood type

Multiple Alleles and Codominance 3 Alleles: i. A, i. B, I i. A and i. B are codominant i. A, i. B both dominate over i

Polygenic Inheritance: The interaction of many genes controls one trait. It is usually recognized in traits that show a __________ such as skin color, height, range of phenotypes and body weight.

Applying Mendel’s Principles. Mendel’s principles do not apply only to plants. Thomas Hunt Morgan 1. In the early ____, Morgan (a nobel prize 1900’s winning geneticist) decided to look for a model organism to advance the study of genetics. fruit fly 2. He studied the _______, Drosophila melanogaster. 3. This specimen was a good choice because: · _______ and can be kept in a small place tiny · produce ______ of offspring hundreds 4 pairs · has only _____ of chromosomes · they can produce a new ________ generation every 4 weeks

Fruit Flies (Drosophila melanogaster)

Genetics and the environment Genes alone ___________ the do not determine characteristics of an organism. The interaction between genes and the ________are necessary. environment Ex. Consider the height of a sunflower. Genes provide a plan for the development of a sunflower but the condition of the soil, climate, and water availability will also influence the height of the sunflower.

11 -5: Gene Linkage and Gene Maps Standards addressed: CA B 1 3. b students know the genetic basis for. Mendel’s laws of segregation and independent assortment. *B 1 3. d. Students know how to use data on frequency of recombination at meiosis to estimate genetic distances between loci and to interpret genetic maps of chromosomes. Key concept: What structures actually assort independently?

Actually ____________ do assort the chromosomes independently just as Mendel had suggested but the _______ on the chromosomes can be ______. linked together genes A. Linked genes 1. Genes located on the _____ same chromosome together 2. Inherited _______ 3. Do not undergo __________; independent assortment they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes. . . none were linked. )

B. Linkage group= all the genes on a _______ chromosome * If there are ___ pairs of chromosomes then there are 4 4 23 ____ linkage groups. Humans have ____ pairs of chromosomes therefore ____ linkage groups 23

III. Crossing Over A. If two genes are found on the same chromosome, does it mean that they are linked forever? NO! recombinants. Crossing over produces __________ B. Recombinants= individuals with new combinations _________ of genes

IV. Gene Mapping A. Sturtevant stated that: · crossing over occurs ________ along the randomly linkage groups. · the ________ the genes are from each further other the _______ they will cross over more likely frequency of recombination · using the ____________ (how often crossing over occurs), a gene _______ can be made map for each chromosome

B. Gene map= the _________ on a positions of genes chromosome Example: gene a and gene b cross over 20% gene a and gene c cross over 5% gene b and gene c cross over 75% chromosome: C A B

Figure 11 -19 Gene Map of the Fruit Fly Exact location on chromosomes Chromosome 2