# Introduction to Genetics: Mendel and Meiosis

## Presentation on theme: "Introduction to Genetics: Mendel and Meiosis"— Presentation transcript:

Introduction to Genetics: Mendel and Meiosis
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
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= Reduction Division Form gametes (egg and sperm)

II. DIPLOID AND HAPLOID CHROMOSOME NUMBER
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 fertilization B. The two sets of chromosomes are said to be homologous = a female chromosome has a corresponding male chromosome.

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

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

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

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

Crossing Over Go to Section:

Crossing Over Crossing-Over Go to Section:

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

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

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

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

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

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

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

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

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

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

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

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

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

Chapter 18 Sexual Reproduction, Meiosis, and Genetic Recombination Figure Gamete Formation (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. © 1999 by Addison Wesley Longman A division of Pearson Education

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. 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 1 2 1 1 Sexual reproduction Growth, replacement, repair, asexual reproduction

Key Ideas: What is the principle of dominance?
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. B1. 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 B. Heredity:  II. Gregor Mendel's Peas A. In the 1800's, _____________________________ (an 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. Genetics Passing genes from generation to generation Gregor Mendel

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

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

Cross Pollination Self pollination

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

III. Experiments Mendel performed
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. C.  Different forms of a gene (trait) = Example: Gene for plant height has 2 alleles 7 Alleles Dominant: T = tall Recessive: t = short

Mendel’s Seven Crosses on Pea Plants
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall Go to Section:

Mendel 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 short X TALL SHORT TT tt TALL

Conclusion: genes did not blend Principle of Dominance
·        individual factors (now known as _________) ·        the factors  ________________________________= some 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 did not blend Principle of Dominance

Principles of Dominance
Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

Principles of Dominance
Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

Principles of Dominance
Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short 3 tall : 1 short Go to Section:

Conclusion: ·        ___________________________: The 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. Principle of Segregation

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

C. The principles of probability can be used to
A. Each flip is   B.  The   C. The principles of probability can be used to 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 to the expected outcomes 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  -Homozygous =  -Heterozygous= -Genotype= -Phenotype= -Hybrids= Having 2 identical alleles (TT, tt) Having 2 different alleles (Tt) Genetic makeup of an organism (TT, tt, Tt) Physical appearance (tall or short) The offspring resulting from a cross between parents of contrasting traits

homozygous tall( ) x homozygous short( ) TT tt
·        Example of a Punnett square: Parent (P) cross homozygous tall( ) x homozygous short( ) TT tt t t T Tt Tt T Tt Tt F1 offspring Probability of producing homozygous tall offspring? Probability of producing hybrid? 0/4 4/4

IV. PROBABILITY AND SEGREGATION
For fun, lets cross F1’s to see if Mendel’s assumptions about segregation are correct: Tt x Tt T t T TT Tt t Tt tt If the alleles segregate during meiosis, then the probable outcomes will be: TT= Tall= Tt= Short= tt= Ratio tall:short= 1/4 3 2/4 1 3:1 1/4

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.  B.The two factor cross: Mendel crossed RRYY x rryy (P)(aka:two trait cross) All offspring are Do round seeds have to be yellow? Hybrid (RrYy) (F1)

A.   Then he crossed the hybrids (F1):
RrYy x RrYy ·  Punnett square formatting rules for 2 trait crosses 1. Determine the possible gametes produced by the parents. 2 methods: a.    F- RrYy O- I- L- irst two (RY) utside two (Ry) (rY) nside two (ry) ast two

a. Use a punnett square. One trait on top and the
a.  Use a punnett square. One trait on top and the other trait on the side. Parent 1: RrYy Parent 2: RrYy Y y Y y R RY Ry Ry R RY r r rY ry rY ry Possible gametes 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 ry RRYY RRYy RrYY RrYy RY RRYy RRyy RrYy Rryy Ry rY RrYY RrYy rrYY rrYy rryy Rryy rrYy ry RrYy

Alleles for seed shape independently assort.
Section 11-3 Probability: RY (round and yellow)= Ry (round and green = rY (wrinkled and yellow)= ry (wrinkled and green)= Phenotype Ratio=   Conclusion= 9/16 3/16 3/16 1/16 9:3:3:1 Alleles for seed shape independently assort. Go to Section:

Independent assortment
Genes for different traits can segregate independently during the formation of gametes ****This is true if the traits you are studying Just by chance all 7 of Mendel’s traits were on different chromosomes. are located 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
experimented with concluded that “Factors” determine traits Alleles are separated during gamete formation Pea plants Some alleles are dominant, and some alleles are recessive which is called the which is called the Law of Dominance 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 next slide)

Incomplete Dominance in Four O’clock Flowers
Incomplete Dominance: One allele is _______________ dominant over another. Therefore the phenotype in the heterozygous is somewhere __________ the two homozygous phenotypes. not completely in between

Incomplete Dominance in Four O’clock Flowers

Codominance: both alleles contribute _________ to the phenotype.
Ex. Cholesterol   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. Ex. Rabbit coat color, blood type equally more than two population

Multiple Alleles and Codominance
iA, iB, I iA and iB are codominant iA, iB both dominate over i Blood Type/Phenotype BO BB

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

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

Fruit Flies (Drosophila melanogaster)

Genetics and the environment
Genes alone ______________________ the characteristics of an organism. The interaction between genes and the ________________are necessary. 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. do not determine environment

11-5: Gene Linkage and Gene Maps
Standards addressed: CA B1 3.b students know the genetic basis forMendel’s laws of segregation and independent assortment. *B1 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 independently just as Mendel had suggested but the _______ on the chromosomes can be ____________. A. Linked genes 1. Genes located on the _________ chromosome 2. Inherited _____________ 3. Do not undergo ___________________; they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes...none were linked.) the chromosomes genes linked together same together independent assortment

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

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

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

B. Gene map= the __________________ on a 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% positions of genes C A B chromosome:

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