is the scientific study of. Gregor Mendel was an Austrian monk. He is considered the of genetics. Mendel carried out his work with ordinary garden.

Transcription

1 11-1 The 11-1 Work of Gregor Mendel The Work of Gregor Mendel is the scientific study of. Gregor Mendel was an Austrian monk. He is considered the of genetics. Mendel carried out his work with ordinary garden.

2 Mendel's Peas Mendel studied seven pea plant (genes), each with two contrasting (alleles). A trait is a specific that from one individual to another. Mendel crossed (mated) plants with each of the seven contrasting traits and studied their.

3 Genes and Dominance Mendel s on Pea Plants 1 Crosses Mendel s F1 Crosses onfpea Plants Mendel obtained the same results for all seven characters!

4 Gregor Mendel s Peas Mendel knew that......the male part of each flower (stamens) produce pollen (containing ), and the female part of the flower (pistil) produces cells.

5 During sexual reproduction, sperm and egg cells join in a process called. Fertilization produces a new cell, the. Pea flowers are self-. Sperm cells in pollen fertilize the egg cells in the flower. The seeds and plants that are produced by self-pollination all of their characteristics from the single plant that bore them. Gregor Mendel s Peas

6 Gregor Mendel s Peas Mendel started with (pure) pea plants, but did not want them to -pollinate. Mendel wanted to - two different plants, so he cut away the pollen-bearing parts and dusted the plant s flower with pollen from another plant.

7 Genes and Dominance Each original pair of plants is the P ( ) generation. The offspring are called the F1, or first, generation. The offspring of crosses between parents with different traits are called. The F1 hybrid plants all had the trait of only one of the parents.

8 Mendel's first conclusion was that biological inheritance is determined by passed from one generation to the next. Today, scientists call the factors that determine traits. Each of the characters Mendel studied was controlled by one gene that occurred in two contrasting forms ( ) that produced different traits for each character. Mendel s second conclusion is called the principle of. Genes and Dominance

9 Genes and Dominance The principle of dominance states that some alleles are dominant and others are. An organism with a dominant allele for a trait will always that form of the trait. An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is.

10 Segregation Mendel the F1 generation to produce the (second filial) generation. The traits controlled by recessive alleles in of the F2 plants.

11 Segregation Mendel inferred that a dominant allele had the corresponding recessive allele in the generation.

12 Segregation The controlled by the recessive allele showed up in some of the F2 plants. The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or, from the allele for tallness.

13 Mendel suggested that the alleles for tallness and shortness in the F1 plants from each other during the formation of the sex cells, or. Segregation When each F1 plant produces gametes, the two alleles segregate from each other so that each carries only a copy of each gene. Therefore, each F1 plant produces types of gametes those with the for tallness, and those with the for shortness.

14 Mendel needed to check his work, so he -pollinated each plant to produce the generation. This supported his hypothesis about the alleles each F2 offspring received. When he self-pollinated the short plants, all the offspring were. When he self-pollinated of the tall plants, all of the offspring were. When he self-pollinated of the tall plants, the offspring showed the same ratio as the F2 generation.

15 Punnett Squares The likelihood that a particular event will occur is called. The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a. Punnett squares can be used to and compare the genetic that will result from a cross. F1 F2 A capital letter represents the dominant allele (T = ). A lowercase letter represents the recessive allele (t = ). produced by each F1 parent are shown along the top and left side. Possible combinations for the F 2 offspring appear in the four boxes.

16 Punnett Squares All of the tall plants have the same, or physical characteristics (tall). But they do not have the same, or genetic makeup. One third of the tall plants are TT. Organisms that have two identical alleles for a particular character are said to be or true-breeding. Two thirds of the tall plants are Tt. Organisms that have two different alleles for the same character are or hybrid. TT Homozygous Tt Heterozygous

17 11-2 Probability & Punnett Squares One fourth (1/4) of the F2 plants have two alleles for tallness (TT, homozygous, homozygous tall). Probability & Segregation F1 Two fourths (1/2) have one allele for tall and one for short (Tt, ). One fourth (1/4) of the F2 have two alleles for short (tt, homozygous, homozygous short). F2 Because the allele for tallness (T) is dominant over the allele for shortness (t), of the F2 plants should be tall. The ratio of tall plants (TT or Tt) to short (tt) plants is. The predicted ratio showed up in Mendel s experiments indicating that did occur.

18 Probabilities Predict Averages Probabilities predict the outcome of a large number of events. Probability cannot predict the outcome of an individual event. In genetics, the the number of offspring, the the resulting numbers will get to values. Tt Segregation of alleles into eggs Tt Segregation of alleles into sperm Sperm 1 T T T T 1 2 T 1 2 t T t 1 4 r Eggs t t t 1 4

19 Punnett Square Practice In pea plants, round seeds are dominant over wrinkled. Find the genotypic and phenotypic ratios of a cross between one homozygous round plant and one homozygous wrinkled plant.

20 Punnett Square Practice In pea plants, round seeds are dominant over wrinkled. Find the genotypic and phenotypic ratios of a cross between two heterozygous plants.

21 Punnett Square Practice In pea plants, yellow peas are dominant over green. You are conducting genetic experiments with this character and you need to find out the genotype of a plant with yellow pods. Draw punnett squares to show the two possible outcomes of a test-cross for this trait.

22 11-3 Exploring Mendelian Genetics Independent Assortment To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a twofactor cross (AKA Cross). The Dihybrid Cross: F1 Mendel crossed plants that produced round yellow peas (genotype ) with true-breeding plants that produced wrinkled green peas (genotype ). All of the F1 offspring produced round yellow peas (genotype ). He then crossed the F1 offspring.

23 The Dihybrid Cross F2: R r Mendel crossed the heterozygous plants with each other to determine if the alleles would segregate from each other in the generation. Independent Assortment Y y R r Y y The Punnett square predicts a ratio in the F2 generation. Mendel's experimental results were very to this. He had discovered the principle of independent assortment.

24 Punnett Square Practice In pea plants, round seeds are dominant over wrinkled and yellow peas are dominant over green. Find the phenotypic ratio of a cross between two plants heterozygous for both characters (dihybrids).

25 Independent Assortment The principle of independent assortment states that genes for different traits can independently during the formation of. Independent assortment helps account for the many genetic observed between individual organisms of the same species. (You don't look like your parents.)

26 A Summary of Mendel's Principles 1) Hypothesis: Genes are passed from parents to their offspring as discrete particles. (vs. the hypothesis.) 2) Principle of : Some forms of the gene may be dominant and others may be recessive. 3) Principle of : In most sexually reproducing organisms, each adult has two copies of each gene which are segregated from each other when gametes are formed. 4) Principle of Assortment: The alleles for different genes usually segregate independently of one another.

27 Beyond Dominant and Recessive Alleles RR When one allele is not completely dominant over another it is called dominance. In incomplete dominance, the heterozygous phenotype is the two homozygous phenotypes and the genotypic and phenotypic ratios are the. A cross between red (RR) and white (WW) four o clock plants produces -colored flowers ( ). WW

28 In, both alleles contribute to the phenotype. In certain varieties Beyond Dominant and Recessive Alleles of chickens, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens are speckled with both black and white feathers. Genes that are controlled by more than two alleles are said to have alleles. An individual can t have more than alleles. However, more than two possible alleles can exist in a. The inheritance of A, B, O blood groups is an example of codominance between the A & B alleles and multiple alleles, since there are three (IA, IB & io).

29 Beyond Dominant and Recessive Alleles Multiple Alleles: Different combinations of four alleles result in the rabbit coat colors shown here. KEY C= full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch Albino: cc ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles

30 Beyond Dominant and Recessive Alleles Traits controlled by two or more genes are said to be traits. Polygenic traits exhibit an or quantitative effect producing a of variation in a population. AaBbCc aabbcc Aabbcc 20 Fraction of progeny color in humans is a polygenic trait controlled by more than different genes AaBbcc AaBbCc AABbCc AaBbCc AABBCC AABBCc

31 Applying Mendel's Principles Thomas Hunt used fruit flies to advance the study of genetics. Morgan and others tested Mendel s principles and learned that they applied to organisms. Morgan also was the first to demonstrate experimentally that are on.

32 Applying Mendel's Principles Mendel s principles can be used to study inheritance of traits and to calculate the of certain traits appearing in the next generation.

33 Genetics and the Environment Nature vs. Nurture Characteristics of any organism are determined by the interaction between genes and the. These Hydrangea can be blue, violet or pink depending on the soil ph.

34 11-4 Meiosis 11-4 Meiosis During reproduction, each organism must inherit a copy of every gene from each of its parents. Gametes are formed by a process that the two sets of genes so that each gamete ends up with just set. Meiosis

35 All organisms have different of chromosomes. A body cell ( ) in an adult fruit fly has chromosomes: from its mother, and from its father. These two sets of chromosomes are. Each of the four chromosomes that came from the male parent has a corresponding chromosome from the female parent. Chromosome Number A cell that contains both sets of homologous chromosomes is said to be (2N). For Drosophila, the diploid number is. The gametes of sexually reproducing organisms contain only a set of chromosomes, and therefore only a single set of. These cells are (N). For Drosophila, the haploid number is.

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37 Phases of Meiosis Meiosis I Interphase I Meiosis I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Meiosis is a process of division in which the number of chromosomes per cell is cut in through the separation of chromosomes in a diploid cell. Meiosis involves divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid parent cell that entered meiosis has become haploid cells.

38 Phases of Meiosis Interphase I Cells undergo a round of DNA, forming chromosomes. AS MITOSIS! Prophase I occurs, each chromosome pairs with its corresponding chromosome to form a (4 chromatids). THAN MITOSIS!

39 Phases of Meiosis When homologous chromosomes form tetrads in meiosis, they portions of their in a process called. Crossing-over produces new combinations of alleles, increasing. THAN MITOSIS!

40 Phases of Meiosis Metaphase I fibers attach to the and they line up in pairs along the of the cell. THAN MITOSIS! Anaphase I The spindle fibers pull the homologous, chromosomes toward opposite ends of the cell. THAN MITOSIS!

41 Phases of Meiosis Nuclear form. Division of the and plasma membrane occurs. The two cells produced by meiosis I are and have chromosomes and that are different from each other and from the diploid cell. Telophase I & Cytokinesis THAN MITOSIS Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through DNA, yet each of the cell s chromosomes still have 2.

42 Phases of Meiosis Meiosis II (Mitosis- ) Telophase and Cytokinesis II II II II and Cytokinesis II

43 Prophase II Meiosis I results in two (N) daughter cells, each with the number of chromosomes as the original cell. Phases of Meiosis Metaphase II The chromosomes line up in the of the cell.

44 Phases of Meiosis Anaphase II The sister separate and move toward opposite of the cell. Telophase II & Cytokinesis Meiosis II results in haploid (N) daughter cells.

45 Spermatogenesis Gamete Formation In organisms, meiosis results in equal-sized called sperm through the process of.

46 Oogenesis Gamete Formation In many female organisms, only egg results from meiosis during the process of. The other three cells, called bodies, are usually not involved in reproduction.

47 Comparing Mitosis and Meiosis s/majorsbiology/meiosis.html Mitosis Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during before begins Number of divisions One, including prophase, metaphase, anaphase, and telophase, each including prophase, metaphase, anaphase, and telophase Synapsis of homologous choromosomes forming tetrads Number of daughter cells and genetic composition Does not occur Occurs during, forming ( groups of four chromatids); is associated with between -sister chromatids Two, each diploid(2n) and genetically identical to the parent cell, each (n), containing half as many chromosomes as the parent cell; genetically from the parent cell and from. Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth and tissue repair Produces ; reduces number of chromosomes by and introduces genetic among the gametes

48 11-5 Linkage & Gene Maps All the genes found on one chromosome are said to be. In Drosophilla, the gene for eye color is on the chromosome. This is known as a sex- character or trait. Linkage

49 Gene Mapping Crossover can be used to map on. The greater the crossover frequency between two genes, the they are on the chromosome and the more the gene appears to assort. This is why Mendel's results followed the laws of for all 7 of the characters he studied. He was!