Chapter 11: Genetics

11.1 The Work of Gregor Mendel Genetics: study of Heredity, or the passing of characteristics from parents to offspring. Traits: Inherited characteristics. Examples: eye color, red hair, height …. http://www.writing.ucsb.edu/faculty/samuels/dna.jpg

Gametes: The sex cells found in an individual- egg or sperm. Fertilization: The uniting of male and female gametes.

Mendel’s Peas Gregor Mendel (1822-1884): An Austrian monk. He wanted to know how traits were passed from parent to child. Studied pea plants.

He mated short plants with tall plants. All the offspring were tall!! Mendel started out with plants that he knew would only produce tall and pea plants that only produces short offspring. He mated short plants with tall plants. All the offspring were tall!! http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ge/m2/s2/assets/images/gem2s2_1.jpg

Tall Short Tall Tall Tall Tall Tall Short

The parental generation: P1 generation The first generation of offspring: F1 generation The second generation of offspring: F2 generation http://www.fastplants.org/graphics/genetics/parent_F2.jpg

The resulting plants were tall ¾ of the time, and short ¼ of the time! Mendel had the new tall offspring (F1 plants) self-pollinate and observed the second generation (F2 Plants). The resulting plants were tall ¾ of the time, and short ¼ of the time! http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/graphics/02Q.gif

What did Mendel concluded about trait inheritance? factors are passed from generation to generation. Genes: Factors that determine traits. Ex. Hair and eye color, height

There are two alleles that determine trait inheritance. Alleles: A particular form of a gene, one comes from the mother, one from the father. Ex. Gene = height, the allele could be tall or short. Gene = eye color, the allele could be light or dark. http://ghs.gresham.k12.or.us/science/ps/sci/soph/genetics/alleles.gif

The Role of Dominance If there are two alleles, and only one observed trait, which allele is dominant? A dominant allele is always expressed. A recessive allele not expressed when in the presence of a dominant allele. is expressed when paired with another recessive allele. http://wellspring.isinj.com/bio/principlesI/Images/segregation.jpg

Tt Male T T Female t t Punnett square:

Phenotype is the physical appearance. T is dominant to t which is recessive. Genotype is the genes. Phenotype is the physical appearance.

T is dominant to t which is recessive. TT = homozygous dominant Tt = heterozygous tt = homozygous recessive

Law of SEGREGATION Mendel’s first law. Segregation= separation of two alleles during gamete formation each gamete receives one of the two alleles.

Law of Independent Assortment Segregation + Independent assortment = four possible combinations of alleles. Law of Independent Assortment states traits like shape and seed color are inherited independently of each other.

Each F1 has a tall and short allele (for the gene for height) that it can pass on to its offspring (F2)

11.2 Punnett Squares - A diagram used to show what might result from a genetic cross. - Used to predict variations

11.3 Mendelian Genetics Monohybrid cross: one gene. Each parent donates one allele to the offspring

Homozygous: Two of the same allele for a trait. Ex. TT or tt. Purebreds Heterozygous: Two different alleles for one trait. Ex. Tt. TT is homozygous dominant. tt is homozygous recessive. Tt is heterozygous.

Dihybrid Cross (Two factor cross) Ex. Wrinkled and yellow peas or round and green peas Each parent donates two alleles to the offspring

Phenotypes - Dihybrid Crosses RRYY, RRYy, RrYY, RrYy = Round Yellow rrYY, rrYy = Wrinkled Yellow RRyy, Rryy = Round Green rryy = Wrinkled Green

Incomplete Dominance The heterozygote is an intermediate form of both alleles for a trait. Example: Cross red (RR) flower with a white (WW) flower. The resulting RW flower is pink.

Codominance Both alleles are expressed equally. Notation is B and W instead of B and b. B for black, W for white BB black, BW white and black, WW white. Ex: cows, chickens

Multiple Alleles More than 2 alleles exist for any one gene or trait. The result is various expressions of the gene. Example: various hair colors in mice.

Only two alleles are found in an individual, but there can be many different alleles that exist in a population. Ex Blood type A,B, or O are all alleles AB=type, AO=Type A, BO= Type B OO = Type O You can not have ABO blood type because you only inherit two alleles.

Polygenic Inheritance Polygenic Inheritance: The inheritance pattern of a trait that is controlled by more than one gene. Genes may be on the same chromosome or different chromosomes. Ex. Skin color, eye color Very often, the more dominant alleles that are involved, the more the trait is expressed. Ex. 1 dominant allele: light skin, 2: darker, 4: very dark, etc.

Sex Linked Traits Humans have 22 pairs of autosomes, or chromosome pairs that resemble one another. The 23rd pair of chromosomes are called the sex chromosomes. Sex Linked Traits: Traits controlled by alleles that are found on the sex chromosomes, usually on the X chromosome. Ex. Color blindness, hemophilia (See p. 338). Notation is XBXb or XBXB (female) and XBY or XbY (male) instead of BB, Bb or bb. Can a man pass on a sex linked trait to his son?? Show work.

Mitosis Review Mitosis produces cells with exactly the same amount of chromosomes as the original cell. If this was the only means of cell division, offspring would end up with twice as many chromosomes as the parents.

Meiosis Important Terms Haploid: cell with one of each kind of chromosome (n) Organisms produce gametes that are haploid…egg and sperm Diploid: cell with two of each kind of chromosome (2n) Body cells of animals/plants have chromosomes that occur in pairs…one from each parent How do organisms produce haploid gametes? To produce haploid gametes, organisms under go meiosis

Meiosis Meiosis has 2 separate divisions…Meiosis I and Meiosis II Meiosis I begins with a Diploid cell…2n Meiosis II finishes with 4 Haploid cells (1n) These 4 Haploid cells are Gametes (Egg or Sperm) With Fertilization, Sperm has (23) chromosomes and Egg (23).. Haploid…come together to produce a Zygote with (46) chromosomes..Diploid This pattern of reproduction that involves the combining (fusion) of haploid gametes is called Sexual Reproduction

Meiosis QUESTIONS/EXAMPLES TITLE: Where do you find homologous chromosomes? in Diploid Cells Ex: Homologous Chromosomes: Paired chromosomes, each with genes for the same traits. These exist in Diploid cells and are what determine how an individual looks. Mom’s chromosomes for hair color Dad’s chromosomes for hair color

Phases of Meiosis

What happens within the cell during Interphase of Meiosis? DNA is Replication

Meiosis I

Crossing Over can occur Prophase I Crossing Over can occur Each pair of homologous chromosomes come together to form a four-part structure called a Tetrad

Metaphase I homologus pairs In Meiosis, the Tetrad of homologous chromosomes lines up down the middle

Anaphase I What gets separated during Anaphase I? Spindle fibers pull homologous chromosomes toward opposite ends of the cell Homologus pairs

Telophase I Are the two cells identical? No, the cells have different sets of chromosomes! Cells begin to separate into two cells

Meiosis I

Meiosis II Meiosis II is identical to Mitosis

Prophase II Nuclear Membrane breaks down, chromosomes condense. Chromosomes do not replicate during Prophase II of Meiosis.

Metaphase II Chromosomes line up down the center of the cell

Anaphase II Sister Chromatids separate towards opposite ends of each cell

Telophase II A nuclear envelope forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells. Produces 4 Haploid Cells that are genetically different How many and what type of cells are produced at the end of Telophase II? 4 haploid cells!!

Meiosis II

Mitosis vs. Meiosis Results in 2 genetically identical cells Cells are diploid Results in 4 genetically different cells Cells are haploid

Meiosis causes Genetic Variation Meiosis “shuffles” chromosomes so that the offspring are not identical to the parents Principle of Independent Assortment: genes for different traits segregate INDEPENDENTLY during meiosis, as long as they are on separate chromosomes.

HOW do genes for different traits separate independently? Answer: By chromosomes lining up randomly during meiosis.

Crossing Over – an exchange of genetic material between homologous chromosomes Occurs randomly anywhere on the chromosomes

Genetic Recombination= re-assortment of chromosomes and genetic information they carry, either by crossing over or independent segregation of homologous chromosomes

What does crossing over and independent assortment create? -Genetic Variation/offspring that are different from their parents. How does genetic recombination occur? -By independent segregation/assortment or crossing over

Genetic Mistakes Nondisjuction: chromosomes fail to separate correctly during meiosis Both chromosomes from a homologous pair move to the same pole of the cell Trisomy: zygote has an extra chromosome Ex: Trisomy 21 (Down Syndromes) Karyotype

What occurs when both chromosomes from a homologous pair are pulled to the same pole of the cell? Nondisjunction or genetic mistake

Genetic Mistakes Monosomy: A form of nondisjuction where zygote is missing one chromosome In humans, most zygotes/organisms with monosomy do not survive What is one example of Monosomy where organisms can survive? Ex: Turner Syndrome= Human females with only one X chromosome

Genetic Mistakes Nondisjuction of homologous chromosomes - Complete Diploid set of chromosomes is passed to gamete Offspring has 3 sets of that chromosome after fertilization Called: Triploid

Polyploids: Organisms with more than 2 sets of chromosomes - Rare in animals and usually causes death - Occurs frequently in plants Flowers/fruits are larger and usually healthier

Gene Linkage Genes close together on a chromosome are less likely to separate through crossing over. Gene linked Ex. Blonde hair and blue eyes. These genes are usually inherited traits together It is the chromosomes that separate independently not genes.

The law of independent assortment Chapter 11 Concept Map Heredity Genetics Traits Gregor Mendel Gametes Pollination Fertilization 1st Generation 2nd Generation Alleles Dominant Recessive The law of segregation Phenotype Homozygous Genotype Heterozygous The law of independent assortment

Chapter 11 Concept Map Reginald Punnett Punnett Square Monohybrid cross Dihybrid Cross Genes, Chromosomes and numbers Haploid Cell Diploid Cell Homologous chromosome Heredity Phases of Meiosis 1 & 2 Interphase Prophase I & II Metaphase I & II Anaphase I & II Telophase I & II