Gregor Mendel • Gregor Mendel: – Austrian monk lived from 1822-1884 – Mendel developed principles of heredity without any knowledge of genes or chromosomes – His principles were established through experiments with pea plants Why was Mendel successful with the pea? • Used pure breeding, 7 contrasting traits • Studied characteristics one at a time for many generations • Used mathematics in analyzing his results • Obtained large numbers of offspring • Chose pea plants which normally self-fertilize • Inexpensive • Used scientific method • Easy to pollinate (transfer of male pollen to egg) Mendel’s 7 contrasting traits Genes and Heredity • Genes: factors that control organism traits – the part of chromosome that contains the genetic code • Every organism requires a set of coded instructions for specifying its traits • For offspring to resemble their parents, there must be a reliable way to transfer hereditary information from one generation to the next Genes and Heredity • Heredity the passing of traits from parents to offspring. • Genetics the study of heredity (the passing of traits) • Each human cell contains 30 thousand different genes Alleles • Alleles: part of a gene associated with a particular characteristic & located on a specific chromosome • Example: – Height is a gene(height is a trait) – tallness or shortness are alleles • The alleles determine how each gene is expressed. At least 2 alleles for one gene. T TT t t Chromosomes and Traits • chromosomes: hereditary units of an organism -carries genetic information -made of DNA -consists of two identical sister chromatids and a centromere. • locus: particular point where a certain gene is found on a chromosome cenrtomere Sister chromatids Homologous Chromosomes pair of associated chromosomes one from mom & one from dad - always the same size (EXCEPT XY) - centromere always in the same spot - genes on sister chromatids are identical - the alleles on homologous chromosomes are coded for the same gene, but could be different. Asexual vs. Sexual Reproduction • Asexual reproduction: – All the genes come from a single parent – These genes are normally identical to the parent (clone) • Sexual reproduction: – Organisms receive half their genetic information from the Mother's egg and half from their Father's sperm – Sexually reproduced offspring resemble but are not identical to their parents Back to Mendel • The significance of Mendel's work was not immediately recognized • Mendel's hereditary factors, now called genes, exist at definite loci on chromosomes • The gene-chromosome theory provides the mechanism to account for the hereditary patterns which Mendel observed Genetics Terms • homozygous (pure): the alleles on homologous chromosomes are the same • heterozygous: (hybrid): the alleles on homologous chromosomes are different • parental generation (P): the two original organisms being crossed - usually pure • first filial generation: the first generation of offspring from the parents • second filial generation: generation of offspring arising from the first filial generation Three Laws by Mendel 1. Law of Dominance: – a pattern of heredity in which one allele of a gene may express itself by masking the presence of the other allele – Example: red flower (RR) X white flower (rr) red flower (Rr) X Law of Dominance • Dominant Trait: the trait or allele that is expressed (capital letter) R • Recessive Trait: the trait or allele that is present but that is not expressed (lowercase letter) r Punnett Squares • Punnett square: a model used to predict the results of a genetic cross • Genotype: the genetic makeup of an organism – Homozygous Dominant: TT – Homozygous Recessive: tt – Heterozygous: Tt • Phenotype: the appearance of an organism – Describe what it looks like TT - Tall tt - short Tt - Tall Example of Dominance Problem: Cross homozygous dominant with homozygous recessive • R = red • r = white • RR x rr R r Results: 1st Generation Flowers: Phenotype: 100% red Genotype: 100% heterozygous r Rr Rr R Rr Rr 2. Law of Segregation Mendel’s second law – When gametes are formed during meiosis: • There is a random segregation of homologous chromosomes • Random segregation of sister chromatids & alleles • The result: new gene combinations are likely to be produced • Segregation means _______________ and can lead to genetic recombination. Example of Segregation Problem: Cross offspring from 1st cross (2 heterozygous parents) • R = red • r = white • Rr x Rr Results: 2nd Generation Flowers: Phenotype: 75% red, 25% white Genotype: 25% homozygous dominant, 25% homozygous recessive, 50% heterozygous R r R r RR Rr Rr rr Law of Independent Assortment Mendel’s third Law – Scenario: Two different traits located on two different chromosomes • They segregate randomly during meiosis • May be inherited independently of each other • The cross of two organisms heterozygous for a trait is known as a dihybrid cross Law of Independent Assortment Incomplete Inheritance • Two examples: – Incomplete Dominance – Codominance • Incomplete Dominance: – Case where one allele is partially dominant over the other – Examples: red X white snapdragons pink snapdragons cross between black and white Andulusian fowl gives blue (gray) fowl Example of Incomplete Problem: Cross offspring from 1st cross (2 heterozygous parents) • R = red • r = white • Rr x Rr R R RR r Rr Results: 2nd Generation Flowers: Phenotype: 50% pink, white 25%, 25% red Genotype: 50% heterozygous 25% homozygous dominant 25% homozygous recessive r Rr rr Intermediate Inheritance • Codominance: a case in which neither allele is dominant over the other – Alleles have equal power • Examples: – Cross between red and white short horned cattle gives roan cattle – Checkered black & white chicken – Sickle-cell Anemia - a blood disease where RBCs are sickle shaped or half moon. Most common African. – Heterozygous - half normal half sickle shape Example of Codominance Problem: Cross offspring from 1st cross (2 heterozygous parents) • R = red • r = white • Rr x Rr R R RR r Rr Results: 2nd Generation Flowers: Phenotype: 50% red & white 25% red, 25% white Genotype: 25% homozygous dominant 25% homozygous recessive 50% heterozygous r Rr rr Pink Snapdragons X Roan Cattle X Red Cattle Roan Cattle White Cattle Multiple alleles • Traits that are controlled by more than 2 alleles • Results in multiple phenotypes • Examples: – Pigeons BA dominant over B BA and B are dominant over b – Blood groups in humans Four blood types A B AB & O Dihybrid Cross Problem: Cross homozygous tall and homozygous wrinkled seeds with homozygous short and homozygous smooth seeds T = tall t = short Q = wrinkled q = smooth What are the genotypes for these plants? TTQQ x ttqq TTQQ x ttqq TQ TQ TQ TQ tq TtQq TtQq TtQq TtQq tq TtQq TtQq TtQq TtQq tq TtQq TtQq TtQq TtQq tq TtQq TtQq TtQq TtQq Phenotype: 100% Tall & Wrinkled Dihybrid Cross • What is the phenotype from this cross? – 100% Tall and Wrinkled • What is the genotype from this cross? – We don’t worry about genotype for dihybrid crosses Complete the following Dihybrid cross Step 1 - set up gamettes(sex cells) (1 3, 1 4, 2 3, 2 4) TtQq x TtQq Complete the following Dihybrid cross TtQq x TtQq TQ tq Tq tQ TQ TTQQ TTQq TtQQ TtQq Tq TTQq TTqq TtQq Ttqq tQ TtQQ TtQq ttQQ ttQq tq TtQq Ttqq ttQq ttqq What are the phenotypes for the above cross??? • 9 - Tall & Wrinkled • 3 - Tall & round • 3 - Short & wrinkled • 1 - Short & round Changing Chromosome Structure Translocation: transfer of one section of a chromosome Addition: a portion of one chromosome is attached to another chromosome Deletion: a portion of a chromosome is taken away from a chromosome Inversion: a portion of a chromosome breaks off and then becomes reattached to the same chromosome in an inverted (upside down) fashion Gene Expression • Influence of External Environment: • Examples: Temp., nutrition, light, chemicals – Color of rabbit in the summertime: brown – Color of rabbit in the winter: white – The temperature effects what color fur (or what proteins) are expressed – Temp also determines the sex of a gator – Light determines color of bacteria Gene Expression • Influence of Internal Environment: • Examples: Hormonal influences – Horn size in mountain sheep – Male pattern baldness – Peacock feathers Gene Expression • Influence of Internal Environment: • Examples: Hormonal influences – Horn size in mountain sheep – Male pattern baldness – Peacock feathers Problem 1 Phenotype of tt ------------------------- Short Genotype of tt--------------------------- Homozygous recessive Phenotype of TT ----------------------- Tall Genotype of TT------------------------- Homozygous dominant Phenotype of pure dominant-------- Tall Genotype of pure homozygous----- TT Phenotype of pure recessive-------- Short Genotype of pure recessive--------- tt Problem 2 Problem: A married couple want to know their chances of having girl X Y X XX XY X XX XY X __ Y x __ X __ X __ Results: 2nd Generation Flowers: Phenotype: 50% BOY, 50% GIRL Problem 3 Problem: Cross 2 heterozygous parents • R = red • r = white R R R __ r r x __ • _R_ __ r Results: 2nd Generation Flowers: Phenotype: 75% red, white 25% Genotype: 50% heterozygous 25% homozygous dominant 25% homozygous recessive r RR Rr Rr rr Problem 4: Law of dominance Pure dominant cross with hybrid • R = red • r = white R __ R x __ R __ r • __ R R RR r Rr Results: 2nd Generation Flowers: Phenotype: 100% red Genotype: 50% homozygous dominant 50% heterozygous R RR Rr Problem 5: Law of dominance Problem: The male’s genotype is heterozygous. The female is phenotypically dominant but does carry the recessive allele. • R = red • r = white r x _R _r •R _ _ R R RR r Rr r Rr rr Results: 2nd Generation Flowers: Phenotype: 75% red, white 25% Genotype: 50% heterozygous 25% homozygous dominant 25% homozygous recessive Problem 6: Law of Codominance Problem: Cross 2 heterozygous parents • R = red • r = white R r_ x _R _r • _ R R RR r Rr Results: 2nd Generation Flowers: Phenotype: 25% red, white 25% 50 % red & white Genotype: 25% homozygous dominant 25% homozygous recessive 50% heterozygous r Rr rr Nature vs. Nurture • In many cases it is not only the genes that we have that determine what we look like • Scenario: If identical twins (same DNA) were separated at birth and lived in 2 different environments and then brought together 25 years later would they look the same? Why or why not? Nature vs. Nurture • Answer: The identical twins would have similar features (eye color, size of nose, etc.) but may look very different. What they did throughout their lives effects what they look like – For example: sun exposure, diet, hygiene, injuries, etc. Polygenic Inheritance A pattern of a trait that is controlled by 2 or more genes.Phenotype express a range of variability. • Examples: – Stem length, human height, eye color & skin color Stem length for a totally recessive plant is____ cm. aabbcc = 4 cm Aabbcc = cm AAbbcc = cm AABbcc = cm AABBcc = AABBCc = AABBCC = cm cm cm Crossing Over • Crossing Over: during meiosis homologous chromosomes often: – Twist around each other and break then – Exchange segments and rejoin • Crossing over results in: – The rearrangement of genes – An increased variability of offspring Karyotypes • Karyotype: an enlarged photograph of the chromosomes in an organism Human Karyotype • Human diploid cells contain 23 pairs of chromosomes • Autosomes: body chromosomes (22 pr. in humans) • Homo sapiens have one pair of sex chromosomes – Males: each sex chromosome is unlike and is designated XY – Females: each sex chromosome is alike and is designated XX • The sex of a human is genetically determined at fertilization when a sperm cell containing either an X or a Y chromosome unites with an egg cell containing an X chromosome Fertilization Mutations • Mutation: change in DNA – Mutations in body cells effect present organism, but CAN NOT BE PASSED ON to offspring – Mutations in sex cells CAN be passed on to the offspring • WHY?: Nonsex cells are not apart of the fertilization process—only sex cells are Mutations • Chromosomal Alterations: – Nondisjunction • Example: Down’s Syndrome – Polyploidy • Example: 3n or 4n set of chromosomes • Most mutations are harmful and recessive Mutagenic Agents • Mutagenic Agents: increase the possibility of mutations – Radiation: X-rays, ultraviolet, radioactive & substances – Chemicals: formaldehyde, asbestos, and nicotine • The adaptive value of a gene mutation is dependent upon the nature of the mutation and the type of environment with which the organism interacts Genes and the environment • The environment interacts with genes in the development and expression of inherited traits • Here is an example… Types of Selective Breeding • Artificial Selection: individuals with desirable traits are mated to produce offspring with those traits • Inbreeding: offspring produced by artificial selection are mated with one another to reinforce those desirable traits Selective Breeding • Hybridization: crossing two individuals with different desirable traits to produce offspring with a combination of both desirable traits – English shorthorn cattle (good beef) X Brahman cattle (heat resistant) Santa Gertrudis cattle (good beef and heat resistance) Types of Selective Breeding • Mutations may be preserved by vegetative propagation – Example: seedless oranges and bananas Types of Selective Breeding • Recombinant DNA: – Also called genetic engineering – Creates new varieties of plants and animals by manipulating the genetic instructions of these organisms to produce new characteristics Genetic Research • Knowledge of genetics is making possible new fields of health care • Mapping of genetic instructions in cells makes it possible to detect, and perhaps correct, defective genes that may lead to poor health. • Substances from genetically engineered organisms may reduce the cost and side effects of replacing missing body chemicals. Genetic Research • Cloning: producing a group of genetically identical offspring from the cells of an organism • This technique shows great promise in agriculture – Plants with desirable qualities can be rapidly produced from the cells of a single plant Genetic Research • Genetic engineering: (recombinant DNA) – transfer of genetic information from one organism to another – includes the transfer of entire genes and gene splicing – Genetic engineering can correct genetic defects & produce agriculturally more efficient plants and animals Recombinant DNA • A cell can synthesize a new chemical coded for by its new genes • Examples: – Interferon: helps fight infections – Insulin: combat diabetes – Growth hormone: help stimulate growth Recombinant DNA X (X) How Recombinant DNA Works • Restriction Enzymes: enzymes used to cut segments of DNA in one organism so they can be transferred into another organism – Characteristics produced by the segments of DNA may be expressed when these segments are inserted into new organisms such as bacteria. – Inserting, deleting, or altering DNA segments can alter genes. An altered gene may be passed on to every cell that develops from it. Difficulties with Genetic Engineering • • • • The moved gene may not be expressed It is difficult to isolate the gene The trait may be recessive There may be unintended adverse qualities Human Genome Project • Human Genome Project: has allowed humans to know the basic framework of their genetic code – Knowledge of genetics is making possible new fields of health care – Genetic mapping is making it possible to detect and possibly correct, defective genes that may lead to poor health. More on Genetic Research • A down side to this is that health insurance agencies and other organizations may use this genetic information against individuals. • Substances from genetically engineered organisms may reduce the cost and side effects of replacing body chemicals. Human insulin produced in bacteria is already an example of this. Future of Genetic Engineering? Genetic Disorder Name of Technique used to Characteristic Disorder Diagnose of Disorder Sickle Cell Microscopic Low oxygen Anemia examination of blood supply of cells Down’s Karyotype Syndrome Mental Retardation PKU Mental retardation Urine analysis Amniocentesis • One final way to check for genetic diseases is through amniocentesis – Checks the proteins of the developing fetus while in the womb