Presentation on theme: "Genetics: The Science of Heredity"— Presentation transcript:
1Genetics: The Science of Heredity Lesson 1A Priest-ScientistGregor Mendel
2Who was Gregor Mendel? Gregor Mendel was an Austrian monk. He lived between 1822 to 1884.He was a teacher & a botonistHe did experiments on hundreds of pea plants.Why Pea Plants?Simple genetic make upTraits are easily observedCan cross-pollinate or self-pollinate
3Heredity Father of Genetics Mendel’s work with pea plants has become the basis of genetics, the study of heredity.Heredity is the passing of traits from parents to offspring.
4Mendel’s Pea Experiments He crossed plants with two different traits, for example purple flowers with white flowers.He started his experiments with purebred plants known as True Breeders.Purebred plants ALWAYS produce offspring with the same trait as the parent. For example, if the parent is tall, all offspring will be tall. If the parent is short, all offspring will be short.
6F1 Generation Mendel called the parent plants the P generation. He called the offspring from the parents the F1 generation.F is from the Latin word, filial, which means son.When Mendel crossed pure pea plants with purple flowers with pure pea plants with white flowers, all the F1 generation had purple flowers.P Generation (Parent Plants)F1 Generation, Offspring of the Parent Plants
7F2 GenerationWhen he crossed the F1 generation peas with one another, only some of the offspring had purple flowers. These formed the F2 generation.Mendel found that in the F2 generation, ¾ of the plants had purple flowers and ¼ of them had white flowers (3:1 ratio).F1 Generation, offspring of Parent PlantsF2 Generation, offspring of F1 Generation
8Lesson 1 Review 1. Who was Gregory Mendel? 2. Why did he choose peas for his experiments?3. What is heredity?4. What is genetics?5. What is a purebred plants?6. What is the P generation?7. What is the F1 generation?8. What is the F2 generation?
10Dominant and Recessive Traits It seemed to Mendel, that for each characteristic in peas, one trait was stronger than the other.He called the “stronger” one, the dominant trait.He called the “hidden” one, the recessive trait.This has become known as “Mendel’s Principle of Dominance”
11Genes and AllelesThe traits of peas (and yours) are controlled by factors that scientists call genes.You inherit your genes from your parents.The different forms of a gene are called alleles.You inherit a combination of two alleles from your parents.
12Dominant and Recessive Traits in Peas For each of the 7 traits that Mendel studied in peas, there is a dominant allele and a recessive allele.If a plant inherits both a dominant allele and a recessive allele, the dominant allele masks the recessive allele.
13Understanding Mendel’s Experiments Part I 2 alleles for purplePP1 allele for purple. 1 allele for whitePp2 alleles for whitepp
14Understanding Mendel’s Experiment Part II 1 allele for purple 1 allele for whitePpPp2 alleles for purplePP2 alleles for whitepp1 allele for purple 1 allele for whitePp
15Principle of Segregation Based on the outcome of his experiment, Mendel developed his “Principle of Segregation” that states that when forming sex cells, the paired alleles separate so that each egg or sperm only carries one form of the allele.The two forms of the allele come together again during fertilization.
16Lesson 2 Review16. What did Mendel find to be the same with all 7 traits of the pea plant that he studied?17. What are genes?18. What are dominant alleles?19. What are recessive alleles?20.What happens if a pea plant inherits two dominant allele of the same gene?21. What happens if a pea plant inherits a dominant allele and a recessive allele of the same gene?22. What happens if the pea plant inherits two recessive alleles of the same gene?
17Probability and Genetics Lesson 3Probability and Genetics
18ProbabilityProbability is the likelihood that a particular event will occur.The laws of probability determine what is likely to occur, not what does occur.Mendel was the first scientist that applied the principles of probability to genetics.
19Punnett SquarePunnett square is a table that shows all the possible combinations of alleles that can result when two organisms cross.Using Punnett square, geneticists can predict the probability of occurrence of a particular trait.The allele that each parent will pass to its offspring is based on chance, just like tossing a coin.
20Genotypes and Phenotypes Genotype: Indicates the alleles that the organism has inherited regarding a particular trait.Phenotype: The actual visible trait of the organism.Genotype
21Homozygous and Heterozygous Homozygous: An organism with two identical alleles for a trait (a purebred organism).Heterozygous: An organism that has two different alleles for a trait (a hybrid organism).
22Review 16. What it probability? How is it related to genetics? 17. What is the Punnett Square? How is it helpful to geneticist?18. What is a genotype?19. What is a phenotype?20. What is a homozygous organism?21. What is a heterozygous organism?
24Genetics Alleles 1. Alternative forms of genes. 2. Homozygous alleles are exactly the same.3. Dominant alleles – capitalized(TT - tall pea plants)a. Homozygous dominant4. Recessive alleles - lowercase(tt - dwarf pea plants)a. Homozygous recessive5. Heterozygous (different) (Tt - tall pea plants)
25Phenotype Outward appearance Physical characteristics Examples: 1. tall pea plant2. dwarf pea plant
26Genotype Arrangement of genes that produces the phenotype Example: 1. tall pea plantTT = tall (homozygous dominant)2. dwarf pea planttt = dwarf (homozygous recessive)3. tall pea plantTt = tall (heterozygous)
27Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.
28Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.1. What is the genotype of a homozygous tall plant?
29Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.2. What is the genotype of a homozygous short plant?
30Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.3. What is the genotype of a heterozygous tall plant?
31Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.4. A plant has a genotype of Tt. What is its phenotype?
32Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.5. A plant has a genotype of tt, what is its phenotype?
33Practice! Practice! Practice!!! In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.6. What are the two alleles for the height of a pea plant?
34Answers:1. TT2. tt3. Tt4. Tall5. short6. T (tall) and t (short)
36Monohybrid CrossA breeding experiment that tracks the inheritance of a single trait.Mendel’s “principle of segregation”pairs of genes separate during gamete formation (meiosis) & reform during ferlization.
37Homologous Chromosomes PaternalMaternaleye color locusB = brown eyeseye color locusb = blue eyesThis person would have brown eyes (Bb)
38Monohybrid CrossExample: Cross between two heterozygotes for brown eyes (Bb)BB = brown eyesBb = brown eyesbb = blue eyesBbBb x Bbmalegametesfemale gametes
39Monohybrid Cross B b Bb x Bb 1/4 = BB - brown eyed 1/4 = bb - blue eyed1:2:1 genotype3:1 phenotypeBBBbbb
40Practice! Practice! Practice!!!! In cocker spaniels black (B) is dominant to red (rust) (b).1. What would be the phenotypic ratio of a cross between a true breeding black crossed with a true-breeding rust?
41Step 2 – List the possible gametes from each parent BBbbBBbb
42Step 3 Draw punnett square and place the gametes on the sides. BBbbbbBBbbBB
43Step 4 Fill in the punnett square to find the possible zygotes BBbbbbBBbbBbBbBBbBBb
44Step 5 Determine the genotypic and Phenotypic ratios BBbbbbBBbbPhenotypeBbBbB100% BlackGenotypeBbBBb100% Bb
45Practice Problems Complete a Punnett Square for each of the following: T = tall plant t = short plantP = purple flowers p = white flowersPP x pp Pp x ppTt x TT 5. tt x TTPp x PP Tt x tt
46Lesson 6 Dihybrid CrossA breeding experiment that tracks the inheritance of two traits.Mendel’s “principle of independent assortment”a. during Metaphase I, each pair of alleles seperates independentlyb. formula: 2n (n = # of heterozygotes)
47Independent Assortment Question: How many gametes will be produced for the following allele arrangements?Remember: 2n (n = # of heterozygotes)1. RrYy2. AaBbCCDd3. MmNnOoPPQQRrssTtQq
48Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametesABCD ABCd AbCD AbCdaBCD aBCd abCD abCD3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes
49Dihybrid CrossExample: cross between round and yellow heterozygous pea seeds.R = roundr = wrinkledY = yellowy = greenRrYy x RrYyRY Ry rY ry x RY Ry rY rypossible gametes produced
53Incomplete DominanceF1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.Example: snapdragons (flower)red (RR) x white (rr)RR = red flowerrr = white flowerRr
54Incomplete Dominance R produces the Rr F1 generation r All Rr = pink (heterozygous pink)produces theF1 generationRr
55CodominanceIn codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other.Roan CowIs both white and red
57MUTATIONSMistakes that occur during the duplication of the chromatin materialGERM CELL MUTATIONS - occur in gametes, passed on to offspring without affecting parentSOMATIC MUTATIONS - occur in body cells, not usually passed on to offspring
58Mutations Chromosomal Mutations affect the entire chromosome Occur during the Crossing Over period of MeiosisDuplication Mutations – one chromosome carries two copies of a gene or set of genesDeletion Mutations – post cell division, the new cell will lack the genes that were carried by the piece that broke off
59Chromosomal Mutations, cont. Inversion Mutations – the segment that breaks off reattaches itself but in the backwards positionTranslocation Mutations – a chromosome segment attaches itself to a non-homologous chromosome
60Chromosome Mutations, cont. NONDISJUNCTION-failure of a chromosome to separate from its homologue during meiosis*one gamete will receive an extra copy of a chromosome while the other gamete will not have the chromosomeResults in: *DOWN SYNDROME (TRISOMY 21)-an extra copy of the 21st chromosome
61Mutations Gene Mutations affect individual genes on a chromosome. Occur by:Insertion of a nucleotideorDeletion of a nucleotide
62The Number of Chromosomes Humans that have even one missing or one extra chromosome usually die before birth or have serious defects.Down Syndrome happens when a person is born with an extra copy of chromosome number 21.
63Chromosomes Males are XY and females are XX Genes found on sex chromosomes…SEX LINKEDGenes on an X chromosome are X-LINKED. Genes on a Y chromosome are Y-LINKED.Eye color in fruit flies is X-Linked. Only male fruit flies have white eyes.
64Sex linked traits Examples of sex linked traits are 1. Blood clotting factor – this factor is located on the X chromosome and the dominant allele allows your blood to clot normally.The recessive form does not allow your blood to clot.Two recessive alleles causes the disease hemophilia.Boys are more likely to get the disease because they only have one X.
652. Red-green color vision is another sex-linked trait 2. Red-green color vision is another sex-linked trait. The dominant allele allows you to see reds and greens. The recessive allele prevents seeing red or green.Boys are most often affected because of having only 1 X chromosome.
67Sex Influenced Traits Influenced by male or female sex hormones Baldness
68Multiple AllelesTraits that are determined by 2 or more alleles & produce different colorations based on the original traits.Include:blood typeHair colorEye color
69Polygenic Traits The results of the interaction of multiple genes Example: hypertensionCaused by the interaction of one’s:WeightAbility to process fatsCholesterol countAbility to process saltsLifestyle - i.e. Smoking, drinking, exercise
70Mutagens Environmental factors that can cause mutations Include: Radiation exposure via X-rays or UV lightNatural or made-made chemicalsPollutantsExtremely high temperaturesViruses
71Human Karyotype showing homologous chromosome pairs This individual has inherited three copies of chromosome 21and has a condition called Down syndrome.
72Nondisjunction, cont.KLINEFELTER’S SYNDROME- (XXY)-feminine characteristics, mentally impaired, infertileTURNER’S SYNDROME- (XO)- female appearance, no sexual maturity, infertile
73Human Genetic Disorders Cystic fibrosis-(CF)-difficulties with breathing and digestionSickle cell anemia -forms sickle shaped RBCs because of a defective protein called hemoglobin, leads to lack of O2 & circulatory problems