Presentation on theme: "FUNDAMENTALS OF GENETICS"— Presentation transcript:
1FUNDAMENTALS OF GENETICS Modern BiologyChapter 9Pages
2Fundamentals of Genetics Objectives:Describe how Mendel’s results can be explained by the scientific knowledge of genes and chromosomes.Differentiate between a monohybrid cross and a dihybrid cross.Predict & perform results of monohybrid and dihybrid crosses
3Corkscrew tails can be traced back to one of the original American bulldogs used to develop the boston terrier breed.
5Do Now What is the genetic code? What molecule carries What is genetics?Genetic code - The genetic code is a set of instructions for transferring genetic data stored in the form of DNA or RNA into proteins. Proteins are integral to almost all of the biological processes that occur in living things. They are made up of amino acid sequences, and amino acids are produced based on the sequence of the genetic code.DNA carries the genetic code – RNA translates it.Genetics – field of biology dedicated to understanding how characteristics are transmitted from parents to offspring.
6K – W - L What do you know about inheritance? What do you want to know about inheritance?What have you learned about inheritance?
7Fundamentals of Genetics All of your characteristics or traits are unique to you.Parents may pass many of their own traits to their children, or offspring.For example, the color of your hair, the size of your feet and the shape of your nose are some ofyour traits.
8Fundamentals of Genetics The passing of these traits from parents to offspring is called heredity.The study of heredity is called genetics.Biologists who studyheredity are calledGeneticists.
9Fundamentals of Genetics Look at the photographs to the right.What traits have these babies inherited from their parent?
10Gregor Mendel The Father of Genetics rpee Seeds and Plants Home> Vegetables > Peas > Pea, Easy PeasyGregor Mendel The Father of GeneticsGenetics was founded with the works of an Austrian Monk, scientists and mathematician Gregor Johann Mendel.He experimented with garden pea plants.One of the first people to study genetics was an Austrian monk and scientist, named Gregor Mendel. In the late 1800’s Mendel began studying the passing of traits from parents to offspring.He, too wanted to know why certain patterns of traits showed up in living things.Mendel knew nothing about chromosomes, genes, or DNA
11Gregor MendelHis task of tending the garden gave him time to observe the passing of traits from parentpea plants to their offspring.He became interested in whycertain patterns oftraits showed upin living things.
12Mendel began his experiments by collecting seeds from his pea plants, carefully recording the traits of each plant.Seeds from tall plants usually produced tall plants but sometimes produced short plants.Seeds from short plants only produced short plants.…but, “WHY?”
13Mendel’s ExperimentsHe studied 7 different characteristics in his pea plants, each with 2 contrasting traits.CHARACTERISTIC-a distinguishing quality that an organism exhibits.Ex: height, hair color, eye color, skin color.TRAIT- specific hereditary options available for each characteristic.Ex: tall height/short height, smooth/blonde hair, brown/blue eyes,Dark/light skin.
14Inflated vs. Constricted CHARACTERISTICSTRAIT1. Plant HeightTall vs. Short2. Seed ColorYellow vs. Green3. Seed ShapeRound vs. Wrinkled4. Pod ColorGreen vs. Yellow5. Pod/Flower LocationAxial vs. Terminal6. Pod ShapeInflated vs. Constricted7. Flower ColorPurple vs. White
15Mendel’s MethodsHe decided to grow plants that were purebred - having a trait that will always be passed to the next generationThe term strain denotes all plants that are pure for a trait.
16Mendel Controlled Pollination He produced 14 strains (one for each of the 14 traits he observed) by allowing the plants to self-pollinate for several generationsThis became his Parent generation or his“P1 Generation”Mendel conducted his experiments with pea plants because they grow quickly and there are a lot of different kinds of pea plants.
17Mendel Controlled Pollination Pollination-transfer of pollen from anther (male flower part) to stigma (female flower part)Self–Pollination – occurs on same plantCross Pollination – occurs between different plants
18Mendel’s MethodsThen, Mendel cross pollinated plants that had contrasting traits to see what the offspring would look like. (P1 X P1- i.e. pure tall x pure short)Would the offspring (F1 Generation – offspring of P1) be tall, short, or medium ?Cross-pollination happens when pollen from one plant is transferred to the reproductive structure of another plant. The parent plants will produce a new plant. Cross-pollination happens in nature all the time.It can happen when an insect sits on a flower and pollen sticks to the insect.
19Mendel’s ResultsIn his first crosses, Mendel found that only one of the two traits appeared in the offspring plants –(F1 generation).For example, when he crossbred tall pea plants with short pea plants, the offspring (F1) were always tall.F1 – the first generation that result from cross between P1, P2.These plants are called the parent generation or P1.Their offspring are called first-generation plants, or F1. In Mendel's experiment, all of the first-generation plants were tall.
20After his first crosses, Mendel took those offspring plants (F1) and crossed them. In these second crosses, both traits showed up again in the F2 generation.(F2 GENERATION-offspring of crosses between the F1 generation).He observed that ¾ of the plants had the same trait as the F1 generation.
21This happened with every set of traits that Mendel studied. The same results happened in every experiment. One trait, like being tall, was always there in the first generation (F1).The other trait, like being short, seemed to go away; only to reappear again in the second generation (F2).This happened with every set of traits that Mendel studied.
22EXAMPLES:Plant Height CrossSeed Color CrossSeed Shape CrossParentP1 x P1Tall x ShortAll Tall PlantsTall x Tall¾ Tall¼ ShortYellow x GreenAll Yellow PlantsYellow x Yellow¾ Yellow¼ GreenRound vs. WrinkledAll Round PlantsRound X Round¾ Round¼ WrinkledFirst GenerationF1 x F1Second GenerationF2
23He called these controls “factors” Mendel hypothesized that something in the pea plants was controlling the characteristics that came throughHe called these controls “factors”(We now know that these factors are really traits controlled by Genes)
24Because each characteristic had two forms, he said there must be a pair of “factors” controlling each trait.Each pair consists of alternate forms (we now call alleles) of the same trait; one from mother and one from father.
25MENDEL’S 3 CONCLUSIONS: Based on his findings, Mendel formulated three laws or principles of heredity:1. Principle of Dominant and Recessiveness2. Principle of Segregation3. Principle of Independent Assortment
26Principle of Dominant & Recessiveness Through crossing thousands of pea plants, he was able to conclude that that both of these factors (alleles) together controlled the expression of a trait.Dominant traits were controlled by dominant alleles and recessive traits were controlled byrecessive alleles.Genes are the different parts of the DNA that decide the genetic traits a person is going to have. Alleles are the different sequences on the DNA-they determine a single characteristic in an individual. Another important difference between the two is that alleles occur in pairs. They are also differentiated into recessive and dominant categories. Genes do not have any such differentiation.
27Principle of Dominant & Recessiveness DOMINANT-can mask or dominate the other ‘factor’ and is displayed most often.RECESSIVE-the ‘factor’ that can be covered up; is displayed less often.Ex: the ‘factor’ (allele) for tall is dominant over the ‘factor’ (allele) for short, so the short allele would be the recessive allele.
28Principle of Dominant & Recessiveness Letters are used to represent the alleles that carry the trait found on genesIf the gene that controls the trait is dominant, the letter is written in uppercase.If the gene is recessive, the letter is written in lowercase.i.e. T- represents a dominant trait for tallness; t – represents a recessive trait for lack of tallness, or shortness
29T – dominant allele for tallness t – recessive allele for lack of tallness or shortness.W – dominant allele for round or smooth seedsw – recessive allele for wrinkled seedsP – dominant for flower color (purple)p – recessive allele for white flower
30Vocabulary ReviewGENE- a segment of DNA that codes for a specific characteristic.Ex: heightALLELE-the different forms of a gene (Mendel’s “factor”)Ex: allele for brown eyes is B/ allele for blue eyes is bSO…if BB is a brown eyed person and bb is a blue eyed person, what color eyes does someone with Bb have?
31Principle of Segregation Each parent has two factors (copies of each trait) and they segregate, or separate into different sex cells (gametes)Each gametegets only 1 factor (allele)of each trait
33Principle of Independent Assortment Mendel also crossed plants that differed in 2 characteristics, such as flower height and flower color.The data from these crosses showed that dominant traits do not always appear togetherttP?
34Principle of Independent Assortment The alleles for different genes on different chromosomes are not connected.The alleles for different traits are distributed into gametes independently (randomly) from each other.
35Principle of Independent Assortment Blue-eyed blonde Nmachi, whose name means “Beauty of God” in the Nigerian couple’s homeland, has baffled genetics experts because neither Ben nor wife Angela have ANY mixed-race family history.Pale genes skipping generations before cropping up again could have explained the baby’s appearance.
36Mendel’s law of independent assortment is supported by the fact that chromosomes segregate independently to gametes during meiosis.
37Gregor Mendel and his pea plants experiments (1857-1865)
38Do Now Who is the father of genetics? What type of organism did he work with?What are dominant and recessive traits?
39Vocabulary Review Chromosomes – made of DNA Gene – segment of DNA that controls a specific hereditary trait.Because chromosomes occur in pairs, genes occur in pairsAllele - (Mendel’s “factor”) – contrasting form of a geneDominant allele – capital letterRecessive allele – lowercase letterMost of Mendel’s findings agree with what biologists now know about molecular genetics – the study of the structure nad function of chromososmes and genes.
40AFTER MENDELToday, Geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses.Why would geneticists want to predict the probable genetic make up and appearance of offspring resulting from specified crosses?
41GENOTYPE & PHENOTYPEGENOTYPE-the genetic makeup of an organism (the combination of alleles an organism inherits).Use 2 letters together to represent genotype.PHENOTYPE-the trait displayed based on the genotype.Ex: BB – Brown eyesbb – Blue eyesBb – Brown eyes
44GENOTYPE & PHENOTYPEOrganisms with different genotypes may have the same phenotype.For example, a brown-eyed organism (BB) and a brown eyed organism (Bb) have different genotypes.However, they have the same phenotype, which is brown eyes
45Brown AllelesBrown AllelesBbBBOne pair of chromosomesfor eye colorOne pair of chromosomesfor eye color
47GENOTYPE & PHENOTYPEHOMOZYGOUS- organism has 2 of the same alleles for a trait.Homozygous Dominant-has 2 dominant alleles; dominant trait is displayedEx: BB = Brown-eyed organismHomozygous Recessive-has 2 recessive alleles; recessive trait is displayedEx: bb = blue-eyedHETEROZYGOUS-organism has 1 dominant and 1 recessive allele; the dominant trait is displayed.Ex: Bb = brown eyes
48Blue allelesBrown AlleleBlue AllelebbbBHomozygous –alleles are the sameHeterozygous –alleles are different
49Do Now What are Mendel’s Laws of Inheritance? What is an allele? What is homozygous vs. heterozygous?What is genotype vs. phenotype?
50ProbabilityIn order to understand genetics you need to have some basic concepts concerning probability.Probability – the likelihood that a specific event will occurCan be expressed as a decimal, percentage, ratio or fraction.P= number of times an event is expected to happennumber of opportunities for an event to happen
51ProbabilityIf you flip a coin once, what is the probability that it will land on heads? P(Event)= 1 (Heads) 2 (Heads or Tails) P= 1 2 ; .5; or 50%; 1:2 If you flip a coin twice, what is the probability that it will land on heads twice? P = 1 (Heads) 4 (Heads, Tails; Tails, Heads; Tails, Tails; Heads, Heads) P = ??Expected event – the one you are predicting or want to happenPossible outcome – how many different outcomes there are. (total number of times the event happens or can happen)
52Predicting the Results of Genetic Crosses Remember, probability is the likelihood that a chance event will occur.The value of studying genetics is in understanding how we can predict the likelihood of inheriting particular trait.The expected frequency of a particular event when an experiment is repeated an infinite number of times is the probability of the event. For a single coin toss, the probability of a head on a single toss is ½.Predicating the likelihood of a particular trait can help plant and animal breeders in developing varieties that have more desirable qualities. It can also help people explain and predict patterns of inheritance in family lines.His technique employs what we now call a Punnett square. This is a simple graphical way of discovering all of the potential combinations of genotypes that can occur in children, given the genotypes of their parents. It also shows us the odds of each of the offspring genotypes occurring.
53Predicting the Results of Genetic Crosses MONOHYBRID CROSS – a genetic cross between 2 individuals involving 1 pair of contrasting traits.
54Predicting the Results of Genetic Crosses One of the easiest ways to calculate the mathematical probability of inheriting aspecific trait wasinvented by an early 20thcentury English geneticist,Reginald Punnett .You can show probability as a percent by using this formula:Number of times an event occursx 100 = Probability %Number of total possible eventsFor example the probability for heterozygous tall (Tt) is:2 x 100 = 2 x 100 = 200 = 50 %Remember:200/4 is the same as 200 divided by 4.1 divided by 4 is the same as ¼The Punnett square also shows that there is a 25% chance (1/4 X 100) that the offspring will be homozygous tall (TT) or homozygous short (tt).
55Predicting the Results of Genetic Crosses His technique employs what we now call a Punnett square.A Punnett square is a chart that shows possible gene combinations of offspring of two parents whose genotypes are known.
56HOW TO DRAW A PUNNETT SQUARE 1. Write what each allele means.2. Write the genotypes of the parents.3. Draw a grid.4. Put the alleles for one parent along the top; put the alleles for the other parent along the side.5. Fill in the grid.
57EXAMPLE 1:HOMOZYGOUS X HOMOZYGOUS T= tall plant TALL X SHORTt = short plant (TT x tt)Genotype = 4 TtPhenotype = 4 tall plantsProbability = number of times an event(tall) is expected to happennumber of opportunities (total) for an event to happenProbability Ratio : 4/4 Probability percent: 100%TTTtTttTtTtTtt
58EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS T= tall plant TALL X SHORTt = short plant (Tt x tt)Genotype = 2 Tt, 2 ttPhenotype = 2 tall, 2 shortProbability = number of times an event(tall/short) is expected to happennumber of opportunities (total) for an event to happenProbability: 2/4 tall plants; 50% tall plants; 2:42/4 short plants; 50% short plants; 2:4TtTttttTtTtttt
59EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS T= tall plant TALL X TALLt = short plant (TT x Tt)Genotype = 2 TT, 2 TtPhenotype = 4 TallProbability = number of times an event(tall/short) is expected to happennumber of opportunities (total) for an event to happenProbability: 4/4 tall plants; 100% tall plants; 4:40% shortTTTTTTTTtTtTtt
60EXAMPLE 2:HETEROZYGOUS X HETEROZYGOUS T= tall plant TALL X TALLt = short plant (Tt x Tt)Genotype = 1 TT, 2 Tt, 1 ttPhenotype = 3 Tall, 1 shortProbability = number of times an event(tall/short) is expected to happennumber of opportunities (total) for an event to happenProbability: ¾ tall plants; 75%; 3:4¼ short plants; 25%; 1:4TtTTTTtTtTtttt
61TESTCROSSTESTCROSS - Cross to determine genotype of parent with dominant phenotype.Use to determine if the unknown is heterozygous or homozygous dominant genotype.Ex: A plant with green seed pods could have a genotype of GG or Gg.Cross the unknown parent with a homozygous recessive.
62T ? T t Tt T t ? t t Tt T t ? t Tt T= tall plant TALL X SHORT EXAMPLE 2: ? ? X HOMOZYGOUST= tall plant TALL X SHORTt = short plant (T? x tt)If Phenotype = 4 TallGenotype of Unknown = TTT?TTttT t? tTtTtT t? tt
63T ? t t Tt ? t t t t Tt ? t t t Tt T= tall plant TALL X SHORT EXAMPLE 2: ? ? X HOMOZYGOUST= tall plant TALL X SHORTt = short plant (T? x tt)If Phenotype = 3 Tall, 1 shortGenotype of Unknown = TtT?tTtt? tt tTtTt? tt tt
65More Complex Patterns of Heredity The way genes control traits can be complex and interact in different ways.
66All of these crosses we just did were examples of COMPLETE DOMINANCE. COMPLETE DOMINANCE-one allele is totally dominant over the other allele.EXAMPLE: PP and Pp = purple flower plants
67Incomplete DominanceWhen one gene for a certain trait is not completely dominant over the other gene, a blending effect occurs.INCOMPLETE DOMINANCE is a type of inheritance in which one allele (dominant) for a specific trait is not completely dominant over the other (recessive) allele. This results in a combined phenotype (expressed physical trait).
68Incomplete Dominance EXAMPLE: Four o’clocks (flowers) RR = red rr = white Rr = pinkRED (RR) X WHITE (rr)Genotype = 4RrPhenotype = 4 pinkRRrR rR rrR rR r
69Incomplete Dominance EXAMPLE: Four o’clocks (flowers) RR = red rr = white Rr = pinkPINK (Rr) X PINK (Rr)Genotype = 1 RR;2Rr;1rrPhenotype = 1 red, 2 pink, 1 whiteRrRR RR rrr rR r
70CodominanceAnother pattern of heredity can occur when two dominant genes are present for a certain trait.This pattern of heredity is called co-dominance (both variations of the gene appearing at the same time).Neither allele is dominant or recessive, nor do they blend.In the phenomenon of co-dominance, both dominant and recessive alleles lack their dominant and recessive relationships and both have capability to express themselves phenotypically
71Codominance EXAMPLE: roan horse: RR – red coat color R’R’ – white coat colorRR’ – roan coat – both red and white hairsGenotype = 4 RR’Phenotype = 4 RoanRRR’R R’R R’R’R R’R R’
72Codominance & Multiple Alleles Many traits are controlled by one gene that has more than two possible variations.These traits are controlled by multiple alleles.Human blood groups are controlled by multiple alleles.
73Codominance & Multiple Alleles There are 3 alleles for the gene that determines blood type. A, B, O(Remember: You have just 2 of the 3 in your genotype - 1 from mom & 1 from dad).With three alleles,we have a higher number ofpossible combinations increating a genotype.There are 6 differentgenotypes and four differentphenotypes blood type.
74IA IA IB IB Genotype = 4 IAIB Phenotype = 4 Blood Type AB Blood Type A (IAIA) X Blood Type B (IBIB)Genotype = 4 IAIBPhenotype = 4 Blood Type ABIAIAIBIAIBIAIBIBIAIBIAIB
76FYI The A and B alleles are equally dominant. A child who inherits and A allele from one parent and a B allele from the other parent will have type AB blood.What type of dominance is this?co-dominanceThe O allele is recessive to both A and B alleles. A child who inherits an A allele from one parent and an O allele from the other parent will have a genotype of AO and a phenotype of Type A blood.A child who inherits on O allele from one parentand an O allele from the other will have:Genotype?Phenotype?
77Predicting the Probability of a Dihybrid Crosses Cross between individuals studying one trait is Monohybrid CrossCross between individuals studying two traits is Dihybrid Cross
78Predicting the Probability of a Dihybrid Crosses A DIHYBRID CROSS is more complicated than monohybrid because there are more possible combinations.MONOHYBRID CROSS = 2 traits/4 possible offspringDIHYBRID CROSS = 4 Traits/ 16 possible offspring
79Predicting the Probability of a Dihybrid Crosses Example: AA or Aa = purple; aa = white BB or Bb = tall; bb = shortAaBb x AaBb (Purple Flower, Short Plant x Purple Flower, Short Plant)
80FYIOne really important thing that Mendel noticed from this type of cross was that traits (like flower color, height) are inherited independently - not together as a unit.This is type of cross helped Mendel develop the Law of Independent Assortment.REMEMBER - Law of Independent Assortment - Genes for various traits assort into gametes independently (due to homolouges lining up randomly at the metaphase plate.)
81Dihybrid Cross Example: Homozygous x HomozygousTall, Round Plant (TT RR) X Tall, Round Plant (TT RR)First, we need to determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.TTRRTR, TR, TR, TRTR, TR, TR, TR
83Dihybrid Cross Example: Heterozygous x HomozygousLET’S TRY IT !!Cross Tall, Round Plant (TtRr) X Short, Wrinkled Plant (ttrr)Determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.TtRrttrrTR, Tr, tR, trtr tr tr tr
85Dihybrid Cross Example: Heterozygous x HeterozygousCross Tall, Round Plant (TtRr) X Tall, Round Plant (TtRr)Determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.TtRrTR, Tr, tR, trTR Tr tR tr