Presentation on theme: "FUNDAMENTALS OF GENETICS Modern Biology Chapter 9 Pages 164 - 182."— Presentation transcript:
FUNDAMENTALS OF GENETICS Modern Biology Chapter 9 Pages
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 Fundamentals of Genetics
Do Now What is the genetic code? What molecule carries the genetic code? What is genetics?
K – W - L What do you know about inheritance? What do you want to know about inheritance? What have you learned about inheritance?
Fundamentals 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 of your traits.
heredity. The passing of these traits from parents to offspring is called heredity. genetics. The study of heredity is called genetics. Biologists who study heredity are called Geneticists. Fundamentals of Genetics
Look at the photographs to the right. What traits have these babies inherited from their parent?
Gregor Mendel The Father of Genetics Gregor Johann Mendel.Genetics was founded with the works of an Austrian Monk, scientists and mathematician Gregor Johann Mendel. He experimented with garden pea plants. rpee Seeds and Plants Homerpee Seeds and Plants Home> Vegetables > Peas > Pea, Easy PeasyVegetablesPeas
Gregor Mendel His task of tending the garden gave him time to observe the passing of traits from parent pea plants pea plants to their offspring. He became interested in why certain patterns of traits showed up in living things.
Mendel 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?”
He studied 7 different characteristics in his pea plants, each with 2 contrasting traits. –CHARACTERISTIC –CHARACTERISTIC-a distinguishing quality that an organism exhibits. Ex: height, hair color, eye color, skin color. –TRAIT –TRAIT- specific hereditary options available for each characteristic. Ex: tall height/short height, smooth/ blonde hair, brown/blue eyes, Dark/light skin. Mendel’s Experiments
CHARACTERISTICSTRAIT 1. Plant Height Tall vs. Short 2. Seed Color Yellow vs. Green 3. Seed Shape Round vs. Wrinkled 4. Pod Color Green vs. Yellow 5. Pod/Flower Location Axial vs. Terminal 6. Pod Shape Inflated vs. Constricted 7. Flower ColorPurple vs. White
purebredHe decided to grow plants that were purebred - having a trait that will always be passed to the next generation The term strain denotes all plants that are pure for a trait. Mendel’s Methods
He produced 14 strains (one for each of the 14 traits he observed) by allowing the plants to self-pollinate for several generations This became his Parent generation or his “P 1 Generation” “P 1 Generation” Mendel Controlled Pollination
Pollination-transfer of pollen from anther (male flower part) to stigma (female flower part) Self–Pollination – occurs on same plant Cross Pollination – occurs between different plants Mendel Controlled Pollination
cross pollinatedThen, Mendel cross pollinated plants that had contrasting traits to see what the offspring would look like. (P 1 X P 1 - i.e. pure tall x pure short) F 1 GenerationWould the offspring (F 1 Generation – offspring of P 1 ) be tall, short, or medium ? Mendel’s Methods
In his first crosses, Mendel found that only one of the two traits appeared in the offspring plants – (F 1 generation). (F 1 )For example, when he crossbred tall pea plants with short pea plants, the offspring (F 1 ) were always tall. Mendel’s Results
F1After his first crosses, Mendel took those offspring plants (F1) and crossed them. F2 generationIn these second crosses, both traits showed up again in the F2 generation. (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.
The same results happened in every experiment. One trait, like being tall, was always there in the first generation (F 1 ). The other trait, like being short, seemed to go away; only to reappear again in the second generation (F 2 ). This happened with every set of traits that Mendel studied.
EXAMPLES: Plant Height Cross Seed Color Cross Seed Shape Cross Parent P 1 x P 1 Tall x Short All Tall Plants Tall x Tall ¾ Tall ¼ Short Yellow x Green All Yellow Plants Yellow x Yellow ¾ Yellow ¼ Green Round vs. Wrinkled All Round Plants Round X Round ¾ Round ¼ Wrinkled First Generation F 1 x F 1 Second Generation F 2
Mendel hypothesized that something in the pea plants was controlling the characteristics that came through “factors”He called these controls “factors” Genes) (We now know that these factors are really traits controlled by Genes)
Because each characteristic had two forms, he said there must be a pair of “factors” controlling each trait. allelesEach pair consists of alternate forms (we now call alleles) of the same trait; one from mother and one from father.
MENDEL’S 3 CONCLUSIONS MENDEL’S 3 CONCLUSIONS : Based on his findings, Mendel formulated three laws or principles of heredity: 1. Principle of Dominant and Recessiveness 2. Principle of Segregation 3. Principle of Independent Assortment
(alleles 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 dominant alleles recessive traits Dominant traits were controlled by dominant alleles and recessive traits were controlled by recessive alleles. Principle of Dominant & Recessiveness
DOMINANT DOMINANT-can mask or dominate the other ‘factor’ and is displayed most often. RECESSIVE 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. Principle of Dominant & Recessiveness
Letters are used to represent the alleles that carry the trait found on genes If 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 Principle of Dominant & Recessiveness
T – dominant allele for tallness t – recessive allele for lack of tallness or shortness. W – dominant allele for round or smooth seeds w – recessive allele for wrinkled seeds P – dominant for flower color (purple) p – recessive allele for white flower
GENE GENE- a segment of DNA that codes for a specific characteristic. Ex: height ALLELE ALLELE-the different forms of a gene (Mendel’s “factor”) Ex: allele for brown eyes is B/ allele for blue eyes is b SO…if BB is a brown eyed person and bb is a blue eyed person, what color eyes does someone with Bb have? Vocabulary Review
Principle of Segregation Each parent has two factors (copies of each trait) and they segregate, or separate into different sex cells (gametes) Each gamete gets only 1 factor (allele) of each trait
Principle 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 together ttP?
Principle 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.
Principle of Independent Assortment
Gregor Mendel and his pea plants experiments ( )
Do Now Who is the father of genetics? What type of organism did he work with? What are dominant and recessive traits?
Vocabulary Review ChromosomesChromosomes – made of DNA GeneGene – segment of DNA that controls a specific hereditary trait. Because chromosomes occur in pairs, genes occur in pairs Allele -Allele - (Mendel’s “factor”) – contrasting form of a gene –Dominant allele – capital letter –Recessive allele – lowercase letter
AFTER MENDEL Today, 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?
GENOTYPE & PHENOTYPE GENOTYPEGENOTYPE-the genetic makeup of an organism (the combination of alleles an organism inherits). –Use 2 letters together to represent genotype. PHENOTYPEPHENOTYPE-the trait displayed based on the genotype. Ex: BB – Brown eyes –bb – Blue eyes –Bb – Brown eyes
bb Blue alleles Genotype Phenotype
Organisms 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 GENOTYPE & PHENOTYPE
b Brown Alleles One pair of chromosomes for eye color One pair of chromosomes for eye color B BB
HOMOZYGOUSHOMOZYGOUS- organism has 2 of the same alleles for a trait. Homozygous Dominant-has 2 dominant alleles; dominant trait is displayed –Ex: BB = Brown-eyed organism Homozygous Recessive-has 2 recessive alleles; recessive trait is displayed –Ex: bb = blue-eyed HETEROZYGOUSHETEROZYGOUS-organism has 1 dominant and 1 recessive allele; the dominant trait is displayed. –Ex: Bb = brown eyes GENOTYPE & PHENOTYPE
bb bB Blue Allele Brown AlleleBlue alleles Homozygous – alleles are the same Heterozygous – alleles are different
Do Now What are Mendel’s Laws of Inheritance? What is an allele? What is homozygous vs. heterozygous? What is genotype vs. phenotype?
Probability In order to understand genetics you need to have some basic concepts concerning probability. ProbabilityProbability – the likelihood that a specific event will occur Can be expressed as a decimal, percentage, ratio or fraction. P= number of times an event is expected to happen number of opportunities for an event to happen
Probability If you flip a coin once, what is the probability that it will land on heads? P(Event)= 1 (Heads) 2 (Heads or Tails) 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? P1 (Heads) P = 1 (Heads) 4 (Heads, Tails; Tails, Heads; Tails, Tails; Heads, Heads) P = ?? ¼
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. Predicting the Results of Genetic Crosses
MONOHYBRID CROSSMONOHYBRID CROSS – a genetic cross between 2 individuals involving 1 pair of contrasting traits. Predicting the Results of Genetic Crosses
One of the easiest ways to calculate the mathematical probability of inheriting a specific trait was invented by an early 20 th century English geneticist, Reginald Punnett. Predicting the Results of Genetic Crosses
Punnett square. His technique employs what we now call a Punnett square. Punnett square A Punnett square is a chart that shows possible gene combinations of offspring of two parents whose genotypes are known.
HOW 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.
EXAMPLE 1:HOMOZYGOUS X HOMOZYGOUS T= tall plantTALL X SHORT t = short plant (TT x tt) Genotype Genotype = 4 Tt Phenotype Phenotype = 4 tall plants Probability = number of times an event(tall) is expected to happen number of opportunities (total) for an event to happen Probability Ratio : 4/4Probability percent: 100% T Tt T t t
EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS T= tall plantTALL X SHORT t = short plant (Tt x tt) Genotype Genotype = 2 Tt, 2 tt Phenotype Phenotype = 2 tall, 2 short Probability = number of times an event(tall/short) is expected to happen number of opportunities (total) for an event to happen Probability: 2/4 tall plants; 50% tall plants; 2:4 2/4 short plants; 50% short plants; 2:4 T Tt t t t tt Tttt
EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS T= tall plantTALL X TALL t = short plant (TT x Tt) Genotype Genotype = 2 TT, 2 Tt Phenotype Phenotype = 4 Tall Probability = number of times an event(tall/short) is expected to happen number of opportunities (total) for an event to happen Probability: 4/4 tall plants; 100% tall plants; 4:4 0% short T Tt T T t TT Tt TT Tt
EXAMPLE 2: HETEROZYGOUS X HETEROZYGOUS T= tall plantTALL X TALL t = short plant (Tt x Tt) Genotype Genotype = 1 TT, 2 Tt, 1 tt Phenotype Phenotype = 3 Tall, 1 short Probability = number of times an event(tall/short) is expected to happen number of opportunities (total) for an event to happen Probability: ¾ tall plants; 75%; 3:4 ¼ short plants; 25%; 1:4 T Tt t T t TT Tt tt
TESTCROSS TESTCROSSTESTCROSS - 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.
EXAMPLE 2: ? ? X HOMOZYGOUS T= tall plantTALL X SHORT t = short plant (T? x tt) If Phenotype If Phenotype = 4 Tall Genotype of Unknown Genotype of Unknown = TT T Tt ? t t ? t T T t
EXAMPLE 2: ? ? X HOMOZYGOUS T= tall plantTALL X SHORT t = short plant (T? x tt) If Phenotype If Phenotype = 3 Tall, 1 short Genotype of Unknown Genotype of Unknown = Tt T Tt ? t t ? t t t t t
The way genes control traits can be complex and interact in different ways. More Complex Patterns of Heredity
COMPLETE DOMINANCEAll of these crosses we just did were examples of COMPLETE DOMINANCE. COMPLETE DOMINANCECOMPLETE DOMINANCE-one allele is totally dominant over the other allele. –EXAMPLE: PP and Pp = purple flower plants
When one gene for a certain trait is not completely dominant over the other gene, a blending effect occurs. INCOMPLETE DOMINANCE 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). Incomplete Dominance
R R r r R r EXAMPLE: Four o’clocks (flowers) RR = red rr = white Rr = pink RED (RR) X WHITE (rr) Genotype = 4Rr Phenotype = 4 pink
Incomplete Dominance R r r R R r R r EXAMPLE: Four o’clocks (flowers) RR = red rr = white Rr = pink PINK (Rr) X PINK (Rr) Genotype = 1 RR;2Rr;1rr Phenotype = 1 red, 2 pink, 1 white
Codominance Another pattern of heredity can occur when two dominant genes are present for a certain trait. co-dominance 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.
Codominance R R R’ R R’ EXAMPLE: roan horse: RR – red coat color R’R’ – white coat color RR’ – roan coat – both red and white hairs Genotype = 4 RR’ Phenotype = 4 Roan
Many traits are controlled by one gene that has more than two possible variations. multiple allelesThese traits are controlled by multiple alleles. Human blood groups are controlled by multiple alleles. Codominance & 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 of possible combinations in creating a genotype. There are 6 different genotypes and four different phenotypes blood type. Codominance & Multiple Alleles
Blood Type A (I A I A ) X Blood Type B (I B I B ) Genotype = 4 I A I B Phenotype = 4 Blood Type AB IAIA IBIB IBIB IAIA IAIBIAIB IAIBIAIB IAIBIAIB IAIBIAIB
Possible Blood Type Combinations
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-dominance The 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 parent and an O allele from the other will have: Genotype? Phenotype? FYI
Predicting the Probability of a Dihybrid Crosses Cross between individuals studying one trait is Monohybrid Cross Dihybrid CrossCross between individuals studying two traits is Dihybrid Cross
Predicting the Probability of a Dihybrid Crosses DIHYBRID CROSSA DIHYBRID CROSS is more complicated than monohybrid because there are more possible combinations. MONOHYBRID CROSSMONOHYBRID CROSS = 2 traits/4 possible offspring DIHYBRID CROSSDIHYBRID CROSS = 4 Traits/ 16 possible offspring
Predicting the Probability of a Dihybrid Crosses Example: AA or Aa = purple; aa = white BB or Bb = tall; bb = short AaBb x AaBb (Purple Flower, Short Plant x Purple Flower, Short Plant)
FYI One 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. Law of Independent AssortmentREMEMBER - Law of Independent Assortment - Genes for various traits assort into gametes independently (due to homolouges lining up randomly at the metaphase plate.)
Dihybrid Cross Example: Homozygous x Homozygous Tall, 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. TTRR TR, TR, TR, TR
Dihybrid Cross Example: Heterozygous x Homozygous LET’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. TtRr ttrr TR, Tr, tR, tr tr tr tr tr
Dihybrid Cross Example: Heterozygous x Heterozygous Cross 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. TtRr TR, Tr, tR, tr TR Tr tR tr