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2 An Austrian monk who worked with pea plants
Provided the foundation for modern genetics Scientists understood that traits were inherited before they understood the mechanics of inheritance 2

3 Traits Traits are distinguishing characteristics that are inherited.

4 Genetics Genetics is the study of biological inheritance patterns and variations in organisms.

5 Mendel chose pea plants because they were quick to reproduce and he could control how they mated (model organisms)‏ What is a model organism? 5

6 Purebred pea plants Known to have one trait or another, no in betweens!!

7 Pea plant traits He chose 7 traits to follow due to their “either-or” characteristics; there were no intermediate features Pea shape, pea color, pod shape, pod color, plant height, flower color, and flower position


9 In genetics, the mating of two organisms is called a cross
The parents in a cross are called the P generation (parental generation)‏ The offspring of that generation are called the F1 (first filial generation)‏ When Mendel crossed purple flowered pea plants with white flowered pea plants, the F1 was all purple When 2 offspring from the F1 were crossed, the resulting plants were purple and white (75% purple and 25% white)‏ 3:1 ratio 9

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11 3 main conclusions from his work
(1) Demonstrated that traits are inherited as discrete units Explained why individual traits in the peas did not blend or dilute over successive generations 11

12 Law of segregation (2 & 3) Collectively called the “Law of Segregation” Organisms inherit 2 copies of each gene. Where do those 2 copies come from? Organisms donate only one copy of each gene in their gametes.

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14 A gene is a heritable factor that has a specific characteristic.
Each gene has a specific locus, or location on a pair of homologs. 14

15 Alleles Alleles are alternative forms of a gene
Such as round or wrinkled peas, yellow or green peas, or purple or white flowers

16 2 alleles for each gene Homozygous – two of the same alleles Heterozygous – two different alleles

17 Dominant allele – the allele that is expressed; usually represented by a capital letter
The letter “B” represents brown eyes  BB or Bb Homozygous dominant or heterozygous Recessive allele – the allele that is only expressed if the dominant allele is absent; usually represented by a lowercase letter The letter “b” represents blue eyes  bb Homozygous recessive Are dominant alleles “better” or “stronger” than recessive alleles? Why or why not? 17


19 The genome is all of the genetic material in an organism
In genetics, we often only focus on a single trait or a set of traits 1. Genotype 2. Phenotype 19

20 GENOTYPE The genotype refers to the genetic makeup of a set of genes (what you don't see)‏ Genes that code for flower color, such as PP or Pp

21 PHENOTYPE The phenotype refers to the physical characteristics/traits of the individual organism ( what you see)‏ Purple flowers

22 Because some alleles are dominant over others, two genotypes could produce the dominant phenotype
Brown hair  HH or Hh In order to express the recessive phenotype, the individual must also have the recessive genotype Blonde hair  hh There are many factors that play a part in making one allele dominant over another 22

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24 Deals with probability
Punnett Square – a grid system for predicting the possible genotypes that result from a cross Deals with probability The likelihood that a particular event will occur The alleles from the gametes of both parents are placed on the axes outside the grid while the possible genotypes of the offspring are inside the grid Because segregation and fertilization are random events, each combination of alleles is just as likely as the next 24

25 Crosses that examine the inheritance of only one specific trait
Flower color in peas: purple (P) is dominant to white (p)‏ Cross a purebred purple flower with a purebred white flower. Determine the genotypes & phenotypes of the F1 offspring. What % is purple? What % is white? Cross 2 of the F1 offspring together. Determine the genotypes & phenotypes of the F2 offspring. What % is purple? What % is white? What is the genotypic ratio? What is the phenotypic ratio? 25

26 Still using flower color…
From the F2, cross a heterozygous flower with a homozygous recessive flower. Determine the genotypes & phenotypes of the F3 offspring. What % is purple? What % is white? What is the phenotypic ratio? What is the genotypic ratio? Testcross – a cross between an organism of unknown genotype with an organism of the recessive genotype; allows scientists to determine if the organism of unknown genotype is homozygous dominant or heterozygous 26

27 Crosses involving two different traits-what size will your grid be?
One trait does not affect the presence of another; known as the “Law of Independent Assortment” Basically says that allele pairs separate independently during meiosis and are, therefore, inherited separately Flower color and plant height in peas; flower color is the same as before; tall plants (T) are dominant to dwarf plants (t)‏ Cross 2 organisms that are heterozygous for both traits. 27

28 FOIL TtPp x TtPp Do one parent at a time, and place all of the genotypes on one side of your 16 square box. First letter of each trait = Outside letter of each trait = Inside letter of each trait= Last letter of each trait = Now do the second parent in the same manner. What is the probability that the plants will be tall and purple? tall and white? Short and purple? Short and white?

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30 Practice Problems Dihybrid Cross – blue eyes and blonde hair are recessive Bbhh X bbHh Probability of offspring with Blue eyes and blonde hair? Brown eyes and brown hair?

31 Patterns of Inheritance

32 Mendel’s Principles Mendel came up with certain principles; keep these in mind with these new patterns of inheritance Inheritance of biological characteristics is determined by genes which are passed from parents to offspring Some form of a gene may be dominant or recessive Each individual has 2 copies of a gene which will segregate during gametogenesis (Law of Segregation) Alleles for different genes segregate independently from one another (Law of Independent Assortment)

33 Incomplete Dominance Cases that result in one allele not being completely dominant over another allele This means that the heterozygous phenotype is somewhere between the two homozygous phenotypes “Blending” of phenotypes Snapdragons exhibit incomplete dominance with flower color Red flowers are RR White flowers are WW When a RR snapdragon is crossed with a WW snapdragon, the offspring are RW Pink flowers are RW


35 Codominance Codominance - Cases in which both alleles contribute to the phenotype of the organism Neither allele is dominant over the other So, both phenotypes are expressed RED x WHITERED AND WHITE

36 Multiple alleles Multiple alleles – Cases in which genes have more than 2 alleles that code for a trait More than 2 alleles exist in a population, NOT in the individual Human blood types (ABO) are codominant and have multiple alleles

37 IAIA or IAi = Type A IAIB = Type AB IBIB or IBi = Type B ii = Type O

38 Practice Problem A homozygous type B woman marries a heterozygous Type A man. Show the punnett square, genotypes & phenotypes

39 Sex linked disorders Sex-linked genes are carried on the sex chromosomes Males- XY Females-XX Most traits are on the X-chromosome, which means that the female has to get two copies of the gene to show a genetic disorder. Males only have to get one copy of the bad gene. Some examples of sex linked genes are : baldness, colorblindness, hemophilia, Duchenne Muscular Dystrophy

40 Practice Problem Cross a white-eyed female fruit fly and red-eyed male (White eyes are X-linked, recessive)

41 Red-green colorblindness

42 Polygenic Traits Many traits are characterized by the interaction of several genes Human skin color is determined by the interaction of 6 separate genes Humans of the same race can have varying skin tones due to the interactions of the genes coding for skin color Human eye color is also determined by 3 separate genes Brown > green > blue Only determines the color of the eyes, not the varying in eyes of the same color (dark brown eyes vs. light brown eyes)

43 Epistasis A type of polygenic trait Albinism is epistatic
Certain alleles code for a trait, but other alleles on different genes can affect whether or not a phenotype is expressed Albinism is epistatic One allele blocks the others in pigment production if it is expressed Color of the coat in Labrador retrievers is a result of epistasis Black coat color (B) is dominant to brown coat color (b) Yellow coat color (e) is the recessive epistatic gene; meaning it will block out all other coat colors if it is present BBEE, BBEe, BbEE, & BbEe – black lab bbEE & bbEe – chocolate lab BBee, Bbee, & bbee – yellow lab


45 Practice Problems Incomplete Dominance
In northeast Kansas there is a creature known as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (RR) individual is red, and a heterozygous (RB) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?

46 Practice Problems Codominance
A cross between a black cat and a tan cat produces a tabby cat (black and tan fur) What percentage of cats will have tan fur if a black cat is crossed with a tabby cat? What percentage will have tabby fur if two tabby cats are crossed?

47 Practice Problems Blood Typing
A male who has AB blood marries a female with Type A blood. Their child has type B blood. What is the mom’s genotype? Use a Punnett Square to explain your answer. A male has type B blood and a female has type AB, if their child has type A, what is the dad’s genotype?

48 Practice Problems Sex-linked Traits
A female with hemophilia mates with a normal male. Create a Punnett Square. What is the probability they will have a male with hemophilia? A female? A female carrier of hemophilia mates with a male with hemophilia. Create a Punnett Square. What is the probability they will have a male with hemophilia? A female? If a male is a hemophilic, which parent gave him the defective allele?

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