Presentation on theme: "Introduction to Mendelian Genetics"— Presentation transcript:
1 Introduction to Mendelian Genetics BiologyIntroduction to Mendelian Genetics
2 Genetics - The study of heredity, how traits are passed from parent to offspring orx=or
3 The study of heredity started with the work of Gregor Mendel and his pea plant gardenMendel was an Austrian Monk that livedin the mid 1800’s
4 Mendel’s Laws of Heredity Why we look the way we look...
5 What is heredity?The passing on of characteristics (traits) from parents to offspringGenetics is the study of heredity
6 Gregor MendelMendel used pea plants to discover the mechanism of heredity – how traits get passed from parents to offspring.
7 Mendel noted that the size of pea plants varied Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.
8 Why Mendel used peas... They reproduce sexually They have two distinct, male and female, sex cells called gametesTheir traits are easy to isolate
9 Mendel crossed the Plants Fertilization - the uniting of male and female gametesCross - combining gametes from parents with different traits
10 Questions What did Mendel cross? What are traits? What are gametes? What is fertilization?What is heredity?What is genetics?
11 What Did Mendel Find?He discovered different laws and rules that explain factors affecting heredity.
12 Phenotype & Genotype Phenotype - the way an organism looks Example - red hair or brown hairgenotype - the gene combination of an organismAA or Aa or aa
13 Heterozygous & Homozygous Heterozygous - if the two alleles for a trait are different (Aa)Homozygous - if the two alleles for a trait are the same (AA or aa)
14 Dihybrid vs Monohybrid Dihybrid Cross - crossing parents who differ in two traits (AAEE with aaee)Monohybrid Cross - crossing parents who differ in only one trait (AA with aa)
15 Questions... What is the phenotype? What is the genotype? What is homozygous?What is heterozygous?What is monohybrid crossing?
16 Mendel’s cross between tall pea plants yielded all tall pea plants Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants.Tall plants=XX=Short plants
17 Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. =x
18 Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x=
19 What Did Mendel Find?He discovered different laws and rules that explain factors affecting heredity.
20 Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information.
21 Carrying the information are chromosomes Chromosomes are made up of sections called genesGenes are made up of DNA
22 Rule of Unit Factors Each organism has two alleles for each trait Alleles - different forms of the same geneGenes - located on chromosomes, they control how an organism develops
32 ProbabilityThe likelihood that a particular event will occur is called_______.Probability
33 ProbabilityThe probability that a single coin flip will come up heads is…a. 100 percentb. 75 percentc. 50 percentd. 25 percent
34 ProbabilityThe probability that a single coin flip will come up heads is….a. 100 percentb. 75 percentc. 50 percentd. 25 percent
35 Probability Is the following sentence true or false? The past outcomes of coin flips greatly affect the outcomes of future coin flips.False
36 ProbabilityWhy can the principles of probability be used to predict the outcomes of genetic crosses?The way in which the alleles segregate is completely random, like a coin flip.
37 How do geneticists use Punnett squares? Punnett squares can be used to predict and compare the genetic variations that will result from a cross.
38 Genetics & Punnett Squares First let’s look at two basic kinds of genes:Dominant - A gene that is always expressed and hides othersRecessive - A gene that is only expressed when a dominant gene isn’t present
39 Dominant and Recessive Genes A dominant gene will always mask a recessive gene.A “widows peak” is dominant, not having a widows peak is recessive.If one parent contributes a gene for a widows peak, and the other parent doesn’t, the off-spring will have a widow’s peakWidows Peak
40 GeneticsPunnet Square - A tool we use for predicting the traits of an offspringLetters are used as symbols to designate genesCapital letters are used for dominant genesLower case letters are used for recessive genesGenes always exist in pairs
41 GeneticsA Widows Peak, dominant, would be symbolized with a capital “W”, while no widows peak, recessive, would be symbolized with alower case “w”.Father-No Widows Peak ‘w’Mother-Widows Peak ‘W’
42 GeneticsAll organisms have two copies of each gene, one contributed by the father, the other contributed by the mother.Homozygous - Two copies of the same geneHeterozygous - Two different genes
43 Genetics For the widows peak: WW - has a widows peak Homozygous dominantWw - has a widows peak Heterozygousww - no widows peak Homozygous recessive
44 Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww”Definitely Homozygous recessivewwEither HeterozygousWwor Homozygous dominantWW
45 GeneticsWe can use a “Punnet Square” to determine what pairs of genes Lilly hasA Punnet Square begins with a box 2 x 2One gene is called an “allele”One parents pair is split into alleles on top, the other along the sideEach allele is crossed with the other allele to predict the traits of the offspringAssume Lilly is heterozygousWwWwAssume Herman is homoozygous recessivewwwWwwwwWwww
46 GeneticsNotice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww”Half “Ww”, Heterozygous, and will have a widows peakHalf “ww”, Homozygous, and will not have a widows peakWwwWwwwwWwww
47 GeneticsAnother possibility is that Lilly might be “WW”, homozygous dominant.Notice that all the offspring are heterozygous and will have a widows peakAssume Lilly is homozygous dominantWWWWAssume Herman is homoozygouswwwWwWwwWwWw
48 GeneticsSo which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)?WwWWwWwwwwWwWwwWwwwwWwWw
49 If Lilly were heterozygous, then 1/2 of their offspring should have a widows peak, 1/2 shouldn’t If Lilly were homozygous, all of their children will have a widows peakWwWWwWwwwwWwWwwWwwwwWwWw
50 Recall that Herman and Lilly had another offspring, Marylin Recall that Herman and Lilly had another offspring, Marylin. She had no widows peak, therefore, Lilly must be heterozygous.
51 Genetics & Punnett Squares Now let’s look at two other basic kinds of genes, Incomplete dominance and Codominance:Incomplete dominance - Genes that work together to produce a third trait where the alleles are blendedLike a red flower crossed with a white flower produces a pink flower
52 Genetics & Punnett Squares Codominant - Genes that work together to produce a third trait where both alleles contribute to the traitLike a red flower crossed with a white flower produces a red and white flower
53 Genetics Hair color can be an example Prince Charming is blond Snow White has black hair
54 GeneticsWhat color hair will the offspring of Prince Charming and Snow White have?
55 GeneticsHair color is different from widows peak, no color is truly dominant.In Fairy tales…Brown and blond are two, true traitsHomozygous conditions produce either brown or blond hairHeterozygous conditions produce red hair
56 GeneticsFor Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charmin must be homozygous recessive, “bb”.BBbBbBbbBbBb
57 GeneticsAll the offspring from Prince Charming and Snow White will therefore be heterozygous, “Bb”, and since hair color is codominant….. all their children will have red hair.+