Genetics Biology Genetics The study of heredity how traits are passed from parent to offspring x or or The study of heredity started with the work of Gregor Mendel and his ID: 919763
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Slide1
Introduction to Mendelian Genetics
Biology
Slide2Genetics - The study of heredity, how traits are passed from parent to offspringx
=
or
or
Slide3The study of heredity started with the work of Gregor Mendel and his pea plant gardenMendel was an Austrian Monk that lived in the mid 1800’s
Slide4Mendel’s Laws of HeredityWhy we look the way we look...
Slide5What is heredity?The passing on of characteristics (traits) from parents to offspringGenetics is the study of heredity
Slide6Gregor MendelMendel used pea plants to discover the mechanism of heredity – how traits get passed from parents to offspring.
Slide7Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.
Slide8Why Mendel used peas...They reproduce sexuallyThey have two distinct, male and female, sex cells called gametesTheir traits are easy to isolate
Slide9Mendel crossed the PlantsFertilization - the uniting of male and female gametesCross - combining gametes from parents with different traits
Slide10QuestionsWhat did Mendel cross?What are traits?What are gametes?What is fertilization?What is heredity?What is genetics?
Slide11What Did Mendel Find?He discovered different laws and rules that explain factors affecting heredity.
Slide12Phenotype & GenotypePhenotype - the way an organism looksExample - red hair or brown hairgenotype - the gene combination of an organismAA or Aa or
aa
Slide13Heterozygous & HomozygousHeterozygous - if the two alleles for a trait are different (Aa)Homozygous - if the two alleles for a trait are the same (AA or aa
)
Slide14Dihybrid vs MonohybridDihybrid Cross - crossing parents who differ in two traits (AAEE with aaee)Monohybrid Cross - crossing parents who differ in only one trait (AA with aa
)
Slide15Questions...What is the phenotype?What is the genotype?What is homozygous?What is heterozygous?What is monohybrid crossing?
Slide16Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants.X=
X
=
Tall plants
Short plants
Slide17Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. x=
Slide18Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small.
x
=
Slide19What Did Mendel Find?He discovered different laws and rules that explain factors affecting heredity.
Slide20Mendel’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.
Slide21Carrying the information are chromosomesChromosomes are made up of sections called genesGenes are made up of DNA
Slide22Rule of Unit FactorsEach organism has two alleles for each traitAlleles - different forms of the same geneGenes - located on chromosomes, they control how an organism develops
Slide23Slide24Rule of DominanceThe trait that is observed in the offspring is the dominant trait (uppercase)The trait that disappears in the offspring is the recessive trait (lowercase)
Slide25Questions...What do we call the trait that is observed? What case (upper or lower) is it written in?What about the one that disappears? What case is it written in?
Slide26Law of SegregationThe two alleles for a trait must separate when gametes are formedA parent randomly passes only one allele for each trait to each offspring
Slide27Law of Independent AssortmentThe genes for different traits are inherited independently of each other.
Slide28Questions...How many alleles are there for each trait?What is an allele?How many alleles does a parent pass on to each offspring for each trait
Slide29Segregation - Alleles separateTtTtHeterozygous parents
T
T
t
t
Gametes
Slide30Fertilizaiton
T
T
t
t
Gametes
T
t
T
T
Parent 1
Parent 2
t
t
T
t
F
2
Generation
Slide31Slide32ProbabilityThe likelihood that a particular event will occur is called_______.Probability
Slide33ProbabilityThe probability that a single coin flip will come up heads is…a. 100 percent b. 75 percentc. 50 percent d. 25 percent
Slide34ProbabilityThe probability that a single coin flip will come up heads is….a. 100 percent b. 75 percentc. 50 percent d. 25 percent
Slide35ProbabilityIs the following sentence true or false? The past outcomes of coin flips greatly affect the outcomes of future coin flips.False
Slide36ProbabilityWhy 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.
Slide37Punnett SquaresHow do geneticists use Punnett squares?Punnett squares can be used to predict and compare the genetic variations that will result from a cross.
Slide38Genetics & Punnett SquaresFirst 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
Slide39Dominant and Recessive GenesA 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 peak Widows Peak
Slide40GeneticsPunnet 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
Slide41GeneticsA Widows Peak, dominant, would be symbolized with a capital “W”, while no widows peak, recessive, would be symbolized with a lower case “w”. Father-No Widows Peak ‘w’ Mother-Widows Peak ‘W’
Slide42GeneticsAll organisms have two copies of each gene, one contributed by the father, the other contributed by the mother. Homozygous - Two copies of the same gene Heterozygous - Two different genes
Slide43GeneticsFor the widows peak: WW - has a widows peak Homozygous dominant Ww - has a widows peak Heterozygous ww - no widows peak Homozygous recessive
Slide44Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww” Definitely Homozygous recessive ww Either Heterozygous
Ww
or Homozygous dominant
WW
Slide45GeneticsWe can use a “Punnet Square” to determine what pairs of genes Lilly has
Ww
ww
Ww
ww
w
w
W
w
Assume Lilly is heterozygous
Ww
Assume Herman is homoozygous recessive
ww
A
Punnet
Square begins with a box 2 x 2
One gene is called an “allele”
One parents pair is split into alleles on top, the other along the side
Each allele is crossed with the other allele to predict the traits of the offspring
Slide46GeneticsNotice 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 peak
Ww
ww
Ww
ww
w
w
W
w
Slide47GeneticsAnother possibility is that Lilly might be “WW”, homozygous dominant.
Ww
Ww
w
w
W
W
Assume Lilly is homozygous dominant
WW
Assume Herman is homoozygous
ww
Ww
Ww
Notice that all the offspring are heterozygous and will have a widows peak
Slide48GeneticsSo which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)?
Ww
Ww
w
w
W
W
Ww
Ww
Ww
ww
Ww
ww
w
w
W
w
Slide49Ww
Ww
w
w
W
W
Ww
Ww
Ww
ww
Ww
ww
w
w
W
w
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 peak
Slide50Recall that Herman and Lilly had another offspring, Marylin. She had no widows peak, therefore, Lilly must be heterozygous.
Slide51Genetics & Punnett SquaresNow 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
Slide52Genetics & Punnett SquaresCodominant - 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
a
n
d
w
h
it
e
flower
Slide53GeneticsHair color can be an examplePrince Charming is blondSnow White has
black
hair
Slide54GeneticsWhat color hair will the offspring of Prince Charming and Snow White have?
Slide55GeneticsHair 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
Slide56GeneticsFor Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charmin must be homozygous recessive, “bb”.
Bb
Bb
b
b
B
B
Bb
Bb
Slide57GeneticsAll 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.+
Slide58That’s all for now!