heredity, genes & dna · * heredity * a gene * traits * there is typically two or more copies...
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Genetic Lesson.notebook
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February 19, 2016
HEREDITY, GENES & DNA
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Genetics
* Genetics
* Heredity
* A gene
* Traits
* There is typically two or more copies of a trait. These copies are called .
Try Human Wheel using Handout Inherited Characteristics (40)
examines the inheritance of biological traits.
is the passing of traits from parents to offspring.
is a set of instructions for a specific trait.
are controlled by GENES located on the chromosomes
alleles
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Truebreeding plants are selfpollinated and produce offspring exactly like the parent.
Crosspollination produces a combination or variety of traits from the parents.
MENDEL & HEREDITY
Gregor Mendel (Austrian) studied pea plants to see how traits pass from parent to offspring.
Pea plants were ideal for genetic experiments because:
Mendel compared the offspring of truebreeding and crosspollinated plants.
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Mendel’s Observations
Cross two true breeding white flowers.
True Breeders: individuals that only produce one characteristic.
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Mendel’s Observations
Cross two true breeding purple flowers.
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Mendel concluded that genes control the traits of the plant.
Discovered that, for the 7 pea characteristics he examined, one trait is always dominant over another
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Mendel's Experiment (Principle of Dominance)Drag one flower over the other to see the offspring produced. Then pull tabs.
.
P Generation: The Parental (first) generation.
F1 Generation: The offspring of the P gen.
F2 Generation: The offspring of the F1 gen.
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A dominant trait is a trait that appears in the offspring.
A recessive trait is a trait that does not appear in the offspring.
DOMINANT VS RECESSIVE TRAITS
Mendel's Ratios compare the number of dominant traits with the number of recessive traits.
Probability is the mathematical chance that an event or trait will occur.
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Tap the flower and observe. Tap Next and repeat through each set. Then pull tab.
“Autotroph”
Mendel’s Conclusion
Gene: The set of instructions that control a characteristic of an organism (e.g. flower color).
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For every trait, an organism has 2 alleles (one from mom and one from dad)
PP = purple plantsPp = purple plantspp = white plants
Mendel's Law of Dominance one allele will be dominant over another allele
Mendel's Conclusion
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A gene is a set of instructions for a specific trait. Offspring inherit 2 sets of genes, 1 from each parent. These combinations of 2 different forms of the same gene are called alleles.
A genotype is the combination of inheritated alleles. The 2 alleles the org. has.
A phenotype is the appearance of a genotype. The observable traits.
GENES, ALLELES & PUNNETT SQUARES
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Homozygous alleles have either both dominant or both recessive genes.
HOMOZYGOUS ALLELES
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Heterozygous alleles have 1 dominate gene and 1 recessive gene.
HETEROZYGOUS ALLELES
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Additional Terminology
Phenotype Genotype Genotype Description
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Write the alleles and fill in the Punnett squares for ...
One parent has homozygous dominant alleles, one parent has heterozygous alleles.
Both parents have heterozygous alleles.
C can curl tongue, c cannot curl.
Punnett Squares use parent alleles to construct a diagram showing all possible phenotypes for a particular trait.
C C
C
c
CC
C
C
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Problem
Consider a cross between a pea plant that is heterozygous for round seeds and a pea plant that has wrinkled seed. The allele for round seeds is dominant (R) over that for wrinkled seeds (r). Determine the genotypes of the offspring and indicate both the genotypic and phenotypic ratios.Let statements: Let R represent the dominant allele for round seeds.
Let r represent the recessive allele for wrinkled seeds.P generation: Rr X rr
Punnett Square:
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Activity
1) Monohybrid Problems 3C / Dihybrid Problem 3U
2) Breeding Pigs
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Taking it one step further....
Often in genetics the question comes up whether the inheritance of one trait would affect the inheritance of another trait?
For example if flower colour is governed by flower height?
In order to answer such a question we introduce
Dihybrid Crosses is a cross between two parents that breed true for different
versions of two traits
Lets revisit the example above....Flower colour is governed by gene PFlower height is governed by gene T
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Let P represent the dominant allele for pink colourLet p represent the recessive allele for white colour
Let T represent the dominant allele for tall heightLet t represent the recessive allele for short height
If we crossed a homozygous pink & tall flower with a homozygous white & short flower our punnet square would look like this.
PPTT X ppttAlleles assort independentlyPTPTPTPT
ptptptpt
All F1 generation have the same genotype & phenotype PpTt (Pink & tall).
However, we are still not sure whether the alleles for colour and height were inherited together or if they segregated independently.Further crossing is required. We need F2
PT PT PT PT
pt
pt
pt
pt
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PpTt X PpTt During Meiosis Alleles assort independentlyPTPtpTpt
PTPtpTpt
PT Pt pT pt
PT
Pt
pT
pt
P - pink p - whiteT - tall t - short
Conclusion
Genes that segregate independently in meiosis do not influence each others inheritancePractice Problems #1~3 pg. 136
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