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Medelian Genetics Laws of Inheritence. Key Terminology Phenotype the appearance of the trait in the organism Genotype The genetic makeup of an organism.

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Presentation on theme: "Medelian Genetics Laws of Inheritence. Key Terminology Phenotype the appearance of the trait in the organism Genotype The genetic makeup of an organism."— Presentation transcript:

1 Medelian Genetics Laws of Inheritence

2 Key Terminology Phenotype the appearance of the trait in the organism Genotype The genetic makeup of an organism Genetics biology dealing with the principles of variation and inheritance in animals and plants. gives us greater understanding of how we can determine the likelihood of inheriting certain phenotypes.

3 Brief History of Genetics 19 th Century Greeks believed in a blending theory of inheritance.

4 History of Genetics: Darwin Charles Darwin – theorized that offspring have variations of their parents' characteristics, but he was unable to explain why (1870s).

5 Gregor Mendel ( ) o Austrian monk Used pea plants to study genetics, heredity and variation. Looked at 7 different traits that only had two variations From his meticulous work he came up with many “key terms” and, more importantly, two generalizations that later became known as Mendel’s Laws Considered the father of genetics (now aka Mendelian Genetics)

6 Why the pea plant? grows easily and quickly has seven traits that are easily identified it is easy to manipulate pollination

7 Mendel's Pea Plant Experiment Mendel started by breeding purebred plants for different traits. Purebred: Individuals that only contain one variation of a trait and therefore can only pass this one variation on to future generations. We now call these individuals homozygous, or having two alleles that are the same.

8 Mendel’s Experiments: F1 Generation Obtained plant “purebreds” (P* - parent generation) Only use this notation if parents are purebred Crossed each P generation with it’s opposite Example: Tall plant P is crossed with a short plant P This produced the F1* generation F1 – first filial generation Only use this notation if hybrid offspring of two purebreds Product of this cross is know as a hybrid since it is a cross between two different purebreds More commonly this is called a Monohybrid Cross Only one trait was selected – plant height

9 Mendel’s Pea Plant Experiment He cross-fertilized the purebred plants to see what would happen. For example: Tall plant x dwarf plant What do you think the offspring looked like?

10 Mendel's Pea Plant Experiment 100% of the offspring plants were tall! Parent (P) generation – original generation that produced offspring Filial (F1) generation –offspring from the cross (reproduction) of the P generation.

11 Mendel's Pea Plant Experiment 100% of the offspring plants were tall! Parent (P) generation – original generation that produced offspring Filial (F1) generation –offspring from the cross (reproduction) of the P generation.

12 Mendel's Pea Plant Experiment Mendel then let the F 1 cross pollinate… This time most were tall, but some were short!

13 Pea plant crosses X x

14 Why? Each plant in the F1 generation carried an allele from the P generation, a tall allele (T) and a dwarf allele (t). They are what are called hybrids. (Ex. Tt) Hybrids: Individuals that contain more than one variation of a trait and therefore can pass on more than one variation to future generations. We now call these individuals heterozygous, or having two alleles that are different from each other.

15 Terminology Review Traits are dominant or recessive. If a dominant trait is inherited, it will be expressed. The recessive trait is only expressed if both inherited alleles are recessive. What is the dominant trait for height in pea plants?

16 Terminology Review Phenotype: The appearance of traits in an organism (Ex. Tall or Short) Genotype: The specific genes an organism has (Ex. Which alleles, dominant or recessive, homozygous or heterozygous) Every individual has a phenotype and genotype for every trait The phenotype is easy to figure out but the genotype is hard to determine especially for dominant traits

17 Mendel's Laws and Principles The alleles we have came from our parents. At conception the sperm and egg unite each donating one copy of every gene. Law of Segregation : when any individual produces gametes (sex cells), the copies of a gene separate so that each gamete receives only one copy of a gene and therefore only one allele for all possible traits.

18 Mendel's Laws and Principles Law of Independent Assortment: alleles of different genes assort independently of one another during gamete formation, so different traits are inherited independently of each other (as long as they are on different chromosomes) In English, this means that if you are able to be dominant for one trait, it will have no influence on whether you will be dominant for another trait

19 Summary: Plant Height tt P Generation F 1 Generation F 2 Generation True-breeding parents Tall = dominant = T Short = recessive = t TTtt Hybrid offspring All heterozygous all Tt Monohybrid cross from F 1 generation TTTt Tall all Tall Tall short Genotypes 1 TT : 2 Tt : 1 tt Phenotypes 3 Tall : 1 short

20 Punnett Squares Probability – the likelihood of an outcome Monohybrid Cross: a mating between organisms where only one trait is being examined Punnett square - used to determine the probabilities of allele combinations when the genotypes of the parents are known

21 Punnett Square Example Brown fur ( B) is dominant to grey fur (b) What are the genotypic and phenotypic outcomes for offspring between a homozygous recessive mother and homozygous dominant father?

22 Steps to Punnett Squares 1) Determine which allele is dominant and which allele is recessive B (brown fur) = dominant, b (grey fur) = recessive 2) Determine the genotypes of the parents Homozygous recessive mother – bb Homozygous dominant father – BB BB x bb

23 Steps to Punnett Square 3) BB x bb Prepare your square, write the genotype of one parent on the top of the square, one allele over each column, the genotype of the other parent on the left, one allele for each row.

24 Steps to Punnett Square 4)Each time the parents mate, they can donate ONE of their 2 alleles for the trait. Inside the grid, combine the alleles from each parent in each square to make four possible genotypes. ** Always write the dominant letter first. Keep your letters clear so you can distinguish between upper and lower case letters **

25 Punnett Square Example 5) Re-read the question and use the results to state your answer.

26 Punnett Square Example What are the genotypes of the parents? What are the genotypes probabilities? What are the phenotype probabilities?

27 Genetics in Harry Potter What types of inherited traits are described in the Harry Potter series?

28 Inherited Physical Traits in Harry Potter "All the Weasleys have red hair, freckles, and more children than they can afford.” - Draco Malfoy (Sorcerers Stone, Ch.6) “He was almost twice as tall as a normal man and at least five times as wide.” - (Socerers Stone, Ch. 6) “Harry had a thin face, knobby knees, black hair, and bright green eyes” - (Sorcerer’s Stone, Ch.1) “A pale boy with a pointed face and white- blond hair, Draco greatly resembled his father. His mother was blonde too…” - (Goblet of Fire, Ch.8)

29 Inherited Physical Traits in Harry Potter What are some phenotypes (observable traits) described in the four excepts from the Harry Potter books? Freckles, Hair Colour, Eye Colour, Height

30 Weasley Freckles Two possible phenotypes for freckles are: Has Freckles (observable) No freckles (observable) A genotype for freckles is indicated by two alleles in the freckle gene. The possible alleles using the first letter of the trait “f” are: F (dominant) = Has Freckles f (recessive) = No freckles Question: Using F and f, what are possible genotypes of the allele pair for freckles?

31 Freckles: Genotypes and Phenotypes Question: Using F and f, what are possible genotypes of the allele pair for freckles? Genotype Phenotype (alleles inherited from parents) (physical appearance) F F has freckles F f has freckles f f no freckles One dominant allele (F) is sufficient for its trait (has freckles) to be observable, but both alleles have to be recessive (f) for the recessive trait (no freckles) to be observable.


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