Heredity
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Presentation Transcript
Your Physical Appearance • Heredity is the passing of traits from parents to an offspring. • Gregor Mendel was the first scientist to successfully study inheritance • He is the “Father of Genetics”
Why Pea Plants? • Mendel use Garden Pea Plants for his research because: • They grow quickly • They naturally self-pollinate
Mendel’s Success • Mendel was successful with his pea plant research because: • he studied one trait at a time! (independent variable) • He had studied statistics *A trait is a distinct phenotypic characteristic that may be inherited
Pea Plant Traits • Flower Color • Flower Position • Seed Color • Seed Shape • Pod Shape • Pod Color • Plant Height
The Experiment • Mendel began by taking pure trait plants and cross-pollinating them • He did this by hand, not with bees!
The Experiment Part I (Example 1) Plant height Mendel crossed a Tall parent plant with a short parent plant: Tall x short = All Tall TT x tt = Tt parent 1 x parent 1 = First Filial (F1) Both parent plants were true-breeding: They always produced the same type of offspring.
The Experiment Part I (Example 2) Flower Color Mendel crossed a Purple parent plant with a white parent plant: Purple x white = All Purple PP x pp = Pp parent 1 x parent 1 = First Filial (F1)
The Experiment Part II • He wondered why one trait disappeared when he crossed the two pure (true-breeding) plants • He decided to allow the new F1 plants to naturally self-pollinate and here is what he found……..
Example 1- Plant Height F1 Tall plants self-pollinate and produce: 75% Tall Plants 25% short plants
Example 2 - Flower Color F1 Purple Flower color plants self-pollinate and produce: 75% Purple flowers 25% white flowers
Mendel’s Conclusion • The Principle of Dominance and Recessiveness states that one trait is more likely to occur than the other. • Dominant is a trait that is most likely to occur • Recessive is a trait that is usually hidden in the first generation, but may reappear later
Probability • The chance or possibility that a certain outcome will occur. Usually written as: • Fractions • Decimals
Genotype- the genetic make-up of an organism (TT, Tt, tt) Phenotype- the physical appearance of an organim (Tall, short, Purple, white) Dominant- more likely to occur (The tall plants or the purple flowers) Recessive- less likely to occur (The short plants or the white flowers) Let’s Learn a New Language..
Let’s Learn a New Language.. • Homozygous- when both alleles are the SAME • Homozygous Dominant: TT, PP, WW • Homozygous Recessive: tt, pp, ww • Heterozygous- when each allele is DIFFERENT • Tt, Pp, Ww
Let’s Learn a New Language.. • An Allele is an alternate form of a gene; one part of a pair • A Gene is composed of two alleles, one from each parent Allele + Allele = Gene T(mom) + t(dad) = Tt(child)
Punnett Squares • Developed by Rudolph Punnett to make genetics easier for us to understand
Genetics Example 1 In garden pea plants, tall plants are dominant (T) and short plants are recessive (t). A pea plant that is homozygous dominant for height is crossed with one that is homozygous recessive for plant height. • Draw a Punnett square to represent the problem. • What are the possible genotypes? • What are the possible phenotypes? • What is the probability of each genotype? • What is the probability of each phenotype?
Genotypes • Phenotypes • Probability of genotypes • Probability of phenotypes
Genetics Example 2 In garden pea plants, purple flower color (P) is dominant over white flower color (p). A pea plant that is homozygous recesive for flower color is crossed with one that is heterozygous for flower color. • Draw a Punnett square to represent the problem. • What are the possible genotypes? • What are the possible phenotypes? • What is the probability of each genotype? • What is the probability of each phenotype?
Genotypes • Phenotypes • Probability of genotypes • Probability of phenotypes
Genetics Examples In garden pea plants, yellow seeds (Y) are dominant and green seeds (y) are recessive. What offspring would result if two heterozygous plants were crossed? • Draw a Punnett square to represent the problem. • What are the possible genotypes? • What are the possible phenotypes? • What is the probability of each genotype? • What is the probability of each phenotype?
Genotypes • Phenotypes • Probability of genotypes • Probability of phenotypes
Incomplete Dominance • Sometimes one trait is not completely dominant over the other • The same letter allele is used • Red x White = Pink RR x R’R’ = RR’ • This results with a combined genotype • Snap dragons
Codominance • Sometimes both traits are equally dominant • Different letter alleles are used • Black x White = Checkered BB x WW = BW • This results in both traits being expressed • Checkered Chickens
Alternate forms of Genetics • Gregor Mendel studied simple genetic inheritance: • Offspring were either dominant or recessive • But not all traits are simple!!
Thomas Hunt Morgan • Studied Fruit Flies • Discovered • Gender inheritance • Other traits associated with gender
Gender • Gender is always determined by the male
Sex-linked Traits • Some traits are only located on the “X” chromosome • Since Males only have one “x” chromosome, they are more likely to show the trait than a female with two “x” chromosomes
Sex-linked Traits • Colorblindness • Hemophilia • Muscular dystrophy
