Heredity

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: 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

Let’s Learn a New Language.. 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.. 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

More Genetics

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

Colorblindness Charts

Other Types of Inheritance Name: Description: Examples: Multiple Allele Traits Traits can be determined by 3 or more alleles Fur Color in Rabbits, Blood Type in Humans Polygenetic Traits Traits are determined by more than one GENE Human height, Human eye color **Most Traits that can have a “range”