FUNDAMENTALS OF GENETICS Modern Biology Chapter 9 Pages 164 - 182
Fundamentals of Genetics Objectives: • Describe how Mendel’s results can be explained by the scientific knowledge of genes and chromosomes. • Differentiate between a monohybrid cross and a dihybrid cross. • Predict & perform results of monohybrid and dihybrid crosses
Do Now • What is the genetic code? • What molecule carries the genetic code? • What is genetics?
Fundamentals of Genetics All of your characteristics or traits are unique to you. Parents may pass many of their own traits to their children, or offspring. For example, the color of your hair, the size of your feet and the shape of your nose are some of your traits.
Fundamentals of Genetics The passing of these traits from parents to offspring is called heredity. The study of heredity is called genetics. Biologists who study heredity are called Geneticists.
Fundamentals of Genetics • Look at the photographs to the right. • What traits have these babies inherited from their parent?
rpee Seeds and Plants Home> Vegetables > Peas > Pea, Easy Peasy Gregor MendelThe Father of Genetics • Genetics was founded with the works of an Austrian Monk, scientists and mathematician Gregor Johann Mendel. • He experimented with garden pea plants.
Gregor Mendel • His task of tending the garden gave him time to observe the passing of traits from parent pea plants to their offspring. • He became interested in why certain patterns of traits showed up in living things.
Mendel began his experiments by collecting seeds from his pea plants, carefully recording the traits of each plant. • Seeds from tall plants usually produced tall plants but sometimes produced short plants. • Seeds from short plants only produced short plants. • …but, “WHY?”
Mendel’s Experiments He studied 7 different characteristics in his pea plants, each with 2 contrasting traits. • CHARACTERISTIC-a distinguishing quality that an organism exhibits. • Ex: height, hair color, eye color, skin color. • TRAIT- specific hereditary options available for each characteristic. • Ex: tall height/short height, smooth/ blonde hair, brown/blue eyes, Dark/light skin.
Mendel’s Methods • He decided to grow plants that were purebred - having a trait that will always be passed to the next generation • The term strain denotes all plants that are pure for a trait.
Mendel Controlled Pollination • He produced 14 strains (one for each of the 14 traits he observed) by allowing the plants to self-pollinate for several generations • This became his Parent generation or his “P1 Generation”
Mendel Controlled Pollination • Pollination-transfer of pollen from anther (male flower part) to stigma (female flower part) • Self–Pollination– occurs on same plant • Cross Pollination– occurs between different plants
Mendel’s Methods • Then, Mendel cross pollinated plants that had contrasting traits to see what the offspring would look like. (P1 X P1- i.e. pure tall x pure short) • Would the offspring (F1 Generation – offspring of P1) be tall, short, or medium ?
Mendel’s Results • In his first crosses, Mendel found that only one of the two traits appeared in the offspring plants – (F1 generation). • For example, when he crossbred tall pea plants with short pea plants, the offspring (F1) were always tall.
After his first crosses, Mendel took those offspring plants (F1) and crossed them. • In these second crosses, both traits showed up again in the F2 generation. (F2 GENERATION-offspring of crosses between the F1 generation). • He observed that ¾ of the plants had the same trait as the F1 generation.
The same results happened in every experiment. One trait, like being tall, was always there in the first generation (F1). • The other trait, like being short, seemed to go away; only to reappear again in the second generation (F2). This happened with every set of traits that Mendel studied.
Mendel hypothesized that something in the pea plants was controlling the characteristics that came through • He called these controls “factors” (We now know that these factors are really traits controlled by Genes)
Because each characteristic had two forms, he said there must be a pair of “factors” controlling each trait. • Each pair consists of alternate forms (we now call alleles) of the same trait; one from mother and one from father.
MENDEL’S 3 CONCLUSIONS: Based on his findings, Mendel formulated three laws or principles of heredity: 1. Principle of Dominant and Recessiveness 2. Principle of Segregation 3. Principle of Independent Assortment
Principle of Dominant & Recessiveness Through crossing thousands of pea plants, he was able to conclude that that both of these factors (alleles) together controlled the expression of a trait. Dominant traits were controlled by dominant alleles and recessive traits were controlled by recessive alleles.
Principle of Dominant & Recessiveness DOMINANT-can mask or dominate the other ‘factor’ and is displayed most often. RECESSIVE-the ‘factor’ that can be covered up; is displayed less often. • Ex: the ‘factor’ (allele) for tall is dominant over the ‘factor’ (allele) for short, so the short allele would be the recessive allele.
Principle of Dominant & Recessiveness • Letters are used to represent the alleles that carry the trait found on genes • If the gene that controls the trait is dominant, the letter is written in uppercase. If the gene is recessive, the letter is written in lowercase. • i.e. T- represents a dominant trait for tallness; t – represents a recessive trait for lack of tallness, or shortness
T – dominant allele for tallness • t – recessive allele for lack of tallness or shortness. • W – dominant allele for round or smooth seeds • w – recessive allele for wrinkled seeds • P – dominant for flower color (purple) • p – recessive allele for white flower
Vocabulary Review GENE- a segment of DNA that codes for a specific characteristic. • Ex: height ALLELE-the different forms of a gene (Mendel’s “factor”) Ex: allele for brown eyes is B/ allele for blue eyes is b SO…if BB is a brown eyed person and bb is a blue eyed person, what color eyes does someone with Bb have?
Principle of Segregation • Each parent has two factors (copies of each trait) and they segregate, or separate into different sex cells (gametes) • Each gamete gets only 1 factor (allele) of each trait
Principle of Independent Assortment • Mendel also crossed plants that differed in 2 characteristics, such as flower height and flower color. • The data from these crosses showed that dominant traits do not always appear together ttP?
Principle of Independent Assortment • The alleles for different genes on different chromosomes are not connected. • The alleles for different traits are distributed into gametes independently (randomly) from each other.
Do Now • Who is the father of genetics? • What type of organism did he work with? • What are dominant and recessive traits?
Vocabulary Review • Chromosomes – made of DNA • Gene – segment of DNA that controls a specific hereditary trait. • Because chromosomes occur in pairs, genes occur in pairs • Allele - (Mendel’s “factor”) – contrasting form of a gene • Dominant allele – capital letter • Recessive allele – lowercase letter
AFTER MENDEL • Today, Geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses. • Why would geneticists want to predict the probable genetic make up and appearance of offspring resulting from specified crosses?
GENOTYPE & PHENOTYPE • GENOTYPE-the genetic makeup of an organism (the combination of alleles an organism inherits). • Use 2 letters together to represent genotype. • PHENOTYPE-the trait displayed based on the genotype. Ex: BB – Brown eyes • bb – Blue eyes • Bb – Brown eyes
Blue alleles b b Phenotype Genotype
GENOTYPE & PHENOTYPE • Organisms with different genotypes may have the same phenotype. • For example, a brown-eyed organism (BB) and a brown eyed organism (Bb) have different genotypes. • However, they have the same phenotype, which is brown eyes
Brown Alleles Brown Alleles B b B B One pair of chromosomes for eye color One pair of chromosomes for eye color
GENOTYPE & PHENOTYPE • HOMOZYGOUS- organism has 2 of the same alleles for a trait. • HomozygousDominant-has 2 dominant alleles; dominant trait is displayed • Ex: BB = Brown-eyed organism • Homozygous Recessive-has2 recessive alleles; recessive trait is displayed • Ex: bb = blue-eyed • HETEROZYGOUS-organism has 1 dominant and 1 recessive allele; the dominant trait is displayed. • Ex: Bb = brown eyes
Blue alleles Brown Allele Blue Allele b b b B Homozygous – alleles are the same Heterozygous – alleles are different
Do Now • What are Mendel’s Laws of Inheritance? • What is an allele? What is homozygous vs. heterozygous? • What is genotype vs. phenotype?
Probability • In order to understand genetics you need to have some basic concepts concerning probability. • Probability – the likelihood that a specific event will occur • Can be expressed as a decimal, percentage, ratio or fraction. P= number of times an event is expected to happen number of opportunities for an event to happen