CHARACTERISTICS OF LIFE All Living Things reproduce All

CHARACTERISTICS OF LIFE All Living Things reproduce!!! All Living Things Have DNA!!!

WHY ARE WE ALL DIFFERENT? We all inherited different genes from our parents which determines our traits. Heredity – Passing on of genes which determine your traits from parents to offspring. 23 chromosomes from each parent.

Genes – Pieces of DNA that carry hereditary instructions and are passed from parents. Traits – A distinguishing characteristic that is passed from parents to offspring. Genetics – Study of heredity (passing on of genes)

Johann Gregor Mendel was born July 22, 1822. Mendel became a friar at the Augustinian monastery in Brno, Czechoslovakia. From 1868 until his death, Mendel was the abbot of the monastery. Mendel was experimenting with flowers in the monastery's gardens. He wondered how traits were passed from parent to offspring. He studied the relations between parents and offspring with mathematical symbols. His favorite plants to experiment with were peas. FATHER Of genetics

MENDEL’S EXPERIMENT PART 1 He bred a tall pea plant with a pure short pea plant. But ALL the offspring were TALL. How could that be? Maybe a mistake was made? PART 2 He crossed 2 of the offspring from the above cross. Results – 75% Tall 25% Short Now wait a minute!! He crossed two tall and go a short? What’s going on? ? ?

GENETIC RULES Every organism has TWO forms of a gene for each trait. One from each parent. Each form is called an ALLELE. You can receive a dominant or recessive gene From your parent.

GREGOR MENDEL He realized in the first cross, one trait appeared and the other seemed to be masked. * The trait that masks or is stronger than the other trait is called the dominant trait. * The trait that is covered up is called the recessive trait. For these reasons, Mendel is called the Father of Genetics.

GENETICS RULES and SYMBOLS Scientists use symbols to represent different forms of a gene. Capital Letters – Represents dominant trait. Dominant traits are the stronger traits. Lower Case Letters – Represents recessive trait. Recessive traits are the weaker traits that are often masked by dominant traits. Examples-BB – brown eyes Bb – brown eyes bb - blue

Example Dominant Traits Brown Eyes- B Widow’s Peak- W Unattached Earlobes- E Freckles- F Example Recessive Traits Blue eyes- b Straight hairline- w Attached earlobes- e No Freckles- f

Homozygous vs. Heterzygous If the inherited genes (alleles) are the same, then they are called HOMOZYGOUS or purebred. Letters are the same size. Examples – aa , AA , LL , ll , TT , tt If the inherited genes are different, then they are called HETEROZYGOUS or hybrid. Letters are different sizes. Examples – Aa , Ll , Tt, Bb

Genotype vs. Phenotype The genotype is the letter combination or gene combinations Example – Tt, Aa, bb, or Ll The phenotype is the actual appearance of the organism. Example – tall, brown hair, blue eyes, long toes

GENETIC PROBABILITY Mendal crossed yellow and green pea plants and discovered that 1 out of 4 were green. He was using probability. Probability – The possibility or likelihood that a particular event will occur. Used to predict the results of genetics crosses.

PUNNETT SQUARES A Punnett square is a special chart used to show the possible gene combinations in a cross between 2 organisms. (also called Developed by monohybrid crosses) an English geneticist by the name of Reginald Punnett.

PARTS OF A PUNNETT SQUARE Male Genes Female Genes T= tongue roll t= cannot roll tongue Offspring Combinations

How does a Punnett Square Work? • Draw a square and divide it into 4 sections. • Write the gene pairs across the top of the box, then the other down the side. • In each box, place the correct gene to see the possible combinations. Each square represents a 25% possibility of getting that trait.

Tt Tt Cross between homozygous dominant curly tail (TT) and a homozygous recessive straight tail (tt).

Tt Tt What are the percentages of the offspring? What are the genotypes? What are the phenotypes?

TT Tt Tt tt Cross between two heterozygous curly tailed parents (Tt). What are the percentages of offspring? What are the genotypes? What are the phenotypes?

Mathematical Computations In a Punnett Square where both parents are hybrids the percents are listed below: 25% purebred (homozygous) curly – TT 50% hybrid (heterozygous) curly - Tt 25% purebred (homozygous) straight - tt % of same genotype as parents - 50 % % of same phenotype as parents - 75%

Dihybrid Crosses A dihybrid cross is a cross of two different traits Mom T t T- height S-shape T-tall S-square Dad S S s s List of gamete genotypes: Mom. Dad- t-short s-round T t

Dihybrid crosses- formation of zygote Mom- ST, St, s. T, st Dad- ST, St, s. T, st When parent gametes (egg/sperm) join to form a zygote, the possible offspring gene combinations are as follows: Formation of zygote ST (egg) St (egg) s. T (egg) st (egg) ST (sperm) St (sperm) s. T (sperm) st (sperm)

Dihybrid Crosses Parent generation = gene pairs given by parents. Gametes = half of parent gene pair 1 st Generation= combination of gametes to produce offspring. 2 nd Generation= possible combination of offspring from 1 st generation cross The possible gene combinations from 1 st generation offspring

Practice G-eye size G-large g-small B- eyebrows B-separated b-attached

The squares contain the gene combinations that could occur in the cross. The genotype is the letter combination or gene combinations in the squares. Example – Tt, Aa, bb, or Ll The phenotype is the actual appearance of the organism. Example – tall, brown hair, blue eyes, long toes

INCOMPLETE DOMINANCE Sometimes, you may notice that traits can blend together. Two capital letters are used. For example: Red & White are equally dominant producing Pink flowers. Examples – roan color in horses and cows, pink color in flowers are red and white combined.

Codominance When both alleles contribute to the phenotype. For example: Chickens- black & white feathers are codominant, therefore they can appear speckled.