Genetics & Heredity
HEREDITY def: the passing of traits from parent to offspring.
GENETICS def: The study of heredity.
*The Father of Genetics* (1822-1884) Occupation: Monk Subjects Studied: Botany (*study of plants) & Math Contributions: a.) formed basics of heredity b.) worked w/common pea plant Gregor Mendel
Mendel chose to work with the pea plant for two main reasons: 1.) They normally self-pollinate, which allows him to create pure strains. 2.) He could cross-pollinate the pea plants, which allowed him to test the crossing of various plants. *Mendel s work was rejected during his lifetime.*
Characteristics of Pea Plant Studied by Mendel
Laws of Genetics Mendel came up with 3 laws that governed genetics of organisms: 1. 2. 3. 4. Law of Dominance and Recessiveness Law of Segregation Law of Independent Assortment Rule of Unit Factors
Principle of Dominance & Recessiveness 1. Some genes are dominant. 2. They express themselves over recessive genes. Dominant genes are indicated by capital letters. Ex: D Some genes are recessive. They are masked (or covered up) by the dominant gene. Recessive genes are indicated by lower case letters. Ex: d
Principle of Dominance & Recessiveness, cont. Phenotype def: external appearance; physical, outward expression of genetic makeup Genotype def: the combination of genes; genetic makeup of organisms (GG, Gg, gg)
Principle of Dominance & Recessiveness, cont. Types of Genotypes: A. Homozygous dominant (Purebred) *(prefix HOMO - means same or alike) -Two genes that are the same and dominant Ex: TT, WW, GG B. Homozygous recessive (purebred) -Two genes that are the same and recessive Ex: tt, ww, gg C. Heterozygous (hybrid) *(prefix HETERO - means different) -Two genes that are different Ex: Tt, Ww, Gg
Law of Segregation States that 1. The two genes for a trait separate during the formation of gametes. 2. This happens during meiosis I, anaphase I. 3. The offspring receives one allele from each parent
Law of Independent Assortment States that 1. The genes are located on different locations on chromosomes. 2. Genes for different traits are inherited independently of each other.
Rule of Unit Factors Each organism has two alleles for each trait Alleles - different forms of the same gene Genes - located on chromosomes, they control how an organism develops
Main types of genetic crosses: 1. Monohybrid Cross 2. Dihybrid Cross 3. *Trihybrid Cross
Steps to solve a Punnett Square Punnett Square: def: a method of predicting the inheritance of traits by offspring. Step 1: Determine the gametes produced by each parent. Step 2: Set up and fill in the Punnett square w/each gamete. Step 3: Determine the ratios and percent probabilities.
Monohybrid Cross def: a cross between parents who differ by only one trait. Ex: two mice that differ only in fur color. One mouse has brown fur and the other has white.
Monohybrid Cross: Step 1: Determine the gametes of parents. homozygous x homozygous BB x bb Write the gametes in the Square. Step 2: Example: Fill in the genotypes of the offspring. In rabbits, black fur (B) is dominant over brown fur (b). Step 3: Determine genotypic ratio & percentages. Step 4: Determine phenotypic ratio & percentages.
Monohybrid Cross: homozygous x heterozygous BB x Bb Step 1: Determine the gametes of parents. Write the gametes in the Square. Step 2: Example: In rabbits, black fur (B) is dominant over brown fur (b). Fill in the genotypes of the offspring. Step 3: Determine genotypic ratio & percentages. Step 4: Determine phenotypic ratio & percentages.
Monohybrid Cross: heterozygous x heterozygous Bb x Bb Step 1: Determine the gametes of parents. Write the gametes in the Square. Step 2: Example: In rabbits, black fur (B) is dominant over brown fur (b). Fill in the genotypes of the offspring. Step 3: Determine genotypic ratio & percentages. Step 4: Determine phenotypic ratio & percentages.
Dihybrid Cross def: a cross between parents who differ by only two traits. Ex: two parents that differ only in hair style & freckles.
Dihybrid Cross, example T = Tall, t = short P = Purple, p = white Dihybrid Cross of TtPp X TtPp TP Tp tp tp TP TTPP TTPp TtPP TtPp Tall/Purple Tall/Purple Tall/Purple Tall/Purple Tp TTPp TTpp TtPp Ttpp Tall/Purple Tall/white Tall/Purple Tall/white tp TtPP TtPp ttpp ttpp Tall/Purple Tall/Purple short/purple short/purple tp TtPp Ttpp ttpp ttpp Tall/Purple Tall/white short/purple short/white
Dihybrid Cross Ex: 1.) Freckles is dominant over no freckles. (F, f) 2.) Widow s peak is dominant over a straight hairline. (G,g) Parents: FfGg x FfGg *Determine 4 Phenotypic Ratios
Types of Dominance *(3) Codominance Incomplete Dominance Complete Dominance
Incomplete Dominance (Mixture) F1 Pure Red (RR) x Pure White (WW) *Both alleles are blended in the hybrid genotype. *Snapdragon flower RR = Red RW = Pink *(different) WW = White F2 - Pink (RW) x Pink (RW)
Incomplete dominance EX.
Codominance *Neither phenotype is dominant over the other. *The hybrid shows both phenotypes equally Both phenotypes can be seen in roan-colored cows and horses. (*not a mixture of colors as in incomplete dominance) RR Red WW White RW Roan
Codominance EX.
Codominance: in humans Blood Type: A & B are equally strong. O is recessive. IAIO is Type A IBIO is Type B IAIB is Type AB IOIO is type O
Codominance: in humans Blood Type: phenotypic ratio 1:1:1:1 1 type A 1 type B 1 type AB 1 type O IA IB IO IO IA IB IB IO IA IO IO IO
Sex-Linked Traits Boy or Girl? The Y Chromosome Decides X chromosome Y chromosome
What are Sex Linked Traits? In 1910, Thomas Morgan discovered traits linked to sex chromosomes in fruit flies. Some genes are attached to the X and Y chromosomes EXAMPLE: In humans, color blindness and baldness are found on the X chromosomes
Can you trace a line from one "X" to the other? Someone with normal color vision will trace a orange/brown purple line and those with a slight deficiency will follow a different path.
What are Sex Linked Traits? In Men, traits expressed anytime present In Women, must have two genes to show trait Children inherit baldness from their mothers
Punnett Square: What sex will the offspring be? Answer on your own paper. 50% chance of a male or a female child.
Baldness is carried by the mother Phenotype: 25% bald males 25% bald carrier females 25% not bald males 25% non-carrier females
If Dad is bald, will you be bald? Phenotype: 0% bald males 100% bald carrier females
What if Mom is bald? Phenotype: 100% carrier females 100% bald males
Bellringer 11/9 Get out your notebook and glue your genetics notes on page 33 titled Genetics Part 1 Notes Then create a page 34 titled Punnett Practice and quietly wait for class to start