Mendelian Genetics Chapter 10 and 12

Gregor Mendel (a little history) “Father of Genetics” Conducted experiments on heredity with pea plants.

Mendel’s Work With Pea Plants Garden Peas

Mendel’s Work With Peas

Example cross: What do you think the offspring will look like?

The Results (F1 generation)

The Results (F2 generation)

Generations Notice that Mendel looked at 3 generations in his crosses. P = the original Parents (the first ones he crossed F1= the offspring of the P generation F2 = the offspring of the F1 generation

Important Vocabulary Heredity—the passing on of characteristics from parents to offspring Genetics—study of heredity Traits– inherited characteristics Gametes Fertilization Zygote

Do you recall… Answer the following: Gregor _______ is the Father of ______. Heredity is the passing of ______. Genetics is the study of ________.

More Vocabulary: Gene= section of DNA on a chromosome that controls a specific trait. Allele: alternate form of a gene Ex. tall allele vs. short allele for the “height gene”

Vocab… Dominant—the trait that is observed (masks the other allele) in a hybrid. Upper case letter Recessive—the trait that gets masked (not observed) in a hybrid Lower case letter

Is the trait dominant or recessive? This is a ______ trait.

Is the trait dominant or recessive? This is a ______ trait.

Vocab… Phenotype Vs. Genotype Genotype—The gene combination of the organism (i.e. BB, Bb or bb.) Phenotype – the way an organism looks and behaves as a result of its genotype (i.e brown)

Vocab… Homozygous vs. heterozygous Homozygous—has two of the SAME alleles for a trait Ex. Heterozygous—has two DIFFERENT alleles for a trait Carrier = a carrier is heterozygous. In a heterozygous creature, which trait will show up as the organism’s phenotype?

Genetics Vocab Assignment Vocab Word Explanation (your own words) Example/Drawing Gene Allele Dominant Recessive Genotype Phenotype Homozygous Heterozygous Carrier

How to Solve Genetics problems READ and Make a Key ex. B= black fur, b= white fur Parent genotypes (Write them down) ex. BB x Bb Gametes (Figure out what the gametes would be & put them on Punnett square) Fill in Punnett square to get offspring Phenotypes/Genotypes of offspring (Write them out)– Best if written as a reduced fraction! Example…

B BB Bb Monohybrid Cross Punnett Square Cross for one characteristic Example: Hair color B b B BB Bb Punnett Square C:\Documents and Settings\BBAUGHMAN\Desktop\bio powerpoints\Chapter 10 BDOL IC

Practice Problems 1. In pea plants, tall (T) is dominant to dwarf (t). Show the cross between a heterozygous tall and a dwarf plant. a. What are the expected genotypes and phenotypes and in what proportion? b. Show the cross between two heterozygous tall plants. What are the expected genotypes and phenotypes and in what proportion?

In goats, a recessive gene causes the goats to "faint" when they are startled. A farmer breeds two goats (that have never fainted) and their first offspring faints two days after its birth. What must the parent's genotypes have been? Show the cross to prove it. http://www.youtube.com/watch?v=we9_CdNP uJg FAINTING GOATS VIDEO CLIP

Dihybrid Cross Cross with two characteristics at the same time Example: Seed Color AND Seed shape 2 types of genes

DIHYBRID crosses (how to perform them) Exm. Parents = RrYy x RrYy Make a key Write out parents. Use FOIL method to determine gametes FOIL = first, outer, inner, last Write out possible gametes. Place the father’s gametes on the side and the mother’s on the top. Use a 16 square Punnett square (4x4)

Practice Problems In guinea pigs, short hair is dominant to long hair. Also in guinea pigs, black eyes are dominant to red eyes. A male guinea pig that is heterozygous for both traits is crossed with a female that is long haired and red eyed. a. What are the expected phenotypes of their offspring and in what proportion? b. If both parents are heterozygous for both traits, what are the expected phenotypes of their offspring and in what proportion?

Mendel’s Laws Law of Segregation When gametes are made, allele pairs segregate (separate). Then alleles randomly recombine at fertilization (with the alleles of the other parent).

Law of Independent Assortment Genes for different traits (ex. Height and seed color) are inherited independently of each other. (i.e. how tall you are will NOT affect what color your seeds are)

Genetics Problems Review On a separate piece of paper, make up three genetics problems as follows: 1. an easy monohybrid problem 2. a difficult monohybrid problem 3. a dihybrid cross You can make up any traits you like. Feel free to be creative. ex. Unibrows are dominant in snorkeloos. If a homozygous dominant snorkeloo marries a homozygous recessive snorkeloo, what are the expected genotype and phenotype ratios for their babies?

Other Inheritance Patterns Incomplete Dominance Codominance Multiple Alleles Polygenic Sex-Linked (X linked)

Pink Carnation Incomplete dominance Hybrid is a blend of traits Example: RR=red RR’ =pink R’R’=white Pink Carnation

Practice problem A cross between red snapdragons and white snapdragons produces all pink offspring. Show the cross of the F1 generation (cross two pink ones.) What is the genotype ratio? What is the phenotype ratio?

Codominance Codominance—showing both alleles at the same time Ex. *Checkered chicken (Black and white at same time) B= Black W= White So BB= Black, WW =white, and BW = black and white checkered. Another example is Blood Type! Type AB

Codominance x BB WW BW

Practice problem Background: A black rooster and a white hen have offspring that are all checkered. What inheritance pattern is this? Cross a heterozygous chicken with a white chicken. Give genotype and phenotype ratios.

Multiple Alleles TYPES: A = IAIA, IAi B = IBIB , IBi AB = IAIB O = ii Multiple alleles: more than 2 possible alleles for a gene. Ex: human blood types 3 Alleles: IA, IB, i TYPES: A = IAIA, IAi B = IBIB , IBi AB = IAIB O = ii

Practice problem Show the cross of a man heterozygous for type B blood with a woman that has type O blood Describe genotypes and phenotypes of the offspring.

Polygenic traits Polygenic trait = a trait that is influenced by more than one gene. Ex. Eye color, skin color, hair color, height… What do all of these characteristics have in common that can help you to recognize that the trait is polygenic?

Determining Sex (gender) Look at sex chromosomes (X and Y) XX = female XY = male

Sex-Linked Gene is found on a sex chromosome (usually X) Trait more commonly seen in males. Ex. Colorblindness, hemophilia Possible genotypes Female= XRXR XRXr XrXr Male= XRY XrY “Y” is empty Fruit Flies C:\Documents and Settings\BBAUGHMAN\Desktop\bio powerpoints\Chapter 12 BDOL IC

Practice problem A female carrier of colorblindness marries a normal male who is not colorblind. Describe their potential offspring in terms of genotype an phenotype probabilities.

Pedigree Charts Male = Female= Sexual Union= Offspring= Shaded= has the trait (the phenotype)

Pedigree Chart -Cystic Fibrosis

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Mendel’s Monohybrid Crosses 1st Generation: All plants were tall 2nd Generation: Mendel allowed tall plants of first generation to self-pollinate 1000 plants produced in second generation What do you think Mendel saw in the F2 generation? 1000 plants produced 750 were tall 250 were short 3:1 ratio The Short Trait Reappeared!!!

Mendelian Genetics WHAT DOES THIS MEAN????? Mendel did several similar crosses looking at various traits of the pea plant Each trait had similar results One pair of the trait disappeared in the F1generation The trait would reappear in the F2 generation WHAT DOES THIS MEAN?????

Rule of Unit Factors 2 factors control each traits of an organism These factors are genes located on chromosomes Different gene forms called Alleles Ex: tall allele (T), short allele (t) Plant can have allele (TT), (tt) or (Tt) Each allele is inherited from each parent; one from mom and one from dad

Rule of dominance When Mendel crossed tall plants with short plants he observed only tall plants were produced in the F1 generation. Dominant: observed trait Mendel concluded allele for tall plants is dominan to allele for short plants Dominant trait seen when allele is (TT) or (Tt) Recessive: trait that dissappeared Recessive trait only seen when allele is (tt)

Rule of dominance Dominant trait is always written with an uppercase letter Ex: tallness (T) Recessive trait is always written with a lowercase letter (t)

Law of Segregation Mendel’s Law of Segregation Recall, where there any short plants when Mendel crossed a tall plant with a short plant? All plants in the F1 generation were Tall When F1 tall plants were bred the shortness trait reappeared Mendel concluded each tall plant in the F1 generation carried one dominant allele for tallness and one unexpressed recessive allele for shortness

Law of Segregation Law of segregation: because each plant has two different alleles, it can produce two different types of gametes. During fertilization, male and female gametes randomly pair so there can be a combination of four different alleles (T1 T2) (T1 t2) (t1 T2) (t1 t2)

Law of Segregation

Phenotypes and Genotypes Two organisms can look alike but have different allele combinations Ex: tall plants can have allele combination (TT) two dominant alleles or (Tt): one dominant and one recessive allele. Short plants have allele combination (tt) two recessive alleles. TT Tt

Phenotypes and Genotypes Phenotype: the way an organism looks and behaves The outward physical appearance of an organism Ex: brown hair, green eyes, tall, short, etc. Genotype: The allele combination an organism contains Ex: (BB) (Bb) (bb)

Phenotypes and Genotypes You cannot always see the organism’s genotype when you know the phenotype A dominant trait can have a (Tt) or (tt) genotype but still display the dominant trait Homozygous: when the two alleles for the same trait are the same. (TT) or (tt) TT – homozygous dominant tt – homozygous recessive Heterozygous: when two of its alleles differ for the same trait Tt - heterozygous

Next Week….. Mendel’s Dihybrid Crosses Punnett squares Mendel’s law of independent assortment