Mendelian Genetics

WHO’S THE PARENT? AB

GENETICS

Gregor Mendel- The father of Genetics Lived from An Austrian Monk and Biologist Taught High School Worked with pea plants in the monastery garden.

5 Gregor Mendel’s experimental garden in the Czech Republic copyright cmassengale

Gregor Mendel Pea Plant Traits  Called the “Father of Genetics”  Mendel tested at least 28,000 pea plants  Mendel looked at 8 traits of pea plants  He found that the plants' offspring had traits of the parents

GREGOR MENDEL “Crossed”=“Mated” pea plants to look at different traits: Purple or white flowers Tall or short plants Wrinkled or round peas Yellow or green peas

8 Eight Pea Plant Traits TRAIT:LETTER WE USE: Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green ( y ) Pod Shape --- Smooth (S) or wrinkled ( s) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white ( p ) copyright cmassengale

9  Mendel stated that physical traits are inherited as “particles”  Mendel did not know that the “particles” were actually DNA on chromosomes What Mendel thought… copyright cmassengale

IMPORTANT VOCABULARY! Genetics—the study of heredity; studying the transfer of traits from one generation to the next Trait—a physical characteristic; examples: eye color, hair color, pea shape, tail length, etc. Gene—a section of DNA on a chromosome that contains the information which determines a trait Heredity— passing of traits from parent to offspring

Alleles— different forms of the same gene Example: the gene for eye color might have alleles for brown eyes and blue eyes (B=Brown, b=blue) Dominant allele—an allele that will always be seen if it comes from one parent. Written as a capital letter “B” Recessive allele—an allele that will be hidden by a dominant allele; recessive alleles are only seen if the dominant allele is missing. Written as a lower case letter “b” IMPORTANT VOCABULARY!

Genotype (gene type) — a list of the alleles that an organism has for a particular trait(s) Ex: AA, Aa, aa TT, Tt, tt Phenotype (physical type) — the physical description of the trait(s) an organism has Ex: tall, short, brown, wrinkled, smooth, red IMPORTANT VOCABULARY!

GENOTYPE PHENOTYPE Phenotype is what is seen “Phen is seen” BB brown eyes Bb brown eyes bb blue eyes

Heterozygous (hetero= different)- 2 different alleles for the same trait. ◦ Ex: Tt, Bb, Aa, Rr, Mm ◦ Also known as a hybrid. Homozygous (homo=same)- 2 identical alleles for the same trait. ◦ Ex: tt, bb, AA, RR, mm ◦ Also known as purebred IMPORTANT VOCABULARY!

15 Genotype & Phenotype in Flowers 2 Possible alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a trait. Possible combinations are: GenotypesPhenotypes copyright cmassengale RRRrRr rr RED YELLOW

Monohybrid Cross – cross involving a single trait e.g. flower color Dihybrid Cross – cross involving two traits e.g. flower color and plant height Types of Genetic Crosses

Monohybrid Cross: Punnett Square

Punnett Square Steps: 1. READ and UNDERLINE each problem 2. Make a KEY!!! 3. Make your cross mom X dad 4. Fill in your Punnett square 5. Determine probability

Lets try this together… 1) Brown eyes are dominant to blue eyes. What are the chances of getting a blue-eyed child if we “cross” (mate) 2 heterozygous brown-eyed parents? 2) Key: 3) ______X______ 4) 5 ) Genotypes Genotypic Ratio % Genotypic Ratio Phenotypes Phenotypic Ratio % Phenotypic Ratio

And Again… Grey fur is dominant to white fur in mice. Cross a white mom with a heterozygous grey dad. What are the possible colors of offspring? ______X______ 5) Genotypes Genotypic Ratio % Gen Ratio Phenotypes Phenotypic Ratio % Phen Ratio

One More Time… Purple flowers are dominant to white flowers. What color offspring would we get if we crossed a homozygous purple flower with a white flower? 5) Genotypes Genotypic Ratio Phenotypes Phenotypic Ratio

22 Generation “Gap” Parental (P 1 ) Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) ◦ From breeding individuals from the P 1 generation F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) ◦ From breeding individuals from the F 1 generation copyright cmassengale

23 Following the Generations Cross 2 Pure Plants Results in all Hybrids Cross 2 Hybrids get 3 Tall & 1 Short copyright cmassengale TT x tt Tt Tt TT, Tt, tt

24 Mendel’s Laws copyright cmassengale Law of Dominance Law of Segregation Law of Independent Assortment

25 Law of Dominance In a cross of parents that are pure for opposite traits (RR and rr), only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait (Rr). RR (round seeds) x rr (wrinkled) yields all Rr copyright cmassengale (Round seeds)

26 Law of Dominance copyright cmassengale

27 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait then come back together at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale

28 Law of Segregation copyright cmassengale

29 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses. copyright cmassengale

30 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R: round r: wrinkled Y: yellow y: green RrYy x RrYy RY Ry rY ry All possible gamete combinations copyright cmassengale

31 Dihybrid Cross RYRyrYry RY Ry rY ry copyright cmassengale RrYy x RrYy

32 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy RYRyrYry RY Ry rY ry Phenotypic Ratio is 9:3:3:1 Round/Yellow: Round/green: wrinkled/Yellow: wrinkled/green: RrYy x RrYy

33 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale

34 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCETT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale

Warm-up Warm-up On your index card, write the letter you chose and its sentence. “A lily has one allele for spotted pink petals and one allele for solid pink petals. The resulting flower has spotted pink petals. Which statement must be true?” A) The allele for solid pink petals is recessive B) The allele for spotted pink petals is recessive C) The alleles for spotted and solid pink petals are both recessive D) The alleles for spotted and solid pink petals are both dominant.

36 Incomplete Dominance and Co-dominance copyright cmassengale Non-Mendelian Genetics

Incomplete Dominance When 2 dominant genes blend together to form a new trait. EX: Red flower + White flower= Pink flower

New Rules… Incomplete Dominance Recognize: ◦ 3 rd phenotype in the mix. ◦ the offspring looks different than the parents. Both traits are dominant so we use the first letter from each trait, all capital letters. Example: Red flower =R White flower=W RR= Red WW=White RW or WR= Pink R R WW

Let’s try this… 1. Curly hair and Straight hair show incomplete dominance. When they are mixed, we get wavy hair. What hair types could we get if we mixed a wavy haired mother with a curly haired father? 2. Key: 3. ________X________ 4.

And again… 1. Black chickens and white chickens show incomplete dominance. When mixed they make grey chickens. Cross 2 grey chickens. 2. Key:3. _______X_______ 4.

Co-Dominance “Co” = together When both traits are dominant and they both are present together. Written the same way as incomplete dominance! ◦ Ex: a black chicken and a white chicken make a checkered chicken.

Give this a try… 1. Roan horses show a co-dominant trait. When you cross a white horse and a red horse, you get a roan horse. What are the chances of getting a roan horse if we cross a red horse and a roan horse? 2. Key:3. _______X_______ 4.

Sex Linked Traits

Sex-Linked Traits Traits that are carried on the sex (X) chromosome. ◦ Examples:  Colorblindness  Baldness  Ear hair  Muscular dystrophy

New Rules… Example: Colorblindness (allele = a little r) XX= normal X r X= carrier X r X r = colorblind XY= normal X r Y= colorblind

Mostly males will be affected. ***If mom expresses the sex-linked trait, all of her sons will also express the trait.**** Recognizing sex-linked traits

49 Sex-linked Traits Sex Chromosomes XX chromosome - femaleXY chromosome - male fruit fly eye color Example: Eye color in fruit flies (either red or white eyes) copyright cmassengale

50 Sex-linked Trait Practice Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female XRXR XrXr XrXr Y copyright cmassengale

51 Sex-linked Trait Solution: X R X r X r Y X R X r X r Y 50% red eyed female 50% white eyed male XRXR XrXr XrXr Y copyright cmassengale

52 Female Carriers copyright cmassengale

Let’s try this together… What are the chances of having a colorblind child if we cross a carrier mother with a normal father?

Try this… Colorblindness is a recessive sex-linked trait. What are the chances of getting a colorblind child if mom is a carrier and dad is colorblind?

And this one… Baldness (b) is a recessive sex-linked trait carried on the X chromosome. What are the chances of getting a bald child if we cross a normal mom and a bald dad?

Try this one on your own… Ear hair is a recessive sex-linked trait carried on the X chromosome. What are the chances of getting a carrier if we cross a man with ear hair and a normal woman?

Multiple Alleles and Blood Types

O ii A I A I A or I A i B I B I B or I B i AB I A I B Multiple Alleles More than two different alleles can exist for a particular trait, but only two can be present at any given time (because one allele from each parent). ◦ Ex. Blood Types – alleles are i, I A, and I B  This is how you can have A, B, AB, or O type blood. Phenotype Genotypes

Blood Type Cross I A I B I B i I A I B I B I B I A i I B i

AO B O ABBO AOOO Offspring Phenotypes: ¼ Type A ¼ Type B ¼ Type AB ¼ Type O Parents: AO x BO