Genetics Unit Chapters: 11 and 14

Father of Genetics Studied the genetics of Pea Plants He found 7 distinct traits (characteristics) in pea plants.

Mendel’s Work He Cross-Pollinated two different pea plants and produced a “HYBRID.” Hybrids are a mix of genes from 2 parents. What height do you think the offspring would be?

P Generation F 1 Generation TallShortTall Section 11-1 Principles of Dominance Cross-pollination of a Pure-tall with a pure-short plant P = Parental generation F 1 = first generation Mendel next crossed two F 1 offspring…what do you think the F 2 offspring looked like?

F 1 GenerationF 2 Generation Tall Short Section 11-1 Principles of Dominance Crossing Two F 1 Offspring… These crosses lead to his first principle of genetics…

Mendel’s Conclusions Principle of Dominance – some genes are dominant and others are recessive. Genes are the factors that determine traits. Genes have different forms called “alleles.” Ex: T – tall t - short Principle of Segregation – alleles separate during meiosis (gamete formation). Ex: If parent has alleles Tt, only one allele makes it into an egg or sperm.

How Can Genes Be Predicted? Probability: the likelihood that an event will occur. What is the probability for a coin to land on heads? Chance (segregation) of alleles is random, just like a coin flip… What is the probability for a child to be a boy? Males have 2 sex chromosomes XY. Meiosis separates the pair so only ONE of the chromosomes makes it into a gamete. So, each gamete (sperm or egg) has only one allele for a trait. x Y

Section 11-2 How to diagram using Punnett Squares Alleles segregate during meiosis into separate gametes

Section 11-2 There is a 25% chance or ¼ chance of getting a short plant from these parents. What is the chance that a tall offspring will be produced?

Crucial Genetic Vocabulary!!! You must memorize to understand genetic problems Homozygous – identical alleles for a trait or pure. Ex: tt, TT Heterozygous – two different alleles or hybrid. Ex: Tt Genotype – Allele forms for a trait. Ex: TT, Tt, or tt Phenotype – physical characteristics of the allele combination. (TT and Tt are TALL, tt is SHORT)

Let’s Practice… Purple flowers are dominant over white. 1. What is the allele for purple? 2. What is the allele for white? 3. What is the genotype for a purple flower? 4. What is the genotype for a white flower? 5. What is the phenotype for Pp? pp? 6. What is the genotype for a heterozygous purple flower? 7. What is the genotype for a homozygous white flower?

Smooth seed coat is dominant over rough seed coat. 1. Genotype for a rough seed coat? 2. Phenotype for a SS genotype? 3. Genotype for a homozygous smooth? 4. Genotype for a heterozygous smooth? Cross a heterozygous smooth with a rough coat. What % of the offspring would be smooth?

What if there is more than one trait involved in the problem? Oh no!!!

Dihybrid Crosses Genotypes: For 2 traits, there will be 4 letters in the genotype (2 alleles per trait!) One trait (hair color) – BB “black”, Bb “brown”, bb “blonde” Two traits (hair color and earlobes) – BBEE, BbEe, BBEe, BbEE, etc. Phenotypes: Look at each letter group separately. Ex: BBEE genotype would have the phenotype of: “Black hair and Attached earlobes”

Gametes with Two Traits Determine Genotype of parent –Ex: BbEe (heterozygous for both traits) Determine the different combinations of hair color and earlobe alleles –Use the FOIL method!!! (First, Outer, Inner, Last) –BbEe genotype has gamete combos of: BE, Be, bE, be These are the allele possibilities found in egg or sperm.

Principle of Independent Assortment Mendel’s last principle During meiosis, alleles will align independently from each other to give the maximum possible gamete combinations.

Solving Problems STEP 1: Determine letters you will use to specify traits. STEP 2: Determine parent’s genotypes. STEP 3: Determine gametes from each parent STEP 4: Complete Punnett square cross and determine possible offspring. STEP 5: Determine phenotypic possibilities. Let’s Practice!!!!

A pure tall, pure green pea plant is crossed with a short, white pea plant. (Tall is dominant over short, green is dominant over white) 1.T = tall, t = short, G = green, g = white 2.Parents: TTGG x ttgg 3.Gametes: TG, TG, TG, TG and tg, tg, tg, tg 4.Punnett Square: 4x4 1.All offspring will be TtGg genotype which makes them all Tall and Green phenotype TG tg TtGg tg TtGg tg TtGg tg TtGg

A homozygous tall, heterozygous green pea plant is crossed with a heterozygous tall, heterozygous green pea plant. 2. Parents: TTGg x TtGg 3. Gametes: TG,Tg,TG,Tg and TG,Tg,tG,tg Tall/green: 12/16 or ¾Short/green: 0/16 Tall/white: 4/16 or ¼ Short/white: 0/16 TGTgTGTg TGTTGGTTGgTTGGTTGg TgTTGgTTggTTGgTTgg tGTtGGTtGgTtGGTtGg tgTtGgTtggTtGgTtgg

Two heterozygous tall and heterozygous green pea plants are crossed. 2. Parents: TtGg x TtGg 3. Gametes: TG,Tg,tG,tg and TG,Tg,tG,tg Tall/green: 9/16Short/green: 3/16 Tall/white: 3/16Short/white: 1/16 TGTgtGtg TGTTGGTTGgTtGGTtGg TgTTGgTTggTtGgTtgg tGTtGGTtGgttGGttGg tgTtGgTtggttGgttgg

Other Inheritance Patterns…dominant doesn’t always rule!

Incomplete Dominance A blending of the alleles forming a new heterozygous phenotype. Blending of phenotypes Neither allele is dominant. Ex: wavy hair, 4 o’clock flowers etc.

Ex: Incomplete Dominance In Jellyfish, there are yellow (Y) and blue (B) colors. Some end up green due to incomplete dominance. a.Cross a yellow and blue jellyfish P = YY x BB F1 = a.Cross a yellow and green jellyfish P = YY x YB

Codominance More than one allele is dominant, thus both are expressed in the heterozygous phenotype. Ex: speckled chickens, roan cattle, blood type, sickle-cell anemia

In chickens, white and black feathers are codominant. A heterozygous chicken is speckled with black and white feathers. a.Cross a speckled and black chicken.

Multiple Alleles Genes that have more than two alleles. More possible phenotypic characteristics. More possible genotypic combinations. Ex: rabbit fur color, human blood types.

A man who has blood type O marries a woman with type AB blood. What is the chance that their child will have a blood type of O?

Polygenic Traits Traits that are controlled by more than one gene. Ex: human skin color, eye color, body shape, height, intelligence etc.