Intro to Genetics

1. Intro to Genetics Chapter 11

2. 11.1 The Work of Gregor Mendel • Heredity is the transmission of genetic info from one generation to the next. • Genetics is the branch of biology that seeks to explain inherited variation. It is the science of heredity.

3. The “father of heredity” was Gregor Mendel (1822-1884), a monk who worked with pea plants in Austria • His model organism was the ordinary pea plant, which he conducted tests on and observed for 8 years

4. Pea flowers can be self-pollinating(they can fertilize themselves). • cross-pollination is when pollen (contains sperm) is transferred from the anther of one plant to the stigma (female part containing eggs) of another • truebreeding plants are those that produce plants identical to the parent plants in every generation (they are genetically pure)

5. A trait is a specific characteristic that varies from one individual to another. • Mendel studied seven pea plant traits, each with two contrasting characteristics. • He crossed plants with each of the seven contrasting characteristics and studied their offspring.

6. P = parental generation • F1 = first offspring / 1st filial generation • F2 = second offspring / 2nd filial generation (grandchildren) • Example: • P: Green (GG) x Yellow (gg) pods • F1: all green pods … what happened to all of the yellow ones? • F2: ¾ green, ¼ yellow – • written as a ratio 3:1

7. Mendel proposed that organisms had 2 copies of a “Factor” for a particular trait, one from each parent that remain separate • today we call the “factors” genes • alleles = the alternate forms of genes • dominant allele = the trait that is visible, when that allele is present – it is represented by a capital letter • recessive allele = the trait that is masked by the dominant trait – it is represented by the lowercase of the same letter

8. Mendel suggested that alleles separate, or segregate, from each other during gamete formation • This is why we saw all green pea pods in the F1 generation, but then saw yellow pods reappear in the F2 generation

9. Human Traits:

10. 11.2 Probability and Punnett Squares • Probability is a branch of math that predicts the chances that a certain event will occur • flip a coin: 50/50 chance of getting heads • drawing an ace: 4/52 or 1/13 • each event is independent of the next • every child born is ½ or 50/50 • The principles of probability can be used to predict the outcomes of genetic crosses.

11. Punnett squares can be used to predict and compare the genetic variations that will result from a cross. • dominant allele for tall represented by T • recessive allele for short represented by t • homozygous = when both alleles are the same (TT, tt) • heterozygous = when the alleles are different (Tt)

12. genotype = the genetic makeup of an individual (TT) • phenotype = what it physically looks like (tall plant)

13. Probabilities Predict Averages • Probabilities predict the average outcome of a large number of events. • Probability cannot predict the precise outcome of an individual event. • In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

14. 11.3 Exploring Mendelian Genetics • monohybrid cross = crossing organisms that differ in only 1 trait • Green peas x yellow peas • pea plants are diploid, so they have 2 alleles for each gene

15. dihybridcross = crossing individuals that differ in 2 traits • round, yellow seeds x wrinkled, green seeds • RRYY x rryy • principle of independent assortment = alleles for 1 trait segregate independently of alleles for other traits during gamete formation • genes for seed shape & color separate independently

16. F2 generation: 9:3:3:1 ratio • 9 round, yellow: 3 round, green: 3 wrinkled, yellow: 1 wrinkled, green • all of Mendel’s findings using pea plants apply to humans

17. Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. • incomplete dominance = when the phenotype of a heterozygote is an intermediate between the two parents • red x white snapdragons = all pink • different letters are used to represent this condition • C = color CR = red Cr = white

18. codominant = when both phenotypes appear in heterozygotes • example: roan coat color, black & white chickens and blood type • also represented with different letters

19. multiple alleles = more than 2 alleles for a trait • example: blood type, coat color in labs

20. KEY C = full color; dominant to all other alleles cch= chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles • Different combinations of alleles result in the colors shown here. Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch AIbino: cc

21. Traits controlled by two or more genes are said to be polygenic traits. • Skin color, hair color • Characteristics of any organism are determined by the interaction between genes and the environment. • height, weight, intelligence • hair color, eye color, skin color • heart disease, cancer, schizophrenia