Fundamentals of Genetics

1. Fundamentals of Genetics

2. Gregor Mendel • Mendel is considered the “father of genetics” • Genetics is the field of biology that studies how characteristics are transmitted from parents to offspring

3. Mendel’s Background • In 1842, Mendel entered a monastery in Austria & was given the task of tending to the garden • In 1851, he entered University of Vienna to study math & science • He then returned to the monastery—taught H.S. & kept a garden plot

4. Mendel’s Work • Mendel’s fascination with his garden & his knowledge of statistics led him to the study of heredity • Heredity is the transmission of characteristics from parents to offspring • Mendel is most famous for his experiments with garden peas

5. Mendel’s Garden Peas • Mendel observed 7 characteristics of pea plants • Each characteristic occurred in 2 contrasting traits

6. Pea Plant Characteristics 1. Plant height (long or short stems) 2. Flower position along stem (axial or terminal) 3. Pod color (green or yellow) 4. Pod appearance (inflated or constricted) 5. Seed texture (smooth or wrinkled) 6. Seed color (yellow or green) 7. Flower color (purple or white)

7. Pea Plant Characteristics

8. Mendel’s Methods • Mendel controlled how pea plants were pollinated • Pollination occurs when pollen grains produced in anthers (male repro part) are transferred to stigma (female repro part) • Self-pollination occurs when pollen is transferred from anthers of a flower to stigma of either same flower or flower on the same plant • Cross-pollination involves flowers of two separate plants • Most pea plants reproduce through self-pollination

9. Mendel’s Experiments • Mendel began by growing plants that were pure for each trait • Pure for a trait means it would always produce offspring with that trait • Strain refers to a plant that is pure for a specific trait • Mendel allowed plants to self-pollinate for several generations until he had a strain for 14 traits—called parental generation, P1

10. Mendel’s Experiment • Mendel then cross-pollinated the strain plants • Mendel called offspring of P1 generation the first filial generation, F1 generation • Then allowed flowers of F1 generation to self-pollinate • Mendel called offspring of F1 generation the second filial generation, F2 generation

11. Mendel’s Results • Mendel crossed a plant pure for green pods & one pure for yellow pods • Result produced a F1 generation of only green-podded plants

12. Mendel’s Results • Then allowed F1 generation to self-pollinate • F2 generation was 3/4ths green pods & 1/4th yellow pod

13. Mendel’s Conclusions • Mendel’s observations led him to hypothesize that something within pea plants controlled the characteristics he observed—called them factors • Mendel also hypothesized that each trait was inherited by means of a separate factor • Since the characteristics had two forms, he reasoned that there must be a pair of factors controlling each trait

14. Recessive & Dominant Traits • Whenever Mendel crossed strains, one of the P1 traits failed to appear in F1 plants • In every case, trait reappeared in ratio of about 3:1 in F2 generation • Led Mendel to conclude that one factor in a pair may prevent the other from having an effect • Dominant factor masks or dominates the other factor for a specific characteristic • Recessive factor is controlled by dominant factor

15. Law of Segregation • States that a pair of factors is segregated, or separated, during the formation of gametes

16. Law of Independent Assortment • Factors for different characteristics are distributed to gametes independently • Factors for different characteristics are not connected

17. Chromosomes & Genes • Molecular genetics is study of structure & function of chromosomes & genes • Chromosome is threadlike structure made up of DNA • Chromosomes occur in pairs • Gene is segment of DNA on a chromosome that controls a particular hereditary trait • Genes occur in pairs

18. Alleles • Allele refers to each of several alternative forms of a gene • Term replaces Mendel’s factors • Letters are used to represent alleles • Capital letters for dominant alleles • Example: G for green pod color • Lower case letters for recessive alleles • Example: g for yellow pod color • Two alleles for each trait • Dominant—Both capital or one capital, one lower-case • AA or Aa • Recessive—Both lower case • aa

19. Homozygous vs Heterozygous • Homozygous for a characteristic occurs when both alleles of a pair are alike • Homozygous dominant—AA • Homozygous recessive—aa • Heterozygous for a characteristic occurs when the two alleles in the pair are different • Heterozygous—Aa

20. Genotype vs Phenotype • Genotype refers to the genetic makeup of an organism • Consists of alleles that organism inherits from its parents • Phenotype refers to appearance of an organism as a result of its genotype

21. Probability • Probability is the likelihood that a specific event will occur • May be expressed as decimal, %, or fraction • Probability = # of times an event is expected to happen # of opportunities for an event to happen • Punnett squares aid in predicting the probability that certain traits will be inherited by offspring

22. Predicting Results of Monohybrid Crosses • Monohybrid cross is between individuals that involves one pair of contrasting traits • Punnett squares are used to predict the outcome of different types of crosses

23. Genotypic vs Phenotypic • Genotypic ratio refers to the ratio of genotypes that appear in offspring • Phenotypic ratio refers to the ratio of phenotypes that appear in offspring

24. Testcross • Recall that in humans, both RR and Rr result in right hand dominance. How might you determine whether the person is homozygous (RR) or heterozygous (Rr)? • Can perform a testcross • Testcross is when an individual of unknown genotype if crossed with a homozygous recessive individual • Used to determine the genotype of any individual whose phenotype is dominant

25. Complete Dominance • In Mendel’s pea plant experiments, one allele was completely dominant over another—referred to as complete dominance • In complete dominance, heterozygous individuals are indistinguishable from homozygous individuals • For example, PP and Pp would produce purple pea plant flowers

26. Incomplete Dominance • Incomplete dominance occurs when two or more alleles influence the phenotype, resulting in a phenotype intermediate between the dominant and recessive trait • Example: In certain flowers, 4 o’clocks, both alleles for red (R) flowers and allele for white flowers (r) influences the phenotype—neither allele is completely dominant over the other allele. If a red and white 4 o’clock cross-pollinates, the resulting offspring will be pink (Rr) • What if two pinks cross?

28. Co-dominance • Co-dominance occurs when both alleles for a gene are expressed in a heterozygous offspring • Neither allele is dominant nor recessive, nor do the alleles blend in phenotype • Example: A red coat horse (R) is crossed with a white coat horse (R’), result is a horse with roan coat color (RR’)

29. Roan Horse

30. Dihybrid Cross • Dihybrid cross is a cross between individuals that involves two pairs of contrasting traits • Punnett squares now have 16 blocks