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DNA and Mendelian Genetics: Understanding Traits Inheritance

Explore the fascinating world of genetics and DNA, and learn how traits are inherited through Mendelian genetics. Discover the role of DNA, genes, chromosomes, alleles, and the principles of probability using Punnett squares. Find out how these factors shape who we are and control every aspect of our lives.

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DNA and Mendelian Genetics: Understanding Traits Inheritance

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  1. GENETICS Honors: Ch. 9Academic: Ch. 11

  2. DNA-What makes you YOU? • DNA is a system of codes that controls every aspect of your life (how you look, how you act, etc.) • DNA is like the instruction manual to keep you working.

  3. DNA What are sections of DNA known as? (Hint-they code for a protein) • DNA gene • Gene = one section of DNA that controls one specific trait. (Ex. Hairline gene, earlobe gene, etc.)

  4. DNA • Chromosome = 1 strand of DNA that is condensed/squeezed into a rod shape

  5. GENETICS

  6. Mendelian Genetics Essential Question: “How can 2 brown rabbits have a white fur baby?” Genetics is the scientific study of how traits are inherited from one generation to next. Heredity = biological inheritance

  7. Mendel was a monk in the 1800’s • He was in charge of the monastery garden. • He performed experiments breeding pea plants. Gregor Mendel - “Father of Genetics” Gregor Mendel    1822-1884  

  8. Mendel knew an important fact of his pea plants: The flowers of plea plants have both male and female reproductive parts. Pea plants have the ability to: • #1 Self Pollinate= the sperm cells in the pollen fertilize the egg cells in the same flower. • Aka TRUE Breeding- creates identical versions of parents. • #2 Cross-pollinate= fertilization between 2 plants (1 plant’s egg cells & another plant’s pollen (sperm).

  9. Mendel grew garden peas to see how characteristics were inherited. • He looked at 7 traits that are easily recognized and only occur in 1 of 2 traits. Traits= a specific characteristic, such as seed color or plant height.

  10. Mendel’s 1st Experiment • Mendel crossed 2 plants with contrasting traits together. • Round pea plant x a wrinkled pea plant • These plants are called the Parental or “P” generation

  11. Mendel’s Experiment: Results RR rr • The result of the cross= the “F1” (filial 1 generation). • These offspring= hybrids ??? Hybrids- a mix of the 2 characteristics Questions: • #1 What were the F1 generation like? • #2 Did the characteristics of the P generation blend?

  12. Mendel’s Experiment: Results RR rr • He observed that ALLthe offspring in the F1 generation had the trait of only 1 of the two parents. Rr Question: • #1 What happened to the characteristics that "disappeared”?

  13. Mendel’s Experiments rr RR • Mendel allowed the “F1” hybrid generation to self pollinate and produce an F2 generation (second filial). Rr • He found that in the F2 offspring of this mating the recessive alleles reappeared.

  14. Mendel’s Experiment • Mendel mated a PURE purple with a PURE white flower= cross fertilization. • P generation= • F1 generation= • F2 generation= What do you think offspring (F1) look like??

  15. Mendel’s Experiments What do you think offspring (F2) look like??

  16. Thank you Mendel! • Based on his experiments we found: • There are alternative forms of genes he called factors(today we call these alleles) Alleles- alternative form of a gene

  17. Alleles: PHENOTYPE: The physical traitthat you actually see on the person. example: Tall, Purple, Round GENOTYPE: The alleles (letters)on the gene example: Tt, Pp, RR

  18. Thank you Mendel! • For each characteristic an organism has 2 alleles – one from each parent • If these 2 alleles are the same we call it homozygous • If these 2 alleles are different we call it heterozygous Homozygous-both pairs of genes for a specific trait are the same. Heterozygous- both pairs of genes are different

  19. Thank you Mendel! • When 2 alleles are different, the 1 that is expressed is dominant, while the one that is hidden is recessive. Dominant Allele- mask/hides the other allele. Recessive Allele- the allele is hidden unless there are 2 copies of the recessive allele.

  20. Thank you Mendel! • Law of Segregation= Independent Assortment during Meiosis I (Metaphase I) • Genes are segregated/separated from each other when gametes are formed.

  21. Results Thank you Mendel! By breeding many plants over and over, he found that "statistically" certain traits appeared with a certain probability

  22. Probability & Punnett Squares • Probability- the likelihood that a particular event will occur. • The way alleles segregate in an organism is completely random- like a coin flip so the principles of probability apply If we flip a penny 20 times How many times should you get heads? How many times should you get tails? Let’s see if you are correct!! TAKE OUT A COIN!!!

  23. Probability & Punnett Squares • Punnett Square is used to determine the possible gene combinations that could result from a genetic cross. PUNNET T VID

  24. How To… Making a Punnett Square

  25. Punnett Squares • Monohybrid Crosses- A cross between individuals that involves 1 pair of contrasting traits

  26. Punnett Squares What pattern do you see? Genotype: 100% Xx Phenotype: 100% Dominant Trait

  27. Punnett Squares What pattern do you see? Genotype: 25% XX, 50% Xx 25% xx Phenotype: 75% Dominant trait 25% Recessive trait

  28. Punnett Squares Determine the Genotype & Phenotype for #1,#2,#3 & just the genotype for #4 T t R R Genotype: 100% RR Phenotype: 100% Round seed coat shape Genotype: 25% TT, 50% Tt, 25% tt Phenotype: 75% Tall plant 25% short plant T R t R Genotype: 25% rr, 50% rw, 25% ww Phenotype: Can’t determine w/ the table sorry!! r w b b r b Genotype: 100% bb Phenotype: 100% white seed coat w b

  29. Punnett Squares Determine the Genotype & Phenotype g g G g G Genotype: 100% Gg Phenotype: 100% Green pod color G G

  30. Punnett Squares

  31. Continuing Mendelian Genetics Question: • Do genes segregate together or separately? • Mendel conducted an experiment which followed 2 traits at a time: • Crossed a homozygous yellow/round pea plant (YYRR) with a homozygous green/wrinkled pea plant (yyrr) • The F1 generation produced ALL yellow/round pea plants (YyRr)

  32. RRYY Dihybrid Crosses __ __ PLEASE FILL IN YOUR PUNNET SQAURE! __ __ __ __ __ __

  33. Dihybrid Crosses PLEASE FILL IN YOUR PUNNET SQAURE!

  34. Continuing Mendelian Genetics Question: • Do genes segregate together or separately? • Mendel then used the F1 plants and self pollinated RrYy x RrYy: • He found that alleles segregated independently – use the FOIL (first-outer-inner-last) method to figure out all of the possible combinations of alleles from one parent: • RY • Ry • rY • ry RrYy= RY RyrYry

  35. This is known as a….. • Dihybrid Crosses- A cross between individuals that involvesTWO pairs of contrasting traits. Black fur? Black eyes? Red eyes? Black fur & black eyes? Black fur & red eyes? Monohybrids (one trait) Dihybrids (two traits) & means multiply!

  36. P Generation= AaBb vs. AaBb Dihybrid Crosses AaBb= AB AbaBab FOIL your gametes to figure out what goes in the columns and rows

  37. Dihybrid Crosses ssyy= sysysysy SsYy= SY SysYsy

  38. Dihybrid Crosses P Generation= EeTt vs. EeTt

  39. P Generation= AaBb vs. AaBb Dihybrid Crosses AaBb= AB AbaBab FOIL your gametes to figure out what goes in the columns and rows

  40. Dihybrid Crosses ssyy= sysysysy SsYy= SY SysYsy

  41. Dihybrid Crosses P Generation= EeTt vs. EeTt

  42. Exceptions to Mendel’s Rules Beyond Dominant and Recessive Alleles • Complete Dominance • Incomplete Dominance • Codominance • Multiple Alleles • Polygenic • Sex Linked

  43. Exceptions to Mendel’s Rules Beyond Dominant and Recessive Alleles • Complete Dominance • Incomplete Dominance • Codominance • Multiple Alleles • Polygenic • Sex Linked

  44. 1. Complete Dominance • One allele can completely hide the other • Mendel traits

  45. 2. Incomplete Dominance • When 2 or more alleles influence the phenotypeand the heterozygous phenotype is a blendof both homozygous phenotypes. • BOTH alleles affect the Phenotype • BLEND

  46. Incomplete Dominance Example: The trait for fur color in mice is controlled by two alleles. W for white and w for black. The intermediate phenotype is grey. Cross a grey mouse with a white mouse. What is the probability the offspring will be white?

  47. 3. Codominance • When both alleles for a gene are expressed in a heterozygous offspring the trait. • No Blending. • BOTH traits are expressed.

  48. Codominance Example: • Two tulip plants are mated one has yellow petals and the other has red. All the offspring of these flowers have both red and yellow petals. What are the genotypes of the parents and the offspring? = RR =YY = RY

  49. 4. Multiple Alleles • A trait that is controlled by three or more alleles that can fit into one gene.

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