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genetics

genetics. Chapters 11 and 14. GENETICS. The scientific study of heredity- how traits are passed down to offspring. TRAIT ---Specific characteristic ( blonde hair, blue eyes). GENE.

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genetics

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  1. genetics Chapters 11 and 14

  2. GENETICS • The scientific study of heredity- how traits are passed down to offspring TRAIT---Specific characteristic ( blonde hair, blue eyes)

  3. GENE • A hereditary unit consisting of a sequence of DNA that occupies a specific location (LOCUS) on a chromosome and determines a particular characteristic in an organism. (Genes undergo mutation when their DNA sequence changes)

  4. LOCUS (Loci plural) • Is a location on a chromosome where a gene occurs • Loci will be written as-----6p21.2 • 6- chromosome number • P- arm • 21.2- distance from centromere

  5. Chromosome map / IDIOGRAM • Detailed diagram of all the genes on a chromosome

  6. CHROMOSOME NUMBER • DIPLOID- cell that contains all the chromosomes of an organism (Humans= 46) • HAPLOID- cell that contains only HALF the chromosomes of an organism (ex- egg or sperm cell) (Humans=23)

  7. CHROMOSOMES SEX CHROMOSOMES- chromosomes that are responsible for determining sex of an organism (ex- X and Y in humans) AUTOSOMES- chromosomes that determine traits other than sex in an organism (ex- humans- chromosome 1-22)

  8. HOMOLOGOUS (PAIR) CHROMOSOMES pair of chromosomes that carry the same genes You will have one from each parent, they will both code for the same types of characteristics

  9. KARYOTYPE • a photograph that shows the complete DIPLOID set of chromosomes arranged in homologous pairs and arranged in order of decreasing size.

  10. ALLELE • Alternate forms of a gene/factor. • Examples: --brown eyes vs blue eyes --blonde hair vs brown hair --dimples vs no dimples

  11. Father of Genetics Gregor Mendel

  12. GREGOR MENDEL • An Austrian Monk (1822-1884) • Developed these principles without ANY scientific equipment - only his mind. • Tested over 29,000 pea plants by crossing various strains and observing the characteristics of their offspring.

  13. GREGOR MENDEL • Studied the following characteristics: 1. Pea color (Green, yellow) 2. Pea shape (round, wrinkled) 3. Flower color (purple, white) 4. Pod shape ( inflated, constricted) 5. Pod color (green, yellow) 6. Plant height (tall, short) 7. Flower position (axial, terminal)

  14. Mendel’s Experiments Mendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring. Mendel called these the P 1 generation. (pure bred, parental) X Short Offspring Purebred Short Parents X Purebred Tall Parents Tall Offspring

  15. Mendel’s First Experiment Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants. X Parent ShortP generation Offspring TallF1 generation Parent TallP generation Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

  16. Mendel’s Second Experiment Mendel then crossed two of the offspring tall plants produced from his first experiment. Offspring Parent Plants X TallF1 generation 3⁄4 Tall & 1⁄4 ShortF2 generation Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

  17. TERMS TO KNOW • MONOHYBRID CROSS- cross using only one trait • SELF CROSS- (SELF FERTILIZATION)- produce offspring asexually • P1 GENERATION-- parents- usually pure bred • F1 GENERATION- 1st set of offspring (1st family) • F 2 GENERATION- 2nd set of offspring (2nd family)

  18. Types of alleles • Dominant: An allele which is expressed (masks the other). • Recessive: An allele which is present but remains unexpressed (masked)

  19. PHENOTYPE vs GENOTYPE • Genotype: combination of alleles an organism has. (Ex- BB, Bb, or bb ) • Phenotype: How an organism appears. (Ex- brown hair, blonde hair )

  20. GENOTYPES • Homozygous: Both alleles for a trait are the same. (BB- homozygous dominant, bb homozygous recessive) • Heterozygous: The organism's alleles for a trait are different. (Carrier of the recessive allele) Bb

  21. Developed 3 laws LAW OF DOMINANCE- one allele always shows of the other LAW OF INDEPENDENT ASSORTMENT- states that each pair of genes (chromosomes) separate independently of each other in the production of sex cells. (example– you could have brown hair and blue eyes) LAW OF SEGREGATION-

  22. Mendel’s Law of Segregation Mendel’s first law, the Law of Segregation, has three parts. From his experiments, Mendel concluded that: 1. Plant traits are handed down through “hereditary factors” in the sperm and egg. 2. Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every trait. 3. The factors in a pair segregate (separate) during the formation of sex cells, and each sperm or egg receives only one member of the pair.

  23. Predicting offspring • Punnett square

  24. RR = red rr = white Rr = pink Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition. • Flower Color in 4 O’clocks

  25. R R r r Problem: Incomplete Dominance • Show the cross between a Red and a White flower. GENOTYPES: -RR (0), Rr(4); rr(0) PHENOTYPES: - pink (4); white ()

  26. R r Problem: Incomplete Dominance • Show the cross between a Pink and a Pink flower. GENOTYPES: - RR (1); Rr(2), rr (1) R r PHENOTYPES: • Red (1) pink (2); • white (1)

  27. NS = some of each SS = sickle cells NN = normal cells Codominance • The heterozygous condition, in which both alleles are expressed equally • Sickle Cell Anemia in Humans sick

  28. NS SS SS NS Problem: Codominance • Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. N S GENOTYPES: - NS (2) SS (2) - ratio 1:1 S S PHENOTYPES: - carrier (2); sick (2) - ratio 1:1

  29. Multiple Alleles • There are more than two alleles for a trait • Blood type in humans • Blood Types? • Type A, Type B, Type AB, Type O • Blood Alleles? • A, B, O (in book – IA, IB, I)

  30. AO AO BO BO Problem: Multiple Alleles • Show the cross between a mother who has type O blood and a father who has type AB blood. O O GENOTYPES: - AO (2) BO (2) - ratio 1:1 A B PHENOTYPES: - type A (2); type B (2) - ratio 1:1

  31. BO AB AO OO Problem: Multiple Alleles • Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood. GENOTYPES: A O • AB (1); BO (1); • AO (1); OO (1) • - ratio 1:1:1:1 B O PHENOTYPES: • type AB (1); type B (1) • type A (1); type O (1) • - ratio 1:1:1:1

  32. Dihybrid Cross:a cross that shows the possible offspring for two traits Coat Texture: R: Rough r: Smooth Fur Color: B: Black b: White In this example, we will cross a heterozygous individual with another heterozygous individual. Their genotypes will be: BbRr x BbRr

  33. Dihybrid Cross BbRr x BbRr First, you must find ALL possible gametes that can be made from each parent. Remember, each gamete must have one B and one R.

  34. Dihybrid Cross BbRr x BbRr Possible gametes: BR Br bR br Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…

  35. BR Br bR br BR Br bR br Dihybrid Cross BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth Then, find the possible genotypes of the offspring

  36. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Dihybrid Cross BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  37. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr How many of the offspring would have a black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  38. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr How many of the offspring would have black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? Phenotypic Ratio 9:3:3:1 Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  39. Chapter 12--Sex Linkage • All chromosomes are homologous except on sex chromosomes. • Sex chromosomes are either X or Y. • If an organism is XX, it is a female, if XY it is male. • If a recessive allele exists on the X chromosome. It will not have a corresponding allele on the Y chromosome, and will therefore always be expressed

  40. PEDIGREE ANALYSIS • is an important tool for studying inherited diseases • uses family trees and information about affected individuals to: • figure out the genetic basis of a disease or trait from its inheritance pattern • predict the risk of disease in future offspring in a family (genetic counseling)

  41. How to read pedigrees • Basic patterns of inheritance • 1. autosomal, recessive • 2. autosomal, dominant • 3. X-linked, recessive • 4. X-linked, dominant (very rare)

  42. How to read a pedigree

  43. female male affected individuals Sample pedigree - cystic fibrosis

  44. Autosomal dominant pedigrees 1. The child of an affected parent has a 50% chance of inheriting the parent's mutated allele and thus being affected with the disorder. 2. A mutation can be transmitted by either the mother or the father. 3. All children, regardless of gender, have an equal chance of inheriting the mutation. 4. Trait does not skip generations

  45. Autosomal dominant traits • There are few autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern ex. achondroplasia (a sketelal disorder causing dwarfism)

  46. AUTOSOMAL RECESSIVE 1. An individual will be a "carrier" if they posses one mutated allele and one normal gene copy. 2. All children of an affected individual will be carriers of the disorder. 3. A mutation can be transmitted by either the mother or the father. 4. All children, regardless of gender, have an equal chance of inheriting mutations. 5. Tends to skip generations

  47. Autosomal recessive diseases in humans • Most common ones • Cystic fibrosis • Sickle cell anemia • Phenylketonuria (PKU) • Tay-Sachs disease

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