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Mendel Genetics

Mendel Genetics. Our Main Man Mendel!. Gregor Mendel  father of genetics; discovered trends in heredity 30 years before other scientists! Prior to Mendel what did people believe about inheritance? Blending Theory  all genetic traits are equally mixed in offspring

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Mendel Genetics

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  1. Mendel Genetics

  2. Our Main Man Mendel! • Gregor Mendel father of genetics; discovered trends in heredity 30 years before other scientists! • Prior to Mendel what did people believe about inheritance? • Blending Theory all genetic traits are equally mixed in offspring • If this were true what would disappear? • Outliers (really tall, short, etc… members of a population)

  3. Mendel’s Work • Secret to Mendel’s discovery is his detailedrecord keeping and attention to the controlled experiment • What was his model species? • Garden peas • What did this species work so well? • Easily grown; has set traits (characteristics) that are easily to observe; character differences mostly in twos (white flowers vs. purple; tall vs. short)

  4. 7 Traits of Mendel’s Experiments

  5. If you are going to observe trait inheritance, what must you be pretty sure of? The genetic make up of your subjects Pollination- transfer of pollen (male gametes) to the female reproductive organ in plants To make pure-breeds for each trait Cross-pollination- using pollen from a plant with different traits to test the trait inheritance patten

  6. Mendel’s Monohybrid Crosses Wanted to produce specific hybrids of plant with different traits Tall X Short Purple Flowers X White Flowers Green Seeds X Yellow Seeds Started with P1 Parents Offspring were call F1 Filial (son/daughter) 1st generation F1 XF1 = F2 2nd generation

  7. 3 1

  8. Controlling Heredity Each organism has two factors that control each of its traits. Genes exist in alternative forms. We call these different gene forms alleles Alleles are located in the same locus (area) of homologous chromosomes (chromosome sets) Allele that determines the appearance (phenotype) is dominate Other allele is recessive Genotypes : Homozygous dominate AA Homozygous recessive aa Heterozygous Aa

  9. Alleles are RR, YY, PP, TT or Rr, Yy, Pp, Tt… Alleles are rr, yy, pp, tt, etc…

  10. Mendel’s Three Theories • From the first cross all F1 flowers are purple • From F1 cross 3 purple:1 white flower • Theories • The parents must carry a pair of factors (alleles) the control the inheritance of each trait • P purple flowers • p white flowers • If you have one of each allele, one will be dominate and one recessive • Pp purple flowers • Pairs of alleles are segregated into different gametes • Law of Segregation • Gamete has either P or p

  11. Punnett Squares • Reginald Punnett; English biologist • Monohybrid crossfollowing the crossing of parents while focusing on 1 trait • A cross with 1 homozygous dominate and 1 homozygous recessive makes what? • Only heterozygous offspring • A cross between 2heterozygous produce what? • ¼ TT, ¼ tt, and ½ Tt

  12. Monohybrid Crosses • Punnett Square method for organizing alleles during breeding that uses statics • All Statics probabilities are between 0-1 • 0impossible • 1 completely possible • Product Rule events where both A and B will occur • Chance of heads vs. tails 0.5 • Chance of heads twice 0.5x0.5= 0.25 • Sum Rule when two or more possible ways exist to get the same outcome • Chance of getting head and tail in 2 tosses 0.5x0.5=0.25 • Two ways (head and tail or tail and head) 0.25+0.25= 0.5

  13. Practice Crosses • What are the possible genotype ratios for a cross between homozygous dominate (purple) and homozygous recessive (white) garden pea plants? What is their phenotypes? • 1.0 chance of heterozygous (Pp) • All purple flowers • What are all possible genotype ratios for a green seed X yellow seed? Green is dominate. • 1.0 chance heterozygous (Pp) • 0.5 chance heterozygous (Pp) and 0.5 homo recessive (pp) • All green seeds; half green and half yellow seeds

  14. Genetic Terminology • What is a genotype? • Allele pairing in genes • What is a phenotype? • Physical appearance of alleles • Word for AA genotype? • Homozygous dominant • Word for aa genotype? • Homozygous recessive • Word for Aa genotype? • Heterozygous • What do you call a cross between two subjects that follows the inheritance of onetrait? • Monohybrid Cross

  15. Dihybrid Cross • Cross following two traits with both subjects being heterozygous for each trait (AaBb X AaBb) • What ratio does a dihybridcross always produce? • 9:3:3:1 • 9 AB; 3 Ab; 3 aB; 1 ab • What does this ratio tells us about alleles for A and B? • They each sort randomly into gametes (not linked) • Principle of Independent Assortment

  16. Practice Crosses • What is ratio of the phenotypes of a RRYy x Rryy? • R round seed • r wrinkled seed • Y yellow seed • y green seed • 1.0 round seed; 0.5 yellow and 0.5 green seed • What phenotype will not be present after a Rryy x rryy cross? • Yellow seeds

  17. Chromosome Theory of Inheritance • Sum up what we have learned from Mendel: • Chromosomes occur in pairs in sexually reproducing, diploid organisms. Alleles for each gene are on these chromosomes • The chromosomes of each pair are separated and delivered to different gametes. This also separates alleles of genes • The separation of any pair of chromosomes in meiosis and gamete formation is independent • One member of each chromosome pair after fertilization comes from the male and female parents

  18. Alternative Inheritance Patterns • Incomplete dominance • Phenotype for heterozygous genotype is a blend of both homogenous traits • Recessive trait is not completely blocked because dominate trait is incomplete • CRCR x CWCWgive what type of offspring ratios? • 100% pink (heterozygous) • What about F2? • 1 Red: 2 Pink: 1 White

  19. Alternative Inheritance Patterns 2) Codominance • Both alleles are expressed equally and produce equal effects in heterozygotes • MN blood groups • People either have M form glycoproteins or L form glycoproteins • If you get both alleles you have both glycoproteins • Same inheritance patterns as incomplete dominance

  20. Alternative Inheritance Patterns 3) Multiple Allele Inheritance • Several types of same allele will code for different phenotypes • Human Blood-Types • Allele I-> IA, IB, or i IBIB IAIA IAIB ii

  21. Alternative Inheritance Patterns 4) Epistasis gene interaction; genes on one allele hide the phenotypes of genes on another allele • Common in skin tones and animal colors • B and C allele produce dark pigments while b and C produce less/no pigment • B and C needed to make black • C needed to make brown if b • No C means white regardless of B or b

  22. Alternative Inheritance Patterns 5) Polygenic Inheritance • Several genes contribute to the same trait (quantitative trait); skin color, height, weight, etc… • Typically shows bell-curve distribution in a population

  23. Sex Chromosomes • Sex determination • chromosomes, which determine the sex of an individual, are called sex chromosomes • 22 other chromosomes are called autosomal chromosomes

  24. Sex-Linked Inheritance • Drosophila eye color: • “Wild type” Red, w+w+ • Mutation White,ww • R dominate over r • What is the F1 genotype? • heterozygous; w+ w • What is the F2 ratio? • 3:1 1 w+w+, 2 w+ w, 1 ww • F2 only produces males with white eyes • Sex-linked inheritance

  25. Sex-linked Inheritance • Y Chromosome • Sex-determining genes; SRY gene makes females into males while an embryo • Maybe fading from existence; may be getting smaller • XY heterogametic • X Chromosome • Mostly codes for non-sex related traits (ex. Color vision) • XXhomogametic • Colorblindness • Hemophilia • Low platelet number makes it difficult to stop bleeding • Influences a revolution in Russia

  26. Too Many Xs! • Why do females need two Xs? • They Don’t! Two X chromosomes would mean double the genetic material necessary • What does the body do with the X chromosome? • It randomly shuts one X down • Creates a Barr body dense mass of inactive chromatin • They are copied and passed on in mitosis but are never used for proteins • How can this show us X-recessive traits? • Dominate X might be randomly deactivated so the X recessive is randomly present in cells • Female calico cats have a mix of orange and black fur but males are always black or orange

  27. Environmental Effects • Environmental Factors: • Temperature, nutrition, light, etc… can effect the phenotype of an individual by changing the expression of the genes • Arctic animals are influence by cold • Internal Factors: • Hormones regulate gene expression so a genotype may not express the same phenotype it different individuals • Peacock color is not sex-linked, but the gene that regulates the color gene is

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