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WHAT IS GENETICS?. GENETICS is the study of how traits are passed from parent to offspring in the form of Genes. HISTORY! Gregor Mendel. Born 1822 Austrian Monk Examined reproduction of pea plants. Plants reproductive organs are called FLOWERS A flower has both male and female parts.

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  1. WHAT IS GENETICS? • GENETICS is the study of how traits are passed from parent to offspring in the form of Genes.

  2. HISTORY!Gregor Mendel • Born 1822 • Austrian Monk • Examined reproduction of pea plants

  3. Plants reproductive organs are called FLOWERS • A flower has both male and female parts. • The pea plants Mendel was working with were typically TRUE-BREEDING, meaning they self-pollinated • EX, TALL pea plants would always be pollinated by tall pea plants and produce tall offspring!

  4. WHAT WE KNOW (MENDEL DIDN’T) Genes– control a heritable feature (characteristic); Example: Hair color, seed shape, height; Allele – controls the variation of a feature (trait). Example: brown, blonde, black hair

  5. REVIEW TIME: What are homologous chromosomes???

  6. Homologous chromosomes may…… • Both have the same alleles HOMOZYGOUS (aka: pure or true-breeding) • Both have different alleles  HETEROZYGOUS (aka: hybrid)

  7. Mendel’s Idea • Cross two pea plants with different contrasting traits! • Ex: • First cross : Crossed true breeding purple with true-breeding white plants. • Called offspring F1 Generation • Results were that offspring were_100% PURPLE_ • Had the white allele disappeared????

  8. Mendel’s Law of Dominance • some alleles over power others. So even if both alleles are present, we only “see” the dominant one. • the “hidden” allele is called recessive • This only applies to SOME genes, not all

  9. Second cross  two of the purple F1 Offspring Called offspring the F2 Generation Results • 75 % purple • 25 % were white • White trait had reappeared!

  10. “The Traits (genes) Mendel looked at

  11. Mendel’s Law of Segregation • during meiosis, the pair of alleles in a parent will separate. • Only ONE allele for EACH TRAIT will pass from each parent to the offspring

  12. Ex. sugar beet preference. • dominant allele (A) prefers sugar beets • recessive allele (a) does not. • Heterozygote produces gametes • 50% chance • Get A • Get a Question: If a heterozygous sugar beet eater marries a non-sugar beet eater, what possible offspring could they have?

  13. Mendel’s Law of Independent Assortment • Alleles for different genes are passed to offspring independently of each other. • The result is that new combinations of genes present in neither parent is possible. • How many allele combinations could the following genotype produce? • RRYY • RRYy • RrYy

  14. Genetic Terms • Diploid (2n)- Two sets of chromosomes. • Somatic Cells • Haploid (n)- One set of homologous Chromosomes • (gametes) • Egg- Female haploid gamete • Sperm- male haploid gamete

  15. Parent – Seriously, you should know this Meiosis – Cell division that produces haploid gametes Testes – Site of male meiosis Gamete – Haploid sex cell (sperm, egg, pollen)

  16. Zygote- Single cell (result of sperm and egg) Progeny - Offspring Offspring – see above Fertilization – gametes fuse into zygote Ovary- site of female meiosis - eggs

  17. Genotype: the alleles that an organism has. • alleles are abbreviated using the first letter of the dominant trait. • capital letter represents the dominant • ex: P for purple flower allele • lower case represents the recessive.  • ex: p for white flower allele

  18. All diploid organisms have two alleles for each trait: • Can be two of the same allelesEx: PP or pp called Pure or Homozygous. OR • Can be two different alleles  • Ex: Ppdescribed as Hybrid or Heterozygous

  19. Phenotype: physical appearance • Examples: brown hair, widows peak, purple flowers • the trait that “wins” in the case of complete dominance; • depends on the combination of alleles GENOTYPE

  20. MENDEL’S CROSSES • P Generation: “parents;” • F1 Generation  offspring of P generation • F2 Generation  offspring of F1 generation Punnet Squares  How we show allele combinations in crosses

  21. Allele in Egg 2 Allele in Egg 1 Zygote formed if sperm 1 fertilizes egg 1 Zygote formed if sperm 1 fertilizes egg 2 Allele in sperm 1 Allele in sperm 2 Zygote formed if sperm 2 fertilizes egg 1 Zygote formed if sperm 2 fertilizes egg 2

  22. Monohybrid CrossTall vs. Short Example • Tall allele  T Short allele  t • P Cross TT x tt • F1 Generation • Genotypes • Phenotypes T T t t

  23. F2 Generation F1 Generations 100% Tt Tt x Tt F2 Generation Genotypes- Ratio = Phenotypes- Ratio = T t T t

  24. Sample Problems • Homozygous Tall x Heterozygous Tall • Heterozygous Tall x Homozygous Short

  25. Probability • Probability is only the LIKELIHOOD of an event happening. • It does not mean it is what HAS to happen • Ex. Coin Toss. Two tosses, always one heads and one tails? • What happens when we look at very large samples? • Ex. Male/female ratio of a family vs. the world!

  26. INHERITENCE PATTERNS • Every gene demonstrates a distinct phenotype when both alleles are combined (the heterozygote) • Complete dominance is when both alleles are present, only the dominant trait is seen. • Incomplete dominance - when both alleles are present, the two traits blend together and create an intermediate trait


  28. Inheritance Patterns: Co-dominance - when both alleles are present, both traits are visible Different notation: Use first letter of the feature with a superscript for the trait. Example: CW or CR for white petals or red petals;

  29. Women have two X’s but men only have one. How do we deal with the genes on the X chromosome?

  30. Probabilities • Question 1: What is the probability of having a female offspring? • Question 2: After having 4 sons in a row, what is the probability the next kid will be male? • Question 3: What is the probability of having three daughters in a row?

  31. Sex-Linked Traits • Refers to traits coded by genes found on the X chromosome • Females will have 2 copies of these genes • Males will have 1 copy of these genes • Significance??? • If males get a bad (recessive) allele for a sex-linked trait, THEY WILL EXPRESS THE RECESSIVE TRAIT!

  32. Example – Color Blindness • Seeing color (XC) is dominant to being color blind (Xc) • Identify the sex and trait of the following: • XCY XCXc XCXC • XcXc XcY

  33. XC XC XC Xc Xc Y XC Y Cross Number 1: What % chance of having color blind daughter? Son? XC Xc XC Y


  35. Test cross: a cross that determines genotype of dominant parent - Cross unknown dominant parent (possibilities BB or BB) with a recessive parent then analyze the offspring. Ex. B- Black Hair b- white hair You are given a black-haired guinea pig and need to determine whether homozygous dominant or heterozygous.

  36. Multiple Alleles • Genes may have more than two alleles.

  37. Multiple alleles: Some genes have more than two variations that exist, although we still only inherit 2 Example: Human blood types Three alleles: IA IB i

  38. Polygenic – • Multiple genes code for a trait each with 2 alleles • Examples in humans: • Skin Color • Eye Color • Height • Why so many possibilities??? SKIN PIGMENTATION

  39. Dihybrid cross: A cross that focuses on possibilities of inheriting two traits - two genes, 4 alleles Black fur is dominant to brown fur Short fur is dominant to long fur What is the genotype of a guinea pig that is heterozygous for both black and short fur?

  40. Dihybrid cross: Parent phenotypes: BbSs x BbSs Figure out the possible gametes: Then set up punnett square

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