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WHY DO WE LOOK THE WAY WE ARE?

WHY DO WE LOOK THE WAY WE ARE?. WHAT IS GENETICS?. Genetics is the scientific study of heredity. Heredity is the passing of characteristics ( traits) from parents to offspring. Traits vary among individuals. Traits are determined by genes .

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WHY DO WE LOOK THE WAY WE ARE?

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  1. WHY DO WE LOOK THE WAY WE ARE?

  2. WHAT IS GENETICS? • Genetics is the scientific study of heredity. • Heredity is the passing of characteristics (traits) from parents to offspring. • Traits vary among individuals. • Traits are determined by genes. Ex.- Your eyes are determined by a specific gene. • Alleles are different forms of one gene. Ex.- An allele for blue eyes and an allele for brown eyes

  3. HOW DO WE KNOW GENES EXIST? GREGOR MENDEL- 1865 • Austrian Monk • The father of genetics. • Famous study of pea plants • Crossed pea plants with different traits. Ex.- height, seed color, seed shape • Observed that there are factors controlling each trait.

  4. DEFINITIONS • Punnett Squares are diagrams used to predict genetic crosses. • Individuals with identical alleles are called homozygous • Individuals with different alleles are called heterozygous • Phenotype – physical characteristic • Genotype – genetic makeup

  5. HOW TO USE PUNNETT SQUARES • Choose a letter to represent the alleles in a trait. • Write the genotypes of the parents. • Write one parents alleles above the Punnett Square, one letter for above each box. • Write the other parents alleles on the side on the Punnett Square, one letter for each box. • Fill in the 4 boxes with the possible combinations. B B • Ex.-Genotypes BB and Bb B b

  6. PUNNETT SQUARE Trait for eye color B B Mother has BB genes Father has bb genes b Uppercase B is dominant lower case b is recessive b Homozygous Brown color= BB Homozygous Blue color = bb Heterozygous =Bb GENOTYPE =Bb PHENOTYPE= BROWN EYES

  7. DEFINITIONS • Sexually reproductive- requires 2 organisms that make gametes to produce offspring. • Gamete – A sex cell needed for reproduction. • Female gametes- eggs • Male gametes- sperm • Segregate- to move apart or seperate.

  8. MENDEL’S PRINCIPLES The inheritance of biological characteristics are determined by genes. For two or more forms of a gene, dominance and recessive forms may exist. Most sexually reproductive organisms have two sets of genes that separate during gamete formation. Alleles segregate independently.

  9. Look at the Punnett Square to answer these questions: • How many alleles does each parent have for eye color? • What are they? • How many alleles does each parent pass to its offspring? • What are they? B B b b

  10. Look at the Punnett Square to answer these questions: • How many offspring will have blue eyes? • What is the percentage of offspring that are Homozygous for eye color? • What is the percentage of offspring that are heterozygous for eye color? B B b b

  11. Consider this… • Alleles are different types of a gene. • Genes determine traits. • Traits are our genotypes and phenotypes. • Genes are located on our chromosomes. • Chromosomes contain all of our genetic information. • Parents pass their chromosomes onto their offspring. • Homo sapiens, (Humans), have 46 chromosomes.

  12. HUMANS HAVE 46 CHROMOSOMES • HOW CAN EACH PARENT PASS TRAITS TO THEIR OFFSPRING? • CAN OFFSPRING HAVE MOM’S 46 + DAD’S 46? • CAN OFFSPRING HAVE 92 CHROMOSOMES?

  13. LAW OF SEGREGATION • Humans have 46 chromosomes. • Genes are located on chromosomes. • 23 chromosomes come from each parent. • 22 chromosomes determine traits. • 1 chromosome determines gender (male or female).

  14. The Principle of Dominance • The principle of dominance states that some alleles are dominant and others are recessive. • Dominant alleles are always expressed. • Recessive alleles are only expressed if both alleles are recessive. Dominant means to be expressed. Recessive means to be hidden.

  15. Beyond Dominant and Recessive Dominant and Recessive traits are not the only way to produce a phenotype. Other ways phenotypes are produced are through: • Incomplete Dominance • Codominance • Multiple Alleles • Polygenetic traits

  16. What do you think incomplete dominance means? HINT: Incomplete Dominance – One allele is not completely dominant over the other. Ex.-White flower crosses with a red = pink flower.

  17. What do you think codominancemeans? HINT: Codominance – Both alleles contribute to the phenotype. Ex.-Red cow X White Cow = Roan Cow.

  18. What does multiple alleles suggest when considering a phenotype? HINT: Multiple Alleles – More than two alleles control the phenotype. Ex.- Coat color of rabbits.

  19. What do you think polygenic traits means? HINT: Polygenic traits – Several genes control the trait. Ex.-Skin color in humans.

  20. ACTIVITY: STUDY THE CHART AND LIST ONLY THE EXPRESSED TRAITS FOR YOURSELF.

  21. HOMEWORK • Take out your Family Trait Chart. • Use a pencil for this activity. • Complete the Punnett Square worksheet. • Create a Punnett Square for each trait. • From your data determine your parents second allele for that trait. Their geneotype. • Be prepared to discuss your results and any problems you encountered.

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