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Understanding Genotype and Phenotype Relationships in Genetics

This educational resource explores the critical relationship between genotype and phenotype, focusing on how genetic traits are inherited from parents. It covers fundamental concepts such as heredity, the law of segregation, and the use of Punnett squares to predict genetic outcomes in monohybrid and dihybrid crosses. Students will learn how traits are passed down through chromosomal inheritance while also considering environmental influences. Engaging examples and questions will encourage deeper understanding and application of genetic principles in predicting inheritance patterns.

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Understanding Genotype and Phenotype Relationships in Genetics

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  1. Introduction to genetics -Part II Mrs. Stewart Honors Biology Central Magnet School

  2. Bell work Describe the relationship between genotype and phenotype

  3. Standards • CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids. • CLE 3210.4.3 Predict the outcome of monohybrid and dihybrid crosses.

  4. objectives • Analyze the law of segregation • Create a punnett square using the genotypes of parents • Predict the outcome and probability of monohybrid crosses

  5. Decide with your partner

  6. What is Heredity? • Why do children look like their parents? • Why do brothers and sisters resemble each other? • We inherit traits from our parents • Heredity = the passing of genetic traits from parents to offspring

  7. Traits and genes • Genes carry the instructions that define our traits • Genes = segments of the DNA sequence that code for a particular trait • Traits = genetically determined characteristics (qualities) • Example: natural hair color, eye color, skin tone, etc. • The environment we live in can also help define our traits • Example: a person’s genes may code for a certain hair color, but exposure to dyes, chemicals, sunlight, etc can change that color • Characteristic = can be altered by the environment

  8. Dogs • Tell your CAT another example of a characteristic – (a trait that can be altered by the environment)

  9. How do we get traits from our parents? • Human body cells (somatic cells) have 2 complete sets of 23 chromosomes • 2 x 23 = 46 chromosomes • One set of 23 comes from sperm (Dad) • One set of 23 comes from egg (Mom) • Each parent contributes one complete set to the child, giving the child a “mix” of genes

  10. Fertilization • Fertilization – one sperm fuses with an egg to form a zygote • The zygote now has 2 sets of 23 chromosomes (46 total) • This cell will begin dividing and will ultimately become a child. Zygote

  11. cats • Tell your DOG how we inherit “traits” from our parents

  12. Parents contribute one of each chromosome pair to the child • On a karyotype, there are 2 chromosomes at each site. • These represents the 2 chromosomes received from the parents. One from mom, one from dad. • During meiosis, these will separate into different gametes (sex cells).

  13. Law of segregation • (Pairs) Homologous chromosomes are separated during the formation of gametes

  14. Dogs • Explain the law of segregation to your CAT

  15. Cats • Explain the law of segregation to your DOG

  16. Siblings • Since parents contribute chromosomes randomly, every child inherits a “unique” combination of traits. • Some may resemble mom; some may resemble dad; others will be completely unique • They may be resemble each other or be totally different.

  17. Cats and Dogs • How can we predict the inheritance of traits?

  18. How Can we predict the inheritance of traits? • Punnett Squares use genotypes to predict inheritance • Punnett Squares show the law of segregation in action Mom Dad

  19. Does it matter which side you put the parent’s genotype on? No, the results are the same.

  20. Monohybrid Cross • Monohybrid = a cross between two organisms that predicts the inheritance pattern/probability of only one characteristic/trait

  21. Practice Brown Fur = B • Trait = fur color B = brown fur b = white fur • Which trait is dominant? • Cross a homozygous dominant with a heterozygous dominant • What are the genotypes of the parents? • What percentage of the offspring will have white fur? BB and Bb 0 B b BB Bb B B BB Bb

  22. Check for understanding Two-eyed • A one-eyed purple people eater is crossed with a two-eyed purple people eater. All of their offspring have two eyes. Which trait is dominant? • Use the letter E or e to represent the alleles (variations) for this gene. What is the genotype of the offspring if you cross a purebred one-eyed purple people eater with a homozygous two-eyed purple people eater? • What generation are the offspring of this cross part of? • If you crossed the offspring with each other, how many of the resulting offspring would have two eyes? Ee F 1 1 out of 4 or 25 %

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