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Ch. 10- Genetics

Ch. 10- Genetics. Patterns of Inheritance . The Blending Hypothesis of Inheritance. Trait - a variation of a particular character Is the blending hypothesis true??. Gregor Mendel. Austrian Monk Grew pea plants in 1800’s to study patterns of inheritance Genetics - study of heredity.

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Ch. 10- Genetics

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  1. Ch. 10- Genetics Patterns of Inheritance

  2. The Blending Hypothesis of Inheritance • Trait- a variation of a particular character • Is the blending hypothesis true??

  3. Gregor Mendel • Austrian Monk • Grew pea plants in 1800’s to study patterns of inheritance • Genetics- study of heredity

  4. The work of Mendel • Pea plants can self-pollinate and reproduce sexually. • 1st steps- identify “true-breeding” plants • If they self-pollinate, they would produce offspring identical to themselves

  5. The work of Mendel • Pea plants can also cross-pollinate (2 plants as parents) • Studied 7 pea plant traits

  6. Probability • The likelihood that a particular event will occur. • Probability = number of events of choice/ number of possible events • Example:

  7. Probability • Past outcomes don’t influence future ones. • Prob. 1 flip is heads = ½ • Prob. 3 flips is heads= ½ x ½ x ½ = 1/8

  8. Genetics Vocabulary • P generation- “parents”; original pair of plants • F1 generation- 1st offspring • F2- offspring of F1 plants • Hybrid- offspring of 2 different true- breeding parents • Gene- chemical factor that determines traits • Allele- different forms of a gene

  9. More genetics vocab… • For each inherited characteristic, an organism has 2 alleles (1 from each parent) • Homozygous- alleles are the same (AA, aa) • Heterozygous- alleles are different (Aa)

  10. More genetics vocab… • Dominant- when only 1 of the 2 different alleles in a heterozygous individual appears to affect the trait (upper case letter) • Recessive- the other allele that does not appear to affect the trait (lower case letter)

  11. Mendel’s Principle of Dominance • Principle of Dominance- Some alleles are dominant and some are recessive

  12. And more vocab… • Genotype- shows alleles for a trait (Aa) • Phenotype- how a trait is expressed (brown eyes)

  13. Mendel’s Law of Segregation Each parent has two factors (genes) for a particular trait, but only gives one to offspring.

  14. Probability & Punnett Squares • Principles of probability can be used to predict the outcomes of genetic crosses. • Punnett Square- shows all possible outcomes of a genetic cross. • Bill Nye video

  15. Monohybrid Cross • 1 trait is analyzed • Let’s try one! • Steps: • Assign letters to DOMINANT and RECESSIVE alleles • Derive genotypes of parents • Complete punnett square! • Determine probabilities of genotypes and phenotypes.

  16. Example • In pea plants purple flowers are dominant to white flowers. If two white flowered plants are crossed, what percentage of their offspring will be white flowered?

  17. Testcross • To find out if parent with dominant trait is homozygous (YY) or heterozygous (Yy), cross with homozygous recessive mate (yy). • Appearance of the offspring will reveal the genotype of the mystery plant.

  18. Testcross • Short hair is dominant over long hair in guinea pigs. A short haired guinea pig was mated with a long-haired guinea pig. If all of the offspring had long hair, what would the genotype of the short haired guinea pig be?

  19. Incomplete Dominance • For some characteristics, neither allele is dominant. • Heterozygotes have an “intermediate” phenotype

  20. Incomplete Dominance • Purebred Andalusian chickens have either black or white feathers. A hybrid chicken has feathers that appear blue. • Two hybrid chickens produce offspring.

  21. Codominance • Codominance- a heterozygote expresses BOTH traits

  22. Codominance • In cattle, red is dominant and white is dominant. Offspring with a red and white gene are a roan color. • a. A homozygous white cow is crossed with a roan bull.

  23. Multiple Alleles • Many genes have several alleles for each inherited character. • i.e. blood types • A & B are codominant, O is recessive

  24. Multiple Alleles • A heterozygous women with blood type A is married to a man with blood type O. What are the genotypes and phenotypes of the offspring?

  25. The Importance of the Environment • An individual’s phenotype depends on the environment as well as on genes.

  26. Sex-Linked Traits • Females XX • Males XY • Any gene that is located on a sex chromosome (i.e. the “x”) is called a sex-linked gene. • In humans, most sex-linked genes are found on the X chromosome. • ** Y does not carry any genes**

  27. Sex-Linked Traits • In humans, colorblindness is a sex-linked recessive trait. a. A colorblind man has a baby with a hybrid woman.

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