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Genetics

Explore the basics of genetics, including the laws of inheritance discovered by Gregor Mendel, genetic vocabulary, and the concepts of genotype and phenotype. Learn about hybridization and the role of probability in genetics, as well as the determination of sex and the inheritance of sex-linked traits. Discover the fascinating world of genetics and how traits are passed from generation to generation.

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Genetics

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  1. Genetics

  2. Genetics: the study of heredity

  3. Heredity: the passing on of characteristics from the parent to the offspring

  4. Background (not in notes) • Gregor Mendel: first lab in the garden • Studied garden peas • Performed cross-breeding with different types of pea plants - yellow peas x green peas - wrinkled peas x non wrinkled plants • Determined that the inheritance of traits followed laws and that determined the ratios of how often those traits would be seen in the offspring of subsequent generations

  5. For Example Gregor Mendel crossed pea plants: Green X Yellow Green (100%) Then he crossed the offspring Green (75%) Yellow (25%) HMMM… Interesting

  6. So before we go any further:Important Genetics Vocab!!!! • Genes – a segment of a chromosome which codes for something specific • Ex: seed colour

  7. Alleles: different forms of a gene (variations) • Each cell will have two allele • Remember that each cell has homologous chromosomes • Eg: The gene is for seed colour but the alleles are for yellow and green

  8. Dominant: an allele that shows over the other allele of the gene. • The dominant allele is written in uppercase. • Green colour is dominant = G • If present, it always shows! (it wins!) • Recessive: an allele that does not up over the dominant allele. • It only shows up when the other allele is recessive • Yellow colour is recessive = g • Need to have 2 recessives together for this to show! (otherwise it hides)

  9. Green X Yellow (GG) Dominant (gg) Recessive Green (100%) (Gg)

  10. Homozygous – an individual with copies of the same type of allele • Eg: GG (green peas) x gg (yellow peas) • Two copies of green Two copies of yellow • Heterozygous – an individual with copies of two DIFFERENT alleles • Eg: Gg – (green peas) • One copy of the dominant green seed allele and one copy of the recessive allele (yellow) • Dominant allele wins… therefore the peas show as green even though they have a the yellow recessive allele

  11. Genotype: The particular combination of alleles an organism has • Eg: GG or Gg or gg • Phenotype: The physical appearance of the organism. • Green seed colour is the phenotype (GG or Gg genotype) • Yellow seed colour (gg is the genotype)

  12. Hybrid – crossing of the two forms of a trait. • Pure bred- an individual with only one type of allele • F1 offspring (F1 generation) – the offspring of two pure bred individuals • F2 offspring (F2 generation)- the offspring of the F1 individuals bred with each other

  13. For Example Pure bred individuals Gregor Mendel crossed pea plants: Green X Yellow Green (100%) Then he crossed the offspring Green (75%) Yellow (25%) HMMM… Interesting F1 Offspring F2 Offspring

  14. Genetics and Probability • Probability is the chance or likelihood of something occuring • Does not tell you what it will be but what is possible • Ex. 50% chance a baby is a boy or girl • Ex. Chance of tossing two heads in a roll is: ½ x ½ = ¼

  15. So: • During meiosis different alleles can go into different cells

  16. A plant that is heterozygous for the seed colour Gg can give a G allele or a g allele • A Punnett square is one way to show all the possible genotypes of offspring ANIMATION

  17. Cross between 2 pure breds (homozygous) Genotype results: Gg Phenotype results: 100% Green peas Cross between 2 individuals from F1 generation (heterozygous) Genotype results: GG, Gg, gg Phenotype results: 75% Green peas 25% Yellow peas

  18. Sex Determination in Humans • Humans have 22 numbered chromosomes and a 23rd pair that is labeled XX or XY • A pair of XX produces a female • A pair of XY produces a male • The male parent determines the sex of the offspring

  19. Sex Linked Genes • Some genes are located only on the X or Y chromosome • Eg: colourblindness is a recessive gene found on the X chromosome • A male with the recessive X gene will have colourblindness • A female with the recessive X gene may have another copy that is dominant and therefore is only a carrier for colourblindness

  20. Sex linked traits are usually exhibited by males rather than females because males have only one copy of the X chromosome (XX vs. XY) • If the X chromosome carries the recessive allele, only the male will be affected • Females are often carriers because the second copy of the X chromosome is dominant and the recessive trait is oppressed.

  21. Hemophelia • A body’s inability to clot blood properly

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