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Mendel’s Principle of Dominance or Recessiveness

Mendel’s Principle of Dominance or Recessiveness. The Father of Genetics. Mendel & The Gene Idea. It All Began with Mendel (FYI). Gregor Mendel was born in 1822. Called the “Father of Genetics” Late 1800 chromosomes and the process of meiosis were unknown.

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Mendel’s Principle of Dominance or Recessiveness

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  1. Mendel’s Principle of Dominance or Recessiveness

  2. The Father of Genetics • Mendel & The Gene Idea

  3. It All Began with Mendel (FYI) • Gregor Mendel was born in 1822. • Called the “Father of Genetics” • Late 1800 chromosomes and the process of meiosis were unknown. • Mendel’s work was considered obscure and unimportant until 1900 • Walter Sutton proposed the Chromosome Theory and people began to listen to his ideas. • Chromosome Theory – specific genes are located on specific chromosomes

  4. 1. Mendel’s Findings • Principle of Dominance and Recessiveness • One allele in a pair may mask the effect of the other • Principle of Segregation • The two alleles for a characteristic separate during the formation of eggs and sperm • Principle of Independent Assortment • The alleles for different characteristics are distributed to reproductive cells independently.

  5. 2. Terminology • Character (heritable feature, i.e., fur color) • Trait (variant for a character, i.e., brown) • True-bred (all offspring of same variety) • Hybridization • (crossing of 2 different true-breds) • P generation (parents) • F1 generation (first filial generation) • F2 generation (second filial generation)

  6. 2. Terminology • Punnett square: • Gene: point on a chromosome that controls the trait • Allele: an alternate form of a gene A or a • Homozygous: identical alleles for a character • Heterozygous: different alleles for a gene • Phenotype: physical traits • Genotype: genetic makeup • Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

  7. What about 2 Traits? • BbLl x BbLl • The Gametes contain one of each of the alleles. (BL). • Each of the offspring contain four alleles exactly like the parents.(BbLl). • Notice the number of possible offspring has increased. • The phenotypic ratio is 9:3:3:1

  8. BbLl x BbLl

  9. Now on your own… Work the Dihybrid Crosses on your own.

  10. Exceptions to Mendel’s Rule Non Mendelian Genetics

  11. Incomplete Dominance • The phenotype of the heterozygote is intermediate between those of the two homozygotes. • Ex) Snap Dragon Color • Red, Pink, White

  12. Co-dominance • Phenotype of both homozygotes are produced in heterozygotes individuals. • Both alleles are expressed equally. • Ex)Roan Cattle White-feathered birds are both homozygotes for both B and W alleles

  13. Multiple Alleles • Ex )Blood type • Blood type A and B are co-dominant, while O is recessive. • Forms possible blood types of A, B, AB, and O.

  14. Blood Also Shows Codominance

  15. Sex-Determination • Chromosome pairs 1-22 are autosomes • Chromosome pair 23 are sex chromosomes • They determine the sex of an individual • XX = female XY = male

  16. Sex-Linked Inheritance • Traits that are only found on the X chromosome • Colorblindness and Hemophilia are examples of sex-linked traits. • These genes are recessive and found only on the X chromosome.

  17. Polygenic Inheritance • Inheritance pattern of a trait that is controlled by two or more genes. • Gene may be on the same chromosome or on different chromosomes. • Ex) Skin color and Height

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