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Patterns of Inheritance

Patterns of Inheritance. Heredity – the passing of traits from parent to offspring Genetics - the study of inheritance Trait – variation of a character (eye color, hair color, etc.). Gregor Mendel. First biologist to experiment with inheritance .

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Patterns of Inheritance

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  1. Patterns of Inheritance • Heredity – the passing of traits from parent to offspring • Genetics - the study of inheritance • Trait – variation of a character (eye color, hair color, etc.)

  2. Gregor Mendel • First biologist to experiment with inheritance. • Hypothesized that parents pass on to their offspring separate and distinct genes responsible for inherited traits. • Said genes retain their own identities. • Worked with pea plants. • Why?

  3. Types of pollination • Self-pollination – sperm from flower fertilizes egg from same flower. • Cross-pollination – sperm from one flower crosses with egg from a different flower. (Mendel used)

  4. Terms • Gene – part of a chromosome that determines a trait • Allele – alternate form of a gene • One allele from mother, one from father

  5. Mendel found… • P – parent • F1 – offspring • F2 – offspring of offspring Types of alleles: dominant and recessive Dominant – allele that affects the trait (capital letter) Recessive – does not affect the trait (lower-case letter) Generally, dominant will show over recessive alleles.

  6. Alleles • There are 2 alleles per gene. • Ex/ T (tall, dominant) and t (short, recessive) • Combinations: • TT • Tt • tt

  7. Principle of Segregation • Two alleles for a character segregate (separate) during formation of gametes. • Each gamete carries only one allele for each character. • Alleles are paired during fertilization again.

  8. Punnett Square • Calculates probabilities of outcomes from a genetic cross. • Ex/ Height: Tall is dominant over short. • Use “t” for height • TT x tt

  9. Punnett Square Example T T t t

  10. Homozygous - Purebred = Pure breeding = True breeding • Has two identical alleles - RR or rr • Homozygous Dominant: RR • Homozygous Recessive: rr Heterozygous - Hybrid • Has two different alleles - Rr

  11. Genotype - the alleles that make up the gene (eg. BB) • Phenotype - the physical expression of the gene (eg. Black hair)

  12. Dihybrid Cross • A cross between two organisms where two different genes are studied • The genes are located on separate chromosomes, so the traits are unrelated

  13. Dihybrid example • Brown eyes are dominant over blue. Dimples are dominant over no dimples. • BbDd x BbDd BD Bd bD bd BD BBDD BBDd BbDD BbDd Bd BBDd BBdd BbDd Bbdd bD BbDD BbDd bbDD bbDd bd BbDd Bbdd bbDd bbdd

  14. Dihybrid Example BD Bd BD Bd • BBDd x bbDD bD BbDD BbDd BbDD BbDd bD BbDD BbDd BbDD BbDd bD BbDD BbDd BbDD BbDd bD BbDD BbDd BbDD BbDd

  15. Ways to Write answers • FractionPercentRatio • ½ , ½ 50%, 50% 1:1 • 4/4 (all) 100% 1 • ¾, ¼ 75%, 25% 3:1

  16. Incomplete Dominance • There is no dominant or recessive, the heterozygous condition results in a "blending" of the two traits. • In snapdragons, red flowers are incompletely dominant over white flowers. • RR- red • Rr- pink • rr- white • Ex/ • In rodents, black fur is incompletely dominant over white fur. • BB-black • Bb- gray • bb- white • What would be the phenotype fraction of the F1 if two gray mice mated?

  17. Codominance • Both alleles can be equally expressed • Most common example blood types • There are four blood types (phenotypes): A, B, AB, and O • Blood type is controlled by three alleles: A, B, O • A and B are both dominant • O is recessive

  18. Blood typing continued • Antigens are on the surface of Red Blood Cells • Will cause a reaction if your immune system does not recognize them as being part of you

  19. Blood Typing practice problem • Example: • A woman with AB blood is crossed with a man with heterozyous A blood. What would be the phenotypic percent of the F1 generation? • AB x AO A B A O

  20. Blood transfusions and Rh Factor • Rh = rhesus monkey • Has Rh antigens = Rh+ • No Rh antigens = Rh- • Rh+ can only donate to other Rh+ • Rh- can donate to both Rh+ and Rh-

  21. Who Can Receive What Type? Patients with Type:Can receive type: O+ O+, O- A+ O+, A+, O-, A- B+ O+, B+, O-, B- AB+ O+, A+, B+, AB+, O-, A-, B-, AB- O- O+, A+, B+, AB+, O-, A-, B-, AB- A- O-, A- B- O-, B- AB- O-, A-, B-, AB-

  22. Who can Donate to Who? Type:Can be given to patients with type: O+ O+, A+, B+, AB+ A+ A+, AB+ B+ B+, AB+ AB+ AB+ O- O+, A+, B+, AB+, O-, A-, B-, AB- A- A+, AB+, A-, AB- B- B+, AB+, B-, AB- AB- AB+, AB-

  23. Sex-Linked • Traits that are linked to the X chromosome • Humans have 44 autosomes and 2 sex chromosomes • Male: XY Female: XX • X chromosome carries more genes

  24. Sex-Linked Example • In fruit flies, the allele for eye color is sex-linked • Red eyes are dominant to white eyes What are the different allele combinations? Female red Male red Female white Male white Can males be heterozygous or carriers for a sex-linked trait?

  25. Sex-linked practice • A female fly with heterozygous red eyes is crossed with a male fly with white eyes? What are the phenotypic fractions of the F1 generation?

  26. Polygenic Inheritance • Traits that determined by the combined effect of more than one pair of genes

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