Patterns of Inheritance

1. Patterns of Inheritance Chapter 10

2. Blending Hypothesis of Inheritance • Trait • A variation of a particular characteristic • Blending hypothesis (1800s) • Early explanation of how offspring inherit trait from both parents • Example: if a red flower plant crossed with a yellow flower, the offspring would be orange • Later discarded

3. Gregor Mendel • Austrian monk • Father of Genetics (study of heredity) • Said parents pass on to their offspring separate and distinct genes • Studied 7 characteristics in pea plants

4. True breeding plants • A true plant will show the same physical appearance generation after generation after self-fertilization • Cross fertilization • The sperm from the pollen of one true flower fertilizes the eggs in the flower of a different plant

5. Mendel's Experiments • Cross-fertilized 2 true-breeding plants each with contrasting traits (i.e. white and purple flowers) • What color of flowers do you think the offspring plants were?

6. Principle of Segregation • P generation • Parental plants (purebred and true breeding) • F1 generation ( F for filial “son”) • Hybrid offspring • Hybrids • The offspring of 2 different true-breeding varieties • F2 generation • When F1 self-fertilize or fertilize each other

7. Monohybrid Cross • Monohybrid cross • Cross fertilization in which only one physical characteristic is considered • In Mendel's cross, all F1 were purple but ¼ of F2 were white

8. Gene Hypotheses #1 • There are alternative forms of genes which determine physical appearances • Allele is the term • Example: Flower color can be white or purple

9. Gene Hypotheses #2 • For each characteristic, an organism has 2 alleles for genes controlling the physical appearances (one from each parent) • If 2 alleles are the same= homozygous • If 2 alleles are different =heterozygous

10. Gene Hypotheses #3 • Dominant alleles determine the physical appearance in a heterozygous individual. • Recessive allele is the other allele that does not affect the physical appearance • Capital letter represents dominant allele: P • Lower case letter represents recessive allele: p

11. Phenotype is the physical appearance • purple • purple • white • Genotype is the genetic makeup • Possible genotype are PP, Pp, pp.

12. Gene Hypotheses #4 • The two alleles for a character segregate (separate) during meiosis so that each gamete carries only one allele for each character, known as principle of segregation.

14. Punnett Square • The alignment of combination of gametes to form zygotes with pairs of alleles is random • Like tossing a coin. • Punnett Square is a diagram that shows all possible outcomes of a genetic cross. • Used to predict probabilities of outcomes if you know the genotypes of the parents

15. The Testcross • Breeds an individual of unknown genotype, but dominant phenotype (purple) with a homozygous recessive individual (white) • Appearance of F1 will reveal the genotype of the mystery parent • If white flowers are produced, the unknown parent must be heterozygous (Pp) and have a recessive trait

16. Intermediate Dominance • Heterozygotes have a phenotype intermediate between the phenotypes of the two homozygote • This is referred to as INCOMPLETE DOMINANCE • Rules: (example: snapdragon flowers) • Capital/lower case letters not used • Instead, a C for “color” is paired with a superscript R for “red” and W for “white” • CR CRis red and CW CW is white • CR CW is pink

18. There is a breed of chicken called Andalusians, black and white parents produce F1 hybrid offspring, called "blues," with grayish-blue feathers. Because neither the black nor white allele is dominant, capital and lowercase letters are not used to represent them.

19. Instead, a C for "color" is paired with a superscript B for "black" or W for "white" to represent the two alleles. A heterozygote chicken has one of each allele, CBCW, and is grayish-blue in color

20. Although the F1 phenotypes are intermediate, this inheritance pattern does not support the blending hypothesis. This is because the parent phenotypes can reappear in the F2 generation.

21. Multiple alleles • Heterozygote express the distinct traits of both alleles • Example: Human blood system • A, B, AB, or o • The letters are antigens found on the surface of red blood cells • Red blood cells may be coated with one protein (A), the other (B), both (AB), or neither (O) • There are six possible genotype combinations

22. ABO blood type is a genetic example of multiple alleles. There are three alleles in the gene pool for ABO blood type. IA IB i

23. IA codes for protein A IB codes for protein B i codes for neither protein A nor protein B.

24. Within this multiple allele pool the gene interactions illustrate both simple dominance as well as co-dominance. Remember each individual has only two alleles for each trait even if there are multiple alleles in the gene pool. IAIA both code for A type blood IAi

26. ABO Blood System • Antibodies (proteins) also found in the blood serum that attacks foreign antigens • Blood A has antibody Anti-B • Blood B has antibody Anti-A • Blood AB has no antibody • Blood O has Antibody Anti A and B • Blood O is the universal donor • Blood AB can receive any blood type

27. Rh Factor • Rh positive (Rh +) has protein in blood • Rh negative (Rh -) has no protein in blood • Rh+ is dominant

28. Blood Typing

30. Sex-linked genes • The eggs contain a single X chromosome and sperm contain either an X or a Y • Sex of the offspring depends on whether the sperm that fertilizes the egg has an X or a Y • Any gene located on a sex chromosome (X) is called a sex-linked gene • Most are found on the X (2,000) and few on the Y (24)

31. Sex-linked traits • Written as a XRXr for heterozygous. • Y chromosome carries no allele and the phenotype is dependant upon the woman’s allele • Therefore, males carry one allele for a sex-linked trait.

32. Sex-linked disorders • Red-green blindness • Hemophilia (inability of blood to clot)