Patterns of Inheritance Chapter 10

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

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

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

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

Principle of Segregation P generation P generation Parental plants (purebred and true breeding) Parental plants (purebred and true breeding) F 1 generation ( F for filial “son”) F 1 generation ( F for filial “son”) Hybrid offspring Hybrid offspring Hybrids Hybrids The offspring of 2 different true-breeding varieties The offspring of 2 different true-breeding varieties F 2 generation F 2 generation When F1 self-fertilize or fertilize each other When F1 self-fertilize or fertilize each other

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

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

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

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

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

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. 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.

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

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

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

There is a breed of chicken called Andalusians, black and white parents produce F 1 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.

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, C B C W, and is grayish- blue in color

Although the F 1 phenotypes are intermediate, this inheritance pattern does not support the blending hypothesis. This is because the parent phenotypes can reappear in the F 2 generation.

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

ABO blood type is a genetic example of multiple alleles. There are three alleles in the gene pool for ABO blood type. I A I B i

I A codes for protein A I B codes for protein B i codes for neither protein A nor protein B.

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. I A both code for A type blood I A i

PhenotypeGenotype Protein on RBC (antigen) Antibodies in the blood plasma Type A I A I A and I A i Ab Type B I B I B and I B i Ba Type AB IA IBIA IBIA IBIA IB A and B Type O ii a and b

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

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

Blood Typing Blood Type Anti-a Sera Anti-b Sera AClumping No clumping B Clumping ABClumpingClumping O

Sex-linked genes The eggs contain a single X chromosome and sperm contain either an X or a Y 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 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 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) Most are found on the X (2,000) and few on the Y (24)

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

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