Patterns of Inheritance Chapter 10 Blending Hypothesis of

Patterns of Inheritance Chapter 10

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

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

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

Mendel's Experiments n n 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?

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

Monohybrid Cross n Monohybrid cross n Cross fertilization in which only one physical characteristic is considered n In Mendel's cross, all F 1 were purple but ¼ of F 2 were white

• There alternative forms of genes which determine physical appearances n n Allele is the term Example: Flower color can be white or purple

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

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

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

n 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.

Dihybrid Cross: a cross that shows the possible offspring for two traits Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

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

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 no 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, CBCW, and is grayishblue 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 n n Heterozygote express the distinct traits of both alleles Example: Human blood system n A, B, AB, or o n The letters are antigens found on the surface of red blood cells n Red blood cells may be coated with one protein (A), the other (B), both (AB), or neither (O) n 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. IA IB i

IA codes for protein A IB 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. IA IA both code for A type blood IA i

Phenotype Genotype Protein on RBC (antigen) Antibodies in the blood plasma Type A IA IA and IA i A b Type B IB IB and IB i B a Type AB IA I B A and B ------- Type O ii ------ a and b

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

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

Some of us have it, some of us don't. If it is present, the blood is Rh positive, if not it's Rh negative. So, for example, some people in group A will have it, and will therefore be classed as A+ (or A positive). While the ones that don't, are A- (or A negative). And so it goes for groups B, AB and O. 85% of the population is Rh positive, the other 15% of the population is running around with Rh negative blood.

Do you know which blood group you belong to? According to above blood grouping systems, you can belong to either of following 8 blood groups:

• A person with Rh- blood can develop Rh antibodies in the blood plasma if he or she receives blood from a person with Rh+ blood, whose Rh antigens can trigger the production of Rh antibodies. • A person with Rh+ blood can receive blood from a person with Rh- blood without any problems.

Definition n Some traits are determined by the combined effect of two or more pairs of alleles. These traits are called polygenic traits. Each pair of alleles adds something to the resulting phenotype. Other names for polygenic traits are multifactorial traits, or quantitative traits.

Polygenic traits are continuous n n Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur! For example, height is a polygenic trait.

Polygenic Traits are Continuos n When dealing with polygenic traits that are only controlled by two pairs of alleles, we can complete Punnett squares to determine the genotypes and phenotypes of the F 1 generation.

Blood Typing Blood Type Anti-a Sera Anti-b Sera A Clumping No clumping B No clumping Clumping AB Clumping O No clumping

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

Sex-linked traits n n n 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 sexlinked trait.

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