Lecture # 6 Date _________ Chapter 14~ Mendel & The Gene Idea

Mendelian genetics 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)

Leading to the Law of Segregation Alternative versions of genes (alleles) account for variations in inherited characteristics For each character, an organism inherits 2 alleles, one from each parent If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance The alleles for each character segregate (separate) during gamete production (meiosis). Mendel’s Law of Segregation

Genetic vocabulary……. Punnett square: predicts the results of a genetic cross between individuals of known genotype Homozygous: pair of identical alleles for a character Heterozygous: two different alleles for a gene Phenotype: an organism’s traits Genotype: an organism’s genetic makeup Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

The Law of Independent Assortment Law of Segregation involves 1 character. What about 2 (or more) characters? Monohybrid cross vs. dihybrid cross The two pairs of alleles segregate independently of each other. Mendel’s Law of Independent Assortment

Non-single gene genetics, I Incomplete dominance: appearance between the phenotypes of the 2 parents. Ex: snapdragons Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: Tay-Sachs disease Multiple alleles: more than 2 possible alleles for a gene. Ex: human blood types

What is the difference between incomplete and codominance? Incomplete-heterozygous phenotype that “appears” to be a blend of both homozygotes. (pink flowers) Codominance-heterozygote that equally expresses the traits from both alleles. (flowers with some red and white)

P Generation Red White CRCR CWCW Gametes CR CW Pink F1 Generation CRCW Fig. 14-10-3 P Generation Red White CRCR CWCW Gametes CR CW Pink F1 Generation CRCW Gametes 1/2 CR 1/2 CW Sperm 1/2 CR 1/2 CW F2 Generation 1/2 CR CRCR CRCW Eggs 1/2 CW CRCW CWCW

Human Blood Types Human blood types come from 3 different alleles. Codominance and multiple alleles Ia, Ib, I Ia and Ib are codominant and produce an antigen (protein) i-no antigen Genotype-Ia,i=A blood type Genotype Ib, i=B blood type Genotype ii=O blood type Book pg 205

Red blood cell appearance Phenotype (blood group) Fig. 14-11 Allele Carbohydrate IA A IB B i none (a) The three alleles for the ABO blood groups and their associated carbohydrates Red blood cell appearance Phenotype (blood group) Genotype IAIA or IA i A IBIB or IB i B IAIB AB ii O (b) Blood group genotypes and phenotypes

Human Blood Types Genotype-Ia,i=A blood type Genotype Ib, i=B blood type Genotype ii=O blood type Genotype Ia,Ib=AB blood type Book pg 205 Donors-

Non-single gene genetics, II Pleiotropy: genes with multiple phenotypic effect. Ex: sickle-cell anemia Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

Pleiotropy Genes have multiple phenotypic effects. Pea plants-the gene that effects flower color also affects the color of the seed coating.

Polygenic Traits Human skin color result of four genes that interact to produce a color range. Eye color-blue, green, brown-still do not know all genes used in eye color.

Epistasis Expression of one gene can interfere with the expression of other genes. Fur color in mammals-2 genes give general color, 2 genes give shading 5th gene-interfers with the expression of other genes (albinism)

Human disorders The family pedigree Recessive disorders: •Cystic fibrosis •Tay-Sachs •Sickle-cell Dominant disorders: •Huntington’s Achondroplasia Testing: •amniocentesis •chorionic villus sampling (CVS)

(b) Is an attached earlobe a dominant or recessive trait? Fig. 14-15c 1st generation (grandparents) Ff Ff ff Ff 2nd generation (parents, aunts, and uncles) FF or Ff ff ff Ff Ff ff 3rd generation (two sisters) ff FF or Ff Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait?

Parents Normal Normal Aa Sperm A a Eggs Aa AA A Normal (carrier) Fig. 14-16 Parents Normal Normal Aa  Aa Sperm A a Eggs Aa AA A Normal (carrier) Normal Figure 14.16 Albinism: a recessive trait Aa aa a Normal (carrier) Albino

Parents Dwarf Normal Sperm Eggs Dwarf Normal Dwarf Normal Dd dd D d Dd Fig. 14-17 Parents Dwarf Normal Dd  dd Sperm D d Eggs Dd dd d Figure 14.17 Achondroplasia: a dominant trait Dwarf Normal Dd dd d Dwarf Normal

Fetal Screening