Genetics

Gregor Mendel

Genetic Concepts Phenotype –Physical characteristics of organism –Result of gene expression –Biochemical function of proteins determine physical characteristics of organism Genotype –Set of alleles present in genome of organism –Alleles are versions of genes

Segregating Traits in Sweet Pea

Genetic Crosses Monohybrid –cross between two variants of a single trait –ABO type A x ABO type B Dihybrid –cross between two variants of two traits –ABO type A, Rh+ x ABO type B, Rh-

Mendel’s Monohybrid Crosses GY Pea Color Trait x All Yellow P Generation F1F1 x F2F2 ¾ of progeny yellow ¼ of progeny green

What Does It Mean, Mendel??? The disappearance of the green trait in F 1 means it is recessive The appearance of only the yellow trait in F 1 means it is dominant A recessive trait is seen if only 2 recessive alleles of that gene are present The dominant trait is seen if 1 or 2 alleles of that gene are present THERE MUST BE TWO ALLELES OF EACH GENE THE ALLELES SEPARATE DURING REPRODUCTION

Mendel’s Dyhybrid Crosses Y Pea Color Trait & Height Trait x All Yellow & Tall P Generation F1F1 G x

Mendel’s Dihybrid Cross 9/16 yellow & tall 3/16 green & tall 3/16 yellow & short 1/16 green & short F2F2

What Does It Mean, Mendel??? Yellow and Tall are dominant traits; green & short are recessive EITHER ALLELE CONTROLLING COLOR CAN ASSORT WITH EITHER ALLELE CONTROLLING HEIGHT

Mendel’s Principles Law of Segregation –There are two alleles (distinct copies) of every gene in the genome of an organism –The two alleles of each gene are separated during meiosis and put into separate gametes so that each gamete has only one allele of every gene. Law of Independent Assortment –Any allele of one gene may assort with any allele of any other, unlinked gene –All possible allelic combinations are possible if enough gametes are produced

Karyotype Y

Chromosomes

DNA

Chromosomes & Genes Homologous Chromosomes Sister Chromatids Non-Sister Chromatids Loci Alleles Maternal Homolog Paternal Homolog

Genetic Concepts Genotype –Homozygous Same alleles at loci on each homolog –ZZ –Heterozygous Different alleles at loci on each homolog –Yy Homologous Chromosomes Sister Chromatids Non-Sister Chromatids Loci Alleles Maternal Homolog Paternal Homolog Z

Meiosis I

Crossing Over (Not with John Edward) Y Z y z

Meiosis II

Meiosis Meiosis Movie on YouTube

Inheritance Patterns Complete (simple) Dominance Co-dominance Intermediate Dominance

Complete Dominance/Recessiveness Phenotype: ABO type A Genotype: I A I A, I A O Phenotype: ABO type B Genotype: I B I B, I B O Phenotype: ABO type O Genotype: OO

Co-Dominance Phenotype: ABO type AB Genotype: I A I B Both A & B alleles encode functional enzymes Both enzymes work at same time Both modifications are made simultaneously Phenotype is combined effect of both A & B enzymes

Intermediate Dominance dosage effect B better than B’ BB > BB’ > B’B’

Intermediate Dominance Crop-eared trait in Scottish Cruachan Highland Cattle CC – cropped, Cc – smaller than normal, cc – normal size

Incomplete Dominance rr Rr RR

Linkage Genes on same chromosome are separated by crossing over during meiosis I Genes located near each other, on the same chromosome, infrequently separate –They are “linked” Linked genes are often inherited together

Chromosomal Sex Determination In most organisms, males & females have a unique pair of chromosomes which determine sex XY mechanism –Males – XY; females - XX ZW mechanism –Males – ZZ; females - ZW X0 mechanism –Males – X_ ; females – XX Haploid/Diploid mechanism –Males – haploid; females - diploid

Sex Linkage Genes on the X or Y chromosomes are sex-linked A phenotype caused by a gene on the X chromosome will appear in males more frequently Normal

Non-Chromosomal Sex Determination No chromosomal differences between sexes Environmental Determinants –temperature reptiles Physiological Determinants –pheromones marine invertebrates –hormones some fish