Introduction to Genetics Glencoe Chapters 10-11

Mendelian Genetics

Mendelian Genetics Allele-an alternate form of a single gene passed on from generation to generation Reside at the same locus on homologous chromosomes One inherited from each parent If two alleles differ, the one that determines the organism’s appearance is the dominant allele The other allele is recessive and has no effect on the organism’s appearance. Genotype: PP aa Bb Heterozygous P a b B Gene loci Recessive allele Dominant allele Homozygous for the dominant allele Homozygous for the recessive allele

Mendelian Genetics Homozygous-having two of the same alleles for a particular trait AA or aa Heterozygous-having two different alleles for a particular trait Aa

Mendelian Genetics Genotype: an organism’s allele pairs Phenotype: observable characteristic or outward expression of an allele pair

Mendelian Genetics Law of segregation-two alleles for each trait separate during meiosis Law of independent assortment-random distribution of alleles occurs during gamete formation

Mendelian Genetics Monohybrid cross-involves hybrids for a single trait Dihybrid cross-involves hybrids for two traits

Punnett Squares Monohybrid cross

Punnett Squares Dihybrid cross-four types of alleles from female gamete and four types of alleles from male gamete The result is a 9:3:3:1 ratio

Punnett Squares The rule of multiplication F1 genotypes Bb female Formation of eggs F2 genotypes Bb male Formation of sperm B b 1 2 4 The rule of multiplication Calculates the probability of two independent events The rule of addition Calculates the probability of an event that can occur in alternate ways

Gene Linkage and Polyploidy Genetic recombination-new combination of genes produced by crossing over and independent assortment Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs.

Gene Linkage and Polyploidy Genes that are located close together on the same chromosome are linked and usually travel together during gamete formation Linked genes can separate during crossing over Chromosome map-drawing showing sequence of genes on a chromosome

Gene linkage and Polyploidy Polyploidy-occurrence of one or more extra sets of all chromosomes in an organism Triploid organism 3n Many flowering plants are polyploid

Basic Patterns of Human Inheritance Parents Offspring Sperm Normal Dd  D d Eggs D d DD (carrier) dd Deaf Recessive Genetic Disorders Disorder that occurs when an organism is homozygous recessive Carrier-an individual who is heterozygous for a recessive disorder Cystic fibrosis, albinism, Tay-Sachs disease

Basic Patterns of Human Inheritance Dominant Genetic Disorders Huntington’s disease Achondroplasia

Basic Patterns of Human Inheritance Dd Joshua Lambert Abigail Linnell D ? John Eddy Hepzibah Daggett dd Jonathan Elizabeth Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing Pedigree-diagram that traces the inheritance of a particular trait through several generations

Basic Patterns of Human Inheritance Solving Pedigrees

Complex Patterns of Inheritance P generation F1 generation F2 generation Red RR Gametes  White rr Sperm Eggs Pink Rr R r rR 1 2 Incomplete Dominance- heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes

Complex Patterns of Inheritance Codominance-both alleles are expressed in the heterozygous condition Sickle cell disease-affects ability to carry oxygen heterozygous individuals have both sickle shaped and normal shaped cells High levels of sickle cell in Africa where malaria is prevalent because those who are heterozygous have higher resistance to malaria

Complex Patterns of Inheritance Multiple alleles-inheritance involving more than two forms of an allele Blood groups in humans- alleles A and B are codominant O-universal donor AB-universal recipient

Complex Patterns of Inheritance Epistasis-one allele hides the affect of another allele

Complex Patterns of Inheritance Sex determination-XX or XY X chromosome carries variety of genetics necessary for development of males and females Y chromosome mainly has genes related to male development X-inactivation-one of the X chromosomes in a female cell is inactivated Completely random in each cell Barr bodies-inactivated X chromosomes

Complex Patterns of Inheritance Sex-linked traits-traits controlled by genes on X chromosome Since males only have one X chromosome, they are affected by recessive X-linked traits more than females Red-green color blindness Hemophilia

Complex Patterns of Inheritance P generation F1 generation F2 generation Sperm Eggs aabbcc (very light) AABBCC (very dark) AaBbCc  1 8 64 6 15 20 Skin color Fraction of population Polygenic traits- phenotypic traits that arise from interaction of multiple pairs of genes

Complex Patterns of Inheritance Environmental influences on phenotype Sunlight and water Temperature