MENDELIAN GENETICS

Genetics is everywhere these days – and it will continue as a dominant force in biology and society for decades to come.

Gregory Mendel – Australian monk Afterwards became Father of modern genetics Researched with pea plants Developed ideas of dominance and trait segregation

How Genetics Began  The passing of traits to the next generation is called inheritance, or heredity.  Mendel performed cross-pollination in pea plants.  Mendel followed various traits in the pea plants he bred. MENDELIAN GENETICS

 Mendel studied seven different traits.  Seed or pea color  Flower color  Seed pod color  Seed shape or texture  Seed pod shape  Stem length  Flower position MENDELIAN GENETICS

 The second filial (F 2 ) generation is the offspring from the F 1 cross. MENDELIAN GENETICS  Mendel crossed a pure yellow pea with a pure green pea  The offspring of this P cross are called the first filial (F 1 ) generation.

Genes in Pairs  Allele  An alternative form of a single gene passed from generation to generation  They can be Dominant or  Recessive MENDELIAN GENETICS

Dominance  An organism with two of the same alleles for a particular trait is homozygous.  An organism with two different alleles for a particular trait is heterozygous. MENDELIAN GENETICS

Genotype and Phenotype  An organism’s allele pairs are called its genotype.  The observable characteristic or outward expression of an allele pair is called the phenotype.  An example of Genotype is Yy  An example of Phenotype is yellow MENDELIAN GENETICS

Mendel’s Law of Segregation  Two alleles for each trait separate during meiosis.  During fertilization, two alleles for that trait unite.  Heterozygous organisms are called hybrids. MENDELIAN GENETICS

Law of Independent Assortment  Random distribution of alleles occurs during gamete formation  Genes on separate chromosomes sort independently during meiosis.  Each allele combination is equally likely to occur. MENDELIAN GENETICS

Genetic Recombination  The new combination of genes produced by crossing over and independent assortment MENDELIAN GENETICS  Combinations of genes due to independent assortment can be calculated using the formula 2 n, where n is the number of chromosome pairs.

Monohybrid Cross  A cross that involves hybrids for a single trait is called a monohybrid cross. MENDELIAN GENETICS

Dihybrid Cross  The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.  Dihybrids are heterozygous for both traits. MENDELIAN GENETICS

Probability The likelihood that a particular event will occur Example: What is the probability that a coin when flipped will be heads?.. ½ X ½ = 50% What is the probability that a coin when flipped will be heads three times in a row? ½ X ½ X ½ = 1/8 or 1 out of 8 chance MENDELIAN GENETICS

Punnett Squares  Predict the possible offspring of a cross between two known genotypes  Shows probability

Punnett Square— Dihybrid Cross  Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.  The resulting phenotypic ratio is 9:3:3:1.

Gene Linkage  The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.

Polyploidy  Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.  A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes.

Complex Patterns of Inheritance Incomplete Dominance  The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.

Codominance  Both alleles are expressed in the heterozygous condition. Complex Patterns of Inheritance

Polygenic Traits  Polygenic traits arise from the interaction of multiple pairs of genes. Complex Patterns of Inheritance

Multiple Alleles  Blood groups in humans  ABO blood groups have three forms of alleles. Complex Patterns of Inheritance

Coat Color of Rabbits  Multiple alleles can demonstrate a hierarchy of dominance.  In rabbits, four alleles code for coat color: C, c ch, c h, and c. Complex Patterns of Inheritance

Coat Color of Rabbits Light gray Dark gray Himalayan Albino Chinchilla Complex Patterns of Inheritance

Dosage Compensation  The X chromosome carries a variety of genes that are necessary for the development of both females and males.  The Y chromosome mainly has genes that relate to the development of male characteristics. Complex Patterns of Inheritance

Sex Determination  Sex chromosomes determine an individual’s gender. Complex Patterns of Inheritance

Sex-Linked Traits  Genes located on the X chromosome  Red-green color blindness  Hemophilia Complex Patterns of Inheritance Sex-Linked Traits

Environmental Influences  Environmental factors  Diet and exercise  Sunlight and water  Temperature Complex Patterns of Inheritance

Pedigrees  A diagram that traces the inheritance of a particular trait through several generations

 Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size. Karyotype Studies  Images of chromosomes stained during metaphase  Chromosomes are arranged in decreasing size to produce a micrograph.

Cystic Fibrosis  Affects the mucus-producing glands, digestive enzymes, and sweat glands  Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.  Without sufficient chloride ions in the cells, a thick mucus is secreted. Basic Patterns of Human Inheritance

Recessive Genetic Disorders  A recessive trait is expressed when the individual is homozygous recessive for the trait.

Albinism  Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes  White hair  Very pale skin  Pink pupils Basic Patterns of Human Inheritance

Tay-Sachs Disease  Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides  Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration. Basic Patterns of Human Inheritance

Dominant Genetic Disorders  Huntington’s disease affects the nervous system.  Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short. Basic Patterns of Human Inheritance

Sickle-cell Disease  Changes in hemoglobin cause red blood cells to change to a sickle shape.  People who are heterozygous for the trait have both normal and sickle-shaped cells. Sickle cell Normal red blood cell 7766x Basic Patterns of Human Inheritance

1.A 2.B 3.C 4.D CDQ 1 A. # B. x C. r D. n Which symbol is used to represent the number of chromosomes in a gamete? Chapter Diagnostic Questions

1.A 2.B 3.C 4.D CDQ 2 Chapter Diagnostic Questions A. Felix Mendelssohn B. Gregor Mendel C. Dr. Reginald Punnett D. Albert Einstein Name the person known as the father of genetics.

1.A 2.B 3.C 4.D CDQ 3 Chapter Diagnostic Questions A. gamete B. hybrid C. phenotype D. genotype Which term refers to the outward expression of an allele pair?

1.A 2.B 3.C 4.D FQ 1 Segments of DNA that control the production of proteins are called _______. A. chromatids B. chromosomes C. genes D. traits Formative Questions

1.A 2.B 3.C 4.D FQ 2 Formative Questions What is the term for a pair of chromosomes that have the same length, same centromere position, and carry genes that control the same traits? A. diploid B. heterozygous C. homozygous D. homologous

1.A 2.B 3.C 4.D FQ 3 Formative Questions How does the number of chromosomes in gametes compare with the number of chromosomes in body cells? A. Gametes have 1/4 the number of chromosomes. B. Gametes have 1/2 the number of chromosomes. C. Gametes have the same number of chromosomes. D. Gametes have twice as many chromosomes.

1.A 2.B 3.C 4.D FQ 4 Formative Questions What type of organisms only reproduce asexually? A. bacteria B. protists C. plants D. simple animals

1.A 2.B 3.C 4.D FQ 5 What is the name for different forms of a single gene that are passed from generation to generation? A. alleles B. genotypes C. phenotypes D. traits Formative Questions

1.A 2.B 3.C 4.D FQ 6 Formative Questions Which pair of alleles is heterozygous? A. RR B. Rr C. rr D. yR

1.A 2.B 3.C 4.D FQ 7 Formative Questions In rabbits, gray fur (G) is dominant to black fur (g). If a heterozygous male is crossed with a heterozygous female, what is the phenotypic ratio of the possible offspring? A. 1:1 B. 1:2:1 C. 2:1 D. 3:1

1.A 2.B 3.C 4.D FQ 10 Formative Questions What is the term for an organism that has one or more sets of extra chromosomes in its cells? A. diploid B. gamete C. hybrid D. polyploid

1.A 2.B 3.C 4.D Standardized Test Practice STP 4 To which step in this process does the law of segregation apply? A. grows into plant B. gamete formation C. fertilization D. seed development