© 2013 Pearson Education, Inc. Lectures by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece Chapter 9 Patterns of Inheritance

People have selected and mated dogs with preferred traits for more than 15,000 years. Over thousands of years, such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today. The biological principles underlying genetics have only recently been understood. Biology and Society: Our Longest-Running Genetic Experiment: Dogs © 2013 Pearson Education, Inc.

Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel –worked in the 1860s, –was the first person to analyze patterns of inheritance, and –deduced the fundamental principles of genetics. HERITABLE VARIATION AND PATTERNS OF INHERITANCE © 2013 Pearson Education, Inc.

In an Abbey Garden Mendel studied garden peas because they –were easy to grow, –came in many readily distinguishable varieties, –are easily manipulated, and –can self-fertilize. © 2013 Pearson Education, Inc.

A character is a heritable feature that varies among individuals. A trait is a variant of a character. Each of the characters Mendel studied occurred in two distinct traits. In an Abbey Garden © 2013 Pearson Education, Inc.

Mendel –created purebred varieties of plants and –crossed two different purebred varieties. In an Abbey Garden © 2013 Pearson Education, Inc.

Hybrids are the offspring of two different purebred varieties. –The parental plants are the P generation. –Their hybrid offspring are the F 1 generation. –A cross of the F 1 plants forms the F 2 generation. In an Abbey Garden © 2013 Pearson Education, Inc.

Mendel’s Law of Segregation Mendel performed many experiments. He tracked the inheritance of characters that occur as two alternative traits. © 2013 Pearson Education, Inc.

Figure 9.4 White Purple Recessive Dominant Green Yellow Terminal Axial Wrinkled Round Green Yellow Seed shape Seed color Flower position Flower color Pod color Recessive Dominant Pod shape Stem length Inflated Constricted Tall Dwarf

Monohybrid Crosses A monohybrid cross is a cross between purebred parent plants that differ in only one character. © 2013 Pearson Education, Inc.

Figure Purple flowers F 1 Generation White flowers P Generation (purebred parents) All plants have purple flowers F 2 Generation Fertilization among F 1 plants (F 1  F 1 ) of plants have purple flowers of plants have white flowers

Mendel developed four hypotheses from the monohybrid cross, listed here using modern terminology (including “gene” instead of “heritable factor”). 1. The alternative versions of genes are called alleles. Monohybrid Crosses © 2013 Pearson Education, Inc.

2. For each inherited character, an organism inherits two alleles, one from each parent. –An organism is homozygous for that gene if both alleles are identical. –An organism is heterozygous for that gene if the alleles are different. Monohybrid Crosses © 2013 Pearson Education, Inc.

3. If two alleles of an inherited pair differ, –then one determines the organism’s appearance and is called the dominant allele and –the other has no noticeable effect on the organism’s appearance and is called the recessive allele. Monohybrid Crosses © 2013 Pearson Education, Inc.

4. Gametes carry only one allele for each inherited character. –The two alleles for a character segregate (separate) from each other during the production of gametes. –This statement is called the law of segregation. Monohybrid Crosses © 2013 Pearson Education, Inc.

Do Mendel’s hypotheses account for the 3:1 ratio he observed in the F 2 generation? A Punnett square highlights –the four possible combinations of gametes and –the four possible offspring in the F 2 generation. Monohybrid Crosses © 2013 Pearson Education, Inc.

Figure 9.6 P GenerationGenetic makeup (alleles) Alleles carried by parents Gametes Purple flowers PP White flowers pp All P All p p P F 1 Generation (hybrids) F 2 Generation (hybrids) Alleles segregate Gametes Purple flowers All Pp Sperm from F 1 plant Eggs from F 1 plant Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp p p P P PPPp pp

Geneticists distinguish between an organism’s physical appearance and its genetic makeup. –An organism’s physical appearance is its phenotype. –An organism’s genetic makeup is its genotype. Monohybrid Crosses © 2013 Pearson Education, Inc.

Genetic Alleles and Homologous Chromosomes A gene locus is a specific location of a gene along a chromosome. Homologous chromosomes have alleles (alternate versions) of a gene at the same locus. © 2013 Pearson Education, Inc.

Figure 9.7 Homologous chromosomes P Genotype: Gene loci P a aa b B Dominant allele Recessive allele Bb PP Homozygous for the dominant allele Homozygous for the recessive allele Heterozygous with one dominant and one recessive allele a

Mendel’s Law of Independent Assortment A dihybrid cross is the mating of parental varieties differing in two characters. What would result from a dihybrid cross? Two hypotheses are possible: 1. dependent assortment or 2. independent assortment. © 2013 Pearson Education, Inc.

Figure 9.8 F 1 Generation F 2 Generation RRYY Predicted results (not actually seen) P Generation Gametes RY rryy ry (a) Hypothesis: Dependent assortment RrYy RY ry Sperm Eggs RY ry Actual results (support hypothesis) RRYY RY rryy ry RrYy (b) Hypothesis: Independent assortment Gametes RY ry Sperm RY ry Ry rY Ry rY RRYY Rryy RRyy RrYy RRYy RrYy rrYy Rryy rryy RrYY rrYYRrYyrrYy RRYy RrYy Yellow round Yellow wrinkled Green wrinkled Green round

Figure 9.12 DOMINANT TRAITS Free earlobe RECESSIVE TRAITS Widow’s peakFreckles Attached earlobe Straight hairline No freckles

A family pedigree –shows the history of a trait in a family and –allows geneticists to analyze human traits. Family Pedigrees © 2013 Pearson Education, Inc.

Figure 9.13 Female Male Attached Free Female Male First generation (grandparents) Second generation (parents, aunts, and uncles) Third generation (brother and sister) Aaron Ff Betty Ff Cletus ff Debra Ff Evelyn FF or Ff Lisa FF or Ff Fred ff Gabe ff Hal Ff Ina Ff Jill ff Kevin ff

Human Disorders Controlled by a Single Gene Many human traits –show simple inheritance patterns and –are controlled by single genes on autosomes. © 2013 Pearson Education, Inc.

Table 9.1

Recessive Disorders Most human genetic disorders are recessive. Individuals who have the recessive allele but appear normal are carriers of the disorder. © 2013 Pearson Education, Inc.

Figure 9.16 Parents Sperm Eggs d Dwarf D Dd d dd d Normal (no achondroplasia) Molly Jo Dwarf (achondroplasia) Dd dd Normal dd Normal Dwarf Matt Amy Jacob Zachary Jeremy

Genetic Testing Today many tests can detect the presence of disease-causing alleles. Most genetic tests are performed during pregnancy. –Amniocentesis collects cells from amniotic fluid. –Chorionic villus sampling removes cells from placental tissue. Genetic counseling helps patients understand the results and implications of genetic testing. © 2013 Pearson Education, Inc.

The Role of Environment Many human characters result from a combination of –heredity and –environment. Only genetic influences are inherited. © 2013 Pearson Education, Inc.

Figure 9.29b Colorized SEM Y X

Sex Determination in Humans Nearly all mammals have a pair of sex chromosomes designated X and Y. –Males have an X and Y. –Females have XX. © 2013 Pearson Education, Inc.

Sex-Linked Genes Any gene located on a sex chromosome is called a sex-linked gene. –Most sex-linked genes are found on the X chromosome. –Red-green colorblindness is –a common human sex-linked disorder and –caused by a malfunction of light-sensitive cells in the eyes. © 2013 Pearson Education, Inc.

Hemophilia –is a sex-linked recessive blood-clotting trait that may result in excessive bleeding and death after relatively minor cuts and bruises and –has plagued the royal families of Europe. Sex-Linked Genes © 2013 Pearson Education, Inc.