Chapter 9 Patterns of Inheritance Power Point Lectures

Chapter 9 Patterns of Inheritance Power. Point® 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 Lectures by Edward J. Zalisko © 2013 Pearson Education, Inc.

Biology and Society: Our Longest-Running Genetic Experiment: Dogs • 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. © 2013 Pearson Education, Inc.

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

In an Abbey Garden • 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. © 2013 Pearson Education, Inc.

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

In an Abbey Garden • 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. © 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 Dominant Pod shape Flower color Purple White Flower position Seed color Seed shape Dominant Recessive Axial Terminal Yellow Green Round Wrinkled Pod color Inflated Recessive Constricted Green Yellow Tall Dwarf Stem length

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

Figure 9. 5 -3 P Generation (purebred parents) Purple flowers White flowers F 1 Generation All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 Generation 3 4 of plants have purple flowers 1 4 of plants have white flowers

Monohybrid Crosses • 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. © 2013 Pearson Education, Inc.

Monohybrid Crosses 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. © 2013 Pearson Education, Inc.

Monohybrid Crosses 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. © 2013 Pearson Education, Inc.

Monohybrid Crosses 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. © 2013 Pearson Education, Inc.

Monohybrid Crosses • 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. © 2013 Pearson Education, Inc.

Figure 9. 6 P Generation Genetic makeup (alleles) Purple flowers Alleles carried PP by parents Gametes White flowers pp All P F 1 Generation (hybrids) Purple flowers All Pp Alleles segregate Gametes 1 P 2 F 2 Generation (hybrids) 1 p 2 Sperm from F 1 plant Eggs from F 1 plant P p PP Pp Pp pp P p Phenotypic ratio Genotypic ratio 3 purple : 1 white 1 PP : 2 Pp : 1 pp

Monohybrid Crosses • 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. © 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 Gene loci Genotype: Dominant allele P a B P a b PP Homozygous for the dominant allele aa Homozygous for the recessive allele Bb Recessive allele Heterozygous with one dominant and one recessive allele

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 (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent assortment P Generation RRYY rryy RRYY Gametes RY ry F 1 Generation rryy ry Rr. Yy Sperm F 2 Generation 1 4 RY 1 4 r. Y 1 4 Ry 1 4 ry Sperm 1 2 RY 1 2 1 4 RY ry 1 2 RY Eggs 1 2 ry Predicted results (not actually seen) 1 4 r. Y Eggs 1 4 Ry 1 4 ry RRYY Rr. YY RRYy Rr. YY rr. YY Rr. Yy rr. Yy RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Actual results (support hypothesis) 9 16 Yellow round 3 16 Green round 3 16 Yellow wrinkled 1 16 Green wrinkled

DOMINANT TRAITS Figure 9. 12 Widow’s peak Free earlobe No freckles Straight hairline Attached earlobe RECESSIVE TRAITS Freckles

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

Figure 9. 13 First generation (grandparents) Second generation (parents, aunts, and uncles) Third generation (brother and sister) Aaron Ff Betty Ff Evelyn Fred Gabe Hal FF ff ff Ff or Ff Kevin ff Female Male Attached Female Male Free Cletus ff Ina Ff Lisa FF or Ff Debra Ff Jill 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 Normal (no achondroplasia) dd Dwarf (achondroplasia) Dd d Sperm D d Dd Dwarf dd Normal Eggs d Jeremy Molly Jo Jacob Zachary Matt Amy

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. 29 b X Colorized SEM Y

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.

Sex-Linked Genes • 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. © 2013 Pearson Education, Inc.