© 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

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.

Figure 9.1

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.

Figure 9.2 Carpel (produces eggs) Stamen (makes sperm- producing pollen) Petal

Figure Removed stamens from purple flower. Stamens Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel 21

Figure Removed stamens from purple flower. Stamens Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel Pollinated carpel matured into pod. 321

Figure Removed stamens from purple flower. Stamens Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel Offspring (F 1 ) Pollinated carpel matured into pod. Planted seeds from pod. 4321

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

Figure 9.4a

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

Blast Animation: Single-Trait Crosses Select “Play”

Figure Purple flowers White flowers P Generation (purebred parents)

Figure Purple flowers F 1 Generation White flowers P Generation (purebred parents) All plants have purple flowers

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

Figure 9.5a

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.

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

Dominant traits are not necessarily –normal or –more common. Wild-type traits are –those seen most often in nature and –not necessarily specified by dominant alleles. Family Pedigrees © 2013 Pearson Education, Inc.

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.

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 9.14 Parents Offspring Dd Hearing Dd Sperm Eggs D Hearing D Dd d Hearing (carrier) DD Dd Hearing (carrier) dd Deaf d

Cystic fibrosis is –the most common lethal genetic disease in the United States and –caused by a recessive allele carried by about one in 31 Americans. Recessive Disorders © 2013 Pearson Education, Inc.

Dominant Disorders Some human genetic disorders are dominant. –Achondroplasia is a form of dwarfism. –Huntington’s disease, which leads to degeneration of the nervous system, does not usually begin until middle age. © 2013 Pearson Education, Inc.

Figure 9.15

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

Figure 9.16a Parents Sperm Eggs d Dwarf D Dd d dd d Normal (no achondroplasia) Dwarf (achondroplasia) Dddd Normal dd Normal Dwarf

Figure 9.16b Molly Jo 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.

VARIATIONS ON MENDEL’S LAWS Some patterns of genetic inheritance are not explained by Mendel’s laws. © 2013 Pearson Education, Inc.

Incomplete Dominance in Plants and People In incomplete dominance, F 1 hybrids have an appearance between the phenotypes of the two parents. © 2013 Pearson Education, Inc.

Figure RRrr P Generation Gametes Red White R r

Figure F 1 Generation RRrr Gametes P Generation Gametes Red White R r Rr Pink R r

Figure F 1 Generation RRrr Gametes P Generation F 2 Generation Sperm Gametes Red White R r Rr Pink R r R r R r RRRr rr Rr Eggs

ABO Blood Groups: An Example of Multiple Alleles and Codominance The ABO blood groups in humans are an example of multiple alleles. The immune system produces blood proteins called antibodies that bind specifically to foreign carbohydrates. © 2013 Pearson Education, Inc.

If a donor’s blood cells have a carbohydrate (A or B) that is foreign to the recipient, the blood cells may clump together, potentially killing the recipient. The clumping reaction is the basis of a blood- typing lab test. The human blood type alleles I A and I B are codominant, meaning that both alleles are expressed in heterozygous individuals who have type AB blood. ABO Blood Groups: An Example of Multiple Alleles and Codominance © 2013 Pearson Education, Inc.

Figure 9.20 Blood Group (Phenotype) O Genotypes Antibodies Present in Blood Red Blood Cells Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left A B AB O A B ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Anti-A Anti-B Anti-A Anti-B —

Figure 9.20a Blood Group (Phenotype) GenotypesRed Blood Cells O A B AB ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Antibodies Present in Blood Anti-B Anti-A Anti-A Anti-B —

Figure 9.20b O Blood Group (Phenotype) Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left A B AB B O A

Figure 9.20c

Pleiotropy and Sickle-Cell Disease Pleiotropy is when one gene influences several characters. Sickle-cell disease –exhibits pleiotropy, –results in abnormal hemoglobin proteins, and –causes disk-shaped red blood cells to deform into a sickle shape with jagged edges. © 2013 Pearson Education, Inc.

Figure 9.21 Sickled cells can lead to a cascade of symptoms, such as weakness, pain, organ damage, and paralysis. Abnormal hemoglobin crystallizes into long flexible chains, causing red blood cells to become sickle-shaped. Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Colorized SEM

Figure 9.21a

Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotype. © 2013 Pearson Education, Inc.

Figure 9.22 F 1 Generation P Generation F 2 Generation Sperm Eggs Fraction of population aabbcc (very short) AABBCC (very tall) AaBbCc (medium height)  short allele  tall allele Very shortVery tall Adult height

Figure 9.22a F 1 Generation P Generation aabbcc (very short) AABBCC (very tall) AaBbCc (medium height)  short allele  tall allele

Figure 9.22b  short allele  tall allele F 2 Generation

Figure 9.22c Fraction of population Very shortVery tall Adult height

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

THE CHROMOSOMAL BASIS OF INHERITANCE The chromosome theory of inheritance states that –genes are located at specific positions (loci) on chromosomes and –the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns. © 2013 Pearson Education, Inc.

THE CHROMOSOMAL BASIS OF INHERITANCE It is chromosomes that –undergo segregation and independent assortment during meiosis and –account for Mendel’s laws. © 2013 Pearson Education, Inc.

SEX CHROMOSOMES AND SEX-LINKED GENES Sex chromosomes influence the inheritance of certain traits. For example, humans that have a pair of sex chromosomes designated –X and Y are male or –X and X are female. © 2013 Pearson Education, Inc.

Figure 9.29 Male Female Sperm Egg Offspring FemaleMale Y X 44  XY 44  XX 22  X 22  Y 22  X 44  XX 44  XY Somatic cells Colorized SEM

Figure 9.29a Male Female Sperm Egg Offspring Female Male 44  XY 44  XX 22  X 22  Y 22  X 44  XX 44  XY Somatic cells

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.

Figure 9.30

Figure 9.UN01 Meiosis Haploid gametes (allele pairs separate) Diploid cell (contains paired alleles, alternate forms of a gene) Diploid zygote (contains paired alleles) Gamete from other parent Alleles Fertilization

Figure 9.UN02 Phenotype Genotype Conclusion Recessive Dominant pp P ? All dominant or Unknown parent is PP 1 dominant : 1 recessive Unknown parent is Pp

Figure 9.UN03 Dominant phenotype (RR) Recessive phenotype (rr) Intermediate phenotype (incomplete dominance) (Rr)

Figure 9.UN04 Pleiotropy Multiple traits (e.g., sickle-cell disease) Single gene

Figure 9.UN05 Multiple genes Polygenic inheritance Single trait (e.g., height)

Figure 9.UN06 Female Somatic cells Male 44  XY 44  XX

Figure 9.UN07