Essential Questions What are the differences between various complex inheritance patterns? How can sex-linked inheritance patterns be analyzed? How can genetic patterns be analyzed to determine dominant or recessive inheritance patterns? What are examples of dominant and recessive disorders? How can human pedigrees be constructed from genetic information? How do you determine blood types? Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Recessive Genetic Disorders A recessive trait is expressed when the individual is homozygous recessive for the trait. ( r r or t t ) Those with at least one dominant allele will not express the recessive disorder. (Rr or Tt) An individual who is heterozygous for a recessive disorder is called a carrier. Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Recessive Genetic Disorders Cystic fibrosis (1 in 3500) A disorder that affects the mucous-producing glands, digestive enzymes, and sweat glands. Gene that codes for a membrane protein is missing Cystic fibrosis causes mucus excretion that clogs ducts in the pancreas, interrupts digestion, and blocks respiratory pathways in the lungs. No cure – daily lung treatments – mucus thinning drugs – pancreatic enzyme supplements Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Cystic Fibrosis

Recessive Genetic Disorders Albinism 1 in 17,000 Albinism is caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes. Individuals with albinism have very pale skin, white hair, and pink irises. No cure Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Albinism

Albinism

Albinism

Recessive Genetic Disorders Tay-Sachs disease 1 in 2500 Gene is found on chromosome 15 Cherry spot on back of the eye 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. Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Recessive Genetic Disorders Galactosemia 1 in 50,000 Recessive genetic disorder characterized by the inability of the body to digest galactose. Inability to digest milk products Mental disabilities No cure – restrict galactose/lactose OTHERS PKU Autism Muscular Dystrophy Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

PKU-Phenylketonuria

Autism

Muscular Dystrophy

Those that have the disease are homozygous recessive. Dominant Genetic Disorders Those that have the disease are homozygous recessive. r r or b b Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Dominant Genetic Disorders Huntington’s disease 1 in 10,000 Affects the nervous system, causing gradual loss of brain function Progressive break down of nerve cells in the brain. Ability to move deteriorates over time No cure or treatment Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Huntington's Disease

Dominant Genetic Disorders Achondroplasia Causes small body size and limbs that are comparatively short Caused by an abnormal gene that affects bone growth

Achondroplasia

Achondroplasia

The other 22 pairs of chromosomes are called autosomes. Sex Determination One pair of chromosomes, sex chromosomes, determine an individual’s gender. XX: female XY: male The other 22 pairs of chromosomes are called autosomes. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Dosage Compensation Chromosome inactivation Copyright © McGraw-Hill Education Complex Patterns of Inheritance

In female, one X chromosome is inactivated in each cell. 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. In female, one X chromosome is inactivated in each cell. Called dosage compensation or x-inactivation Which X stops working in each cell is random. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

The inactivated X chromosome can be observed in cells. Dosage Compensation Barr bodies The inactivated X chromosome can be observed in cells. Darkly stained, inactivated X chromosomes are called Barr bodies. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Sex-Linked Traits Traits controlled by genes located on the X chromosome are sex-linked traits. Because males have only one copy of the X chromosome, they are more affected by recessive X- linked traits. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Red-green color blindness Recessive, X-linked trait Sex-Linked Traits Red-green color blindness Recessive, X-linked trait Mothers are carriers. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Color Blindness

Color Blindness Video

Recessive, X-linked trait that causes delayed clotting of blood Sex-Linked Traits Hemophilia Recessive, X-linked trait that causes delayed clotting of blood BLEEDER’s DISEASE Normal blood clots in 2-8 minutes Hemophilia take up to 30 minutes Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Hemophilia

Hemophilia

Pedigrees A pedigree is a diagram that traces the inheritance of a particular trait through several generations. Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Analyzing Pedigrees Inferring Genotypes Knowing physical traits can determine what genes an individual is most likely to have. Predicting Disorders Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes. Copyright © McGraw-Hill Education Basic Patterns of Human Inheritance

Incomplete Dominance In some organisms, heterozygous individuals will display the dominant phenotype. With incomplete dominance, the heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Codominance In codominance, both the dominant and recessive alleles are expressed in heterozygous individuals. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Changes in hemoglobin cause red blood cells to become sickle shaped. Codominance Sickle-cell disease Changes in hemoglobin cause red blood cells to become sickle shaped. People who are heterozygous for the trait have both normal and sickle-shaped cells. Sickle-cell disease and malaria Those who are heterozygous for the sickle cell trait also have a higher resistance to malaria. The death rate due to malaria is lower where sickle-cell trait is higher, meaning more people live to pass it on to their offspring. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Sickle Cell Anemia

Multiple alleles can demonstrate a hierarchy of dominance. Coat color of rabbits Multiple alleles can demonstrate a hierarchy of dominance. In rabbits, four alleles code for coat color: C, cch, ch, and c. The hierarchy of dominance is C > cch > ch >c. The presence of multiple alleles increases the possible number of genotypes and phenotypes. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Seen in the coat color of Labrador retrievers Epistasis Epistasis is an interaction where one allele hides the effects of another allele. Seen in the coat color of Labrador retrievers Dominant allele E determines whether the coat will have dark pigment. Allele B determines how dark the coat will be. When a dog has recessive ee alleles, the coat will be yellow, because the e allele masks the effects of the B allele. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Include such traits as skin color, height, and eye color Polygenic Traits Polygenic traits arise from the interaction of multiple pairs of genes. Include such traits as skin color, height, and eye color Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Skin Color

Multiple Alleles Blood groups in humans Some forms of inheritance are determined by more than two alleles, referred to as multiple alleles. The ABO blood group has three forms of alleles, sometimes called AB markers. Copyright © McGraw-Hill Education Complex Patterns of Inheritance

Blood Types About half of us are blood group O Next most common is blood group A. Few people have type B Least common type AB.

Blood Types Phenotype Genotype A AA or Ai B BB or Bi AB O ii

Rh The Rh blood groups are the next most familiar types. People whose red cells have a particular feature called the “ D antigen” are Rh positive. People who lack the factor are Rh negative. Most people are Rh positive.

Who Can You Donate Too? Blood Type Video