Chapter 9 Patterns of Inheritance

Section 9.1 – History of Genetics Hippocrates – Father of Medicine –Suggested the idea of “pangenesis” The idea that “pangenes” travel from each part of an organism’s body to the eggs or sperm and are passed to the next generation Aristotle – Greek Philosopher –Rejected “pangenesis” saying that particles are not inherited only the potential to produce certain body features

Section 9.1 – History of Genetics Why pangenesis is wrong: –Reproductive cells are not composed of particles of somatic cells –Changes in somatic cells do not influence egg or sperm Just because you lift weights and get bigger muscles does not mean that your sperm and egg will contain genes for big muscles

Section 9.2 – Gregor Mendel Augustinian monk that discovered the principles of genetics Lived in Austria in the 1800s Argued that parents pass “heritable factors” on to their offspring Studied how traits were passed from generation to generation in garden pea plants (Pisum sativum)

Section 9.2 – Why pea plants? Easy to grow Come in many different varieties –Tall / Dwarf –Purple Flowers / White Flowers –Yellow Peas / Green Peas –Round Peas/ Wrinkled Peas –Inflated Pods/ Constricted Pods –Green Pods/ Yellow Pods Mendel was able to control the matings

Figure 9.2C Mendel’s technique for cross- fertilization of pea plants

Section 9.2 Self-fertilization (self-pollination) –When a plant transfers pollen from its own male parts to its female part

Section 9.2 Cross-fertilization (cross-pollination) –When a plant transfers pollen its male parts to another, different plant’s female part

Section 9.2 The Seven Pea Characteristics Studied by Mendel

Section 9.3 – A Mendelian Monohybrid Cross

Section 9.3 Homozygous –Having the same alleles for a gene –Also known as true-breeding or purebreed –Can be homozygous dominant (such as BB) or homozygous recessive (such as bb) Heterozygous –Having different alleles for a gene –Also known as hybrid –For example: Bb

Section 9.3 Mendel’s Hypotheses There are alternate forms of genes. (These are now called “alleles”) For each inherited characteristic, an organism has two genes, one from each parent. These genes may be both the same allele or different alleles. A sperm or egg carries only one allele for each inherited trait, because allele pairs separate from each other during the production of gametes. When the two genes of a pair are different alleles and one is fully expressed while the other has no noticeable effect on the organism’s appearance. These alleles are called the dominant allele and recessive alleles.

Section 9.4 Alleles –Alternate forms of a gene that are on the same location (locus…plural: loci) on homologous chromosomes

Section 9.4 Dominant alleles are always represented by a CAPITAL letter Recessive alleles are always represented by a lowercase letter –Must be the same letter as the Dominant allele

Section 9.3 Genotype –Term that refers to the alleles an individual has for a trait For example, Mrs. Castone is “bb” for eye color Phenotype –Term that refers to the outward appearance an individual has for a trait For example, Mrs. Castone has blue eyes

Section 9.3 Monohybrid Cross –A breeding in which two parents are crossed in order to look at one different characteristic or trait.

Section 9.3 – Principle of Segregation & Principle of Independent Assortment

Section 9.5 Dihybrid cross –A breeding in which two parents are crossed in order to look at two different characteristics or traits.

Section 9.6 Test- Cross –A technique used to find the genotype (homozygous or heterozygous) of an individual that displays a dominant trait –The individual whose genotype is not known is crossed with a homozygous recessive individual

Section 9.6 – Test Cross

Section 9.7 Probability –The odds or chance that a certain event if going to occur –Expressed as a percent or a fraction –In genetics, the probability of a certain genotype or phenotype can be solved if the parents’ genotypes are known.

Section 9.8 Pedigree – A family tree that is used to trace the inheritance of human genes Males are represented by squares Females are represented by circles A shaded in square/circle = someone with the trait Children are in birth order from left to right

Section 9.8 – Pedigree Example

Section 9.8 – Pedigree Inheritance If a trait or disease is autosomal dominant… –Every generation in the pedigree is likely to have it If a trait or disease is autosomal recessive… –It will most likely skip generations If a trait or disease is sex-linked… –A significant amount of boys will have it over girls

Section 9.9 – Recessive Disorders Person must receive a recessive allele from his/her Mom and a recessive allele from his/her Dad Examples: –Sickle cell anemia Misshapen red blood cells which cause person great pain –Cystic Fibrosis Lack of chloride channels in lung tissue causes buildup of mucus and other symptoms

Section 9.9 – Dominant Disorders Person must receive a dominant allele from one parent in order to have the disorder Examples: –Achondroplasia (dwarfism) –Huntington’s Disease Deteriorating neurological disorder –Alzheimer’s Disease

Section 9.12 – Incomplete Dominance The dominant trait is “blended” with the recessive trait in a hybrid (heterozygote)

Section 9.13 – Multiple Alleles Instead of having a dominant and a recessive allele, some traits have more than 2 alleles –Example: Human Blood Types

Section Codominance When two alleles can be dominant together. Both get capital letters and both are expressed. –Examples: The flower below exhibits both red and white colors; A person with AB blood type has codominance

Section Pleiotropy When a single gene causes multiple phenotypic traits

Section 9.16 – Polygenic Inheritance “Poly” = Many; “genic” = genes Occurs when 2 or more genes determine a single trait –Examples: Human skin color, Human height, human weight, Human eye colors like green & hazel

Section 9.17 – Chromosome Theory Developed in the 1900s States that genes are located on chromosomes And that behavior of chromosomes during meiosis and fertilization determine inheritance patterns

Section 9.18 – Linked Genes The closer that two genes are together on a chromosome, the more likely they will be inherited together Which traits below would most likely be inherited together in the fruit fly?

Section 9.22 – Sex-linked Traits Sex-linked means “X-linked” Refers to traits found ONLY on the X chromosome More likely to be seen in males than females. Why?

Section 9.22 – Sex-linked Traits Some examples of sex-linked (X-linked) diseases –Hemophilia Causes unstoppable bleeding Was common in the royal family of Russia –Red-green color blindness Red and green colors appear gray –Duchenne muscular dystrophy Progressive weakening and loss of muscle tissue