1. CHAPTER 4 Heredity and Evolution

2. Gregor Mendel Founder of modern genetics Augustinian friar From what is now the Czech Republic Pea plant studies from 1856-1863 demonstrated the basic concept of inheritance

3. Hybrids Offspring of parents that differ from each other with regard to certain traits or certain aspects of genetic makeup; heterozygotes.

4. Alleles Alternate forms of a gene Can occur at the same locus on a pair of chromosomes and influence the same trait A gene is a stretch of DNA or RNA that determines a certain trait An allele is a fixed spot on a chromosome

5. Dominance and Recessiveness Dominant traits are governed by an allele that can be expressed in the presence of another, different allele. Dominant alleles prevent the expression of recessive alleles in heterozygotes. Recessive traits are not expressed in heterozygotes. For a recessive allele to be expressed, there must be two copies of the allele.

6. Principle of Segregation Discrete units, or genes, occur in pairs because chromosomes occur in pairs. During gamete production, members of each gene pair separate so each gamete contains one member of a pair. During fertilization, the full number of chromosomes is restored and members of a gene or allele pairs are reunited.

7. Traits Mendel Studied in Peas

8. Results When One Trait (Height) Is Considered at a Time

9. Locus and Zygosity The position on a chromosome where a given gene occurs. The term is sometimes used interchangeably with gene, but this usage is technically incorrect. Heterozygous Having different alleles at the same locus on members of a pair of chromosomes. Homozygous Having the same allele at the same locus on both members of a pair of chromosomes.

10. Punnett Square Demonstrates how alleles can be combined when the F1 plants are self- fertilized to produce an F2 generation. Shows that 1/4 of the F2 plants should be homozygous dominant (TT), 1/2 heterozygous (Tt), and the remaining 1/4 to be homozygous recessive (tt).

11. Genotype and Phentype Genotype The genetic makeup of an individual. Can refer to an organism’s entire genetic makeup or to the alleles at a particular locus. Phenotype The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environment.

12. Assortment  Independent  Distribution of one pair of alleles into gametes does not influence the distribution of another pair  Genes controlling different traits are inherited independently of one another  Random  The chance distribution of chromosomes to daughter cells during meiosis  Along with recombination, a source of genetic variation from meiosis

13. Mendelian Traits and Inheritance in Humans  Characteristics that are influenced by alleles at only one genetic locus.  Examples include many blood types, such as ABO.  Many genetic disorders, including sickle- cell anemia and Tay- Sachs disease, are also Mendelian traits.  Human ABO Over 19,000 human trains are known to be inherited according to Mendelian principles  Human ABO blood system  The A and B alleles are dominant to the O allele.  Neither the A or B allele are dominant to one another; they are codominant.  The expression of two alleles in heterozygotes  Neither allele is dominant or recessive  Both influence the phenotype

14. Antigens Large molecules found on the surface of cells. Several different loci govern various antigens on red and white blood cells. Foreign antigens provoke an immune response.

15. Polygenic Inheritance Polygenic traits, or continuous traits, are governed by alleles at two or more loci, and each locus has some influence on the phenotype. Hair, eye and skin color are polygenic traits

16. Skin Color Coloration is determined by pigment produced by specialized cells called melanocytes The amount of melanin produced determines how dark or light skin will be Melanin production is influenced by interactions between several different loci that, until recently had not been identified

17. Polygenic Traits and Racial Classification Polygenic traits account for most of the readily observable phenotypic variation seen in humans Traditionally serve as a basis for racial classification Actually, stature, shape of face, fingerprint patterns are polygenic traits Most can be measured, i.e. height in feet and inches or meters and centimeters

18. Discontinuous Distribution of Mendelian Traits Shows discontinuous distribution of ABO blood type in a hypothetical population. The expression of the trait is described in terms of frequencies.

19. Continuous Expression of a Polygenic Trait Represents the continuous expression of height in a large group of people.

20. Height A group of male students arranged according to height. The most common height is 70 inches, which is the mean, or average, for this group.

21. Mitochondrial Inheritance All cells contain mitochondria that convert energy into a form that can be used by the cell. Animals of both sexes inherit their mtDNA, and all mitochondrial traits, from their mothers. All the variation in mtDNA is caused by mutation, which makes it very useful for studying genetic change over time.

22. The Modern Synthesis Evolution, as it has been considered from the middle of the twentieth century, is a two-stage process: 1. The production and redistribution of variation (inherited differences among organisms). 2. Natural selection acting on this variation, whereby inherited differences, or variation, among individuals differentially affect their ability to successfully reproduce.

23. A Current Definition Of Evolution From a modern genetic perspective, we define evolution as a change in allele frequency from one generation to the next. Allele frequencies are indicators of the genetic makeup of a population, the members of which share a common gene pool. In a population, allele frequencies refer to the percentage of all the alleles at a locus accounted for by one specific allele.

24. Micro and macroevolution Microevolution Small genetic changes that occur within a species. A human example is the variation seen in the different ABO blood types. Macroevolution Large-scale changes that occur in populations after many generations, such as the appearance of a new species (speciation).

25. Factors that Produce and Redistribute Variation Mutation Gene Flow Genetic Drift and Founder Effect Recombination

26. Mutation Mutation is a molecular alteration in genetic material: For a mutation to have evolutionary significance it must occur in a gamete Mutation rates for any given trait are usually low When combined with natural selection, evolutionary changes can occur and can occur more rapidly Only way to produce new genes

27. Gene Flow The exchange of genes between populations. If individuals move temporarily and mate in the new population (leaving a genetic contribution), they don’t necessarily stay there. Consistent feature of human evolution Example: The offspring of U.S. soldiers and Vietnamese women represent gene flow, even though the fathers returned to their native population.

28. Genetic Drift Genetic drift occurs solely because the population is small: Alleles with low frequencies may not be passed to offspring and eventually disappear from the population.

29. Founder Effect Occurs when a small band of “founders” leaves its parent group and forms a colony elsewhere. A new population is established and as long as mates are chosen within this population, all the members will be descended from the founders. A once rare allele that was carried by even one of the founders can eventually become common.

30. Recombination The production of offspring with combinations of traits that differ from those found in either parent Doesn’t change allele frequencies, or cause evolution Changes the composition of parts of chromosomes Affects how some genes act, and slight changes of gene function can become material for natural selection to act upon

32. Natural Selection Natural selection provides directional change in allele frequency relative to specific environmental factors. If the environment changes, selection pressures also change. If there are long-term environmental changes in a consistent direction, then allele frequencies should also shift gradually each generation.

33. Sickle-cell Anemia A severe inherited hemoglobin disorder in which red blood cells collapse when deprived of oxygen. It results from inheriting two copies of a mutant allele. This mutation is caused by a single base substitution in the DNA.

34. Why It Matters Many human disorders are caused by mutations in genes at one locus. The more we know about Mendelian disorders, the better prepared we are to make decisions due to a family history of genetic difficulties.