CHAPTER 9 Patterns of Inheritance

Genetic testing –Allows expectant parents to test for possibilities in their unborn child. –Includes amniocentesis and CVS. –Has risks associated with it. Biology And Society: Testing Before Birth

Gregor Mendel –Was the first person to analyze patterns of inheritance. –Deduced the fundamental principles of genetics. Heritable Variation and Patterns of Inheritance

In an Abbey Garden Mendel studied garden peas because –These plants are easily manipulated. –These plants can self-fertilize. Mendel carried out some cross-fertilization

Figure 9.4

He also created true-breeding varieties of plants. Mendel then crossed two different true-breeding varieties.

Mendel’s Law of Segregation Mendel performed many experiments. –He tracked several characteristics in pea plants from which he formulated several hypotheses.

Figure 9.5

Monohybrid Crosses A monohybrid cross is a cross between parent plants that differ in only one characteristic.

Mendel developed four hypotheses from the monohybrid cross: –There are alternative forms of genes, called alleles. –For each characteristic, an organism inherits two alleles, one from each parent. –Alleles can be dominant or recessive. –Gametes carry only one allele for each inherited characteristic.

Mendel’s law of segregation –The two members of an allele pair segregate (separate) from each other during the production of gametes. An explanation of Mendel’s results, including a Punnett square

Figure 9.6b

Phenotype –An organism’s physical traits Genotype –An organism’s genetic makeup

Genetic Alleles and Homologous Chromosomes Homologous chromosomes –Have genes at specific loci. –Have alleles of a gene at the same locus.

Figure 9.7

Homozygous –When an organism has identical alleles for a gene Heterozygous –When an organism has different alleles for a gene

Mendel’s Law of Independent Assortment A dihybrid cross –Is the mating of parental varieties differing in two characteristics.

Figure 9.8

Mendel’s law of independent assortment states that –Each pair of alleles lines up without caring which side its on during gamete formation.

Using a Testcross to Determine an Unknown Genotype A testcross is a mating between –An individual of unknown genotype and a homozygous recessive individual. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Figure 9.10

Figure 9.12

A family pedigree –Shows the history of a trait in a family. –Allows geneticists to analyze human traits.

Figure 9.13

Human Disorders Controlled by a Single Gene Many human traits –Show simple inheritance patterns. –Are controlled by genes on autosomes.

Table 9.1

Recessive Disorders Most human genetic disorders are recessive. –Individuals can be carriers of these diseases.

Dominant Disorders Some human genetic disorders are dominant. –Achondroplasia is a form of dwarfism.

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

ABO Blood Type: An Example of Multiple Alleles and Codominance The ABO blood groups in humans are an example of multiple alleles. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

Sex Chromosomes and Sex-Linked Genes Sex chromosomes –Influence the inheritance of certain traits.

Sex Determination Sex chromosomes –Are designated X and Y. –Determine an individual’s sex.

Sex-Linked Genes Sex-linked genes –Are any genes located on a sex chromosome. –Were discovered during studies on fruit flies.

Inheritance patterns of a sex-linked gene

Sex-Linked Disorders in Humans A number of human conditions result from sex- linked (X-linked) genes.

Red-green color blindness –Is characterized by a malfunction of light-sensitive cells in the eyes.

Hemophilia –Is a blood-clotting disease.