CHAPTER 9 Patterns of Inheritance Biology And Society

CHAPTER 9 Patterns of Inheritance

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

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

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 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. 6 b

• 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 sexlinked (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.