chapter 9 patterns of inheritance. genetic testing –allows expectant parents to test for...
TRANSCRIPT
CHAPTER 9CHAPTER 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, F1 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.