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Mendelian Inheritance of Human Traits. Section 12.1. Pedigrees. A graphic representation of genetic inheritance A set of symbols (see chart on page 309) Male/Female Affected by trait or not Family relationships Carrier-heterozygous . Simple Recessive Heredity.
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Mendelian Inheritance of Human Traits Section 12.1
Pedigrees • A graphic representation of genetic inheritance • A set of symbols (see chart on page 309) • Male/Female • Affected by trait or not • Family relationships • Carrier-heterozygous
Simple Recessive Heredity • Most genetic disorders are caused by recessive alleles • Individual must be homozygous recessive to have disorder • Cystic fibrosis (CF) • Tay-Sachs disease • Phenylketonuria (PKU)
Simple Dominant Heredity Only a single dominant allele is necessary for characteristic Cleft chin Dimples Freckles Widow’s peak Detached earlobes Six fingers Hair on the middle section of fingers Huntington’s disease
When Heredity Follows Different Rules Section 12.2
Incomplete Dominance Appearance of a third phenotype
Codominance Both alleles are expressed equally
Multiple alleles Traits controlled by more than two alleles
Sex determination Autosomes: 22 pairs of homologous chromosomes in humans Sex chromosomes: XY (male) XX (female)
Sex-linked inheritance Traits controlled by genes located on sex chromosomes Written as superscripts on X & Y
Polygenic inheritance Inheritance pattern of a trait that is controlled by two or more genes May be on the same or different chromosomes Each gene may have two or more alleles Use upper & lower case letters Range of variability/phenotypes
External Influences Genetic makeup determines only the potential to develop and function Temperature Nutrition Light Chemicals Infectious agents
Internal Influences Sex influenced expressions-hormones Age
Complex Inheritance of Human Traits Section 12.3
Codominance Sickle-cell amemia Changes shape of red blood cell Results in several blood disorders
Multiple Alleles Phenotype Genotype A AA or AO B BB or BO AB AB O OO Blood types
Sex-Linked Traits Red-green color blindness Hemophilia
Polygenic Inheritance Skin color Height
Changes in Chromosome Numbers Nondisjunction Karyotype–chart of chromosome pairs Down Syndrome-Trisomy 21 Abnormal numbers of sex chromosomes
Gene Frequency Activity andLINCS Tables Assignment for Chapter 12 Codominant allele Incomplete dominance Multiple allele Polygenic inheritance