Patterns of Inheritance Chapter 9 Part 2

9.4 Complex Variations in Traits  A trait that is influenced by the products of multiple genes often occurs in a range of small increments of phenotype (continuous variation)  The more genes and other factors that influence a trait, the more continuous the distribution of phenotype

Continuous Variation  Continuous variation A range of small differences in a shared trait  Bell curve Curve that typically results when range of variation in a continuous trait is plotted against frequency in a population

Continuous Variation (Bell Curve)

Fig. 9-12a, p. 165

Fig. 9-12b, p. 165

Animation: Continuous variation in height

Environmental Effects on Phenotype  Enzymes and other gene products control steps of most metabolic pathways  Mutations, interactions among genes, and environmental conditions can affect one or more steps, and contribute to variation in phenotypes

Environmental Effects on Animal Phenotypes  Snowshoe hare in summer and winter  Daphnia without and with predators

Fig. 9-13a, p. 166

Fig. 9-13b, p. 166

Fig. 9-13c, p. 166

Environmental Effects on Plant Phenotypes

Fig. 9-14, p Height (centimeters) 000 A Plant grown at high elevation (3,060 meters above sea level) B Plant grown at mid-elevation (1,400 meters above sea level) C Plant grown at low elevation (30 meters above sea level)

Animation: Coat color in the Himalayan rabbit

9.5 Human Genetic Analysis  Inheritance patterns in humans are studied by following inherited genetic disorders through generations and graphing results as pedigrees  Pedigree Chart showing the pattern of inheritance of a gene in a family

Pedigree: Polydactyly

Fig. 9-15, p. 167 marriage/mating female male offspring individual showing trait being studied sex not specified generation A Standard symbols used in pedigrees *Gene not expressed in this carrier. B A pedigree for polydactyly, which is characterized by extra fingers, toes, or both. The black numbers signify the number of fingers on each hand; the blue numbers signify the number of toes on each foot.

marriage/mating female male offspring individual showing trait being studied sex not specified generation A) Standard symbols used in pedigrees B) A pedigree for polydactyly, which is characterized by extra fingers, toes, or both. The black numbers signify the number of fingers on each hand; the blue numbers signify the number of toes on each foot. Fig. 9-15, p. 167 *Gene not expressed in this carrier. Stepped Art

Animation: Pedigree diagrams

Genetic Abnormalities and Disorders  Genetic abnormality An uncommon version of a heritable trait that does not result in medical problems  Genetic disorder A heritable condition that results in a syndrome of mild or severe medical problems  Syndrome Set of symptoms characterizing a genetic disorder

9.6 Human Genetic Disorders  Some dominant or recessive alleles on autosomes or the X chromosome are associated with genetic abnormalities or disorders  An autosomal dominant allele is expressed in homozygotes and heterozygotes  An autosomal recessive allele is expressed only in homozygotes

Some Autosomal Dominant Disorders

Autosomal Dominant Inheritance

Fig. 9-16a, p. 168 normal mother affected father meiosis and gamete formation affected child normal child disorder-causing allele (dominant)

Fig. 9-16b, p. 168

Animation: Autosomal-dominant inheritance

Some Autosomal Recessive Disorders

Autosomal Recessive Inheritance

Fig. 9-17a, p. 169 carrier mothercarrier father meiosis and gamete formation affected child carrier child normal child disorder-causing allele (recessive)

Animation: Autosomal-recessive inheritance

X-Linked Recessive Disorders  Alleles on the X chromosome are inherited and expressed differently in males and females  Males cannot transmit a recessive X-linked allele to their sons  Females pass X-linked alleles to male offspring Example: Queen Victoria of England and hemophilia

Some X-Linked Recessive Disorders

X-Linked Recessive Inheritance

Fig (top), p. 170

Fig (a-d), p. 170

Animation: X-linked inheritance

An X-Linked Trait: Queen Victoria and Hemophilia

Animation: Morgan’s reciprocal crosses

Video: ABC News: Genetic testing: Screening embryos for disease

9.7 Changes in Chromosome Number  Chromosome number can change permanently, usually resulting from nondisjunction  Nondisjunction Failure of duplicated chromosomes (sister chromatids) or homologous chromosomes to separate during meiosis or mitosis

Nondisjunction During Meiosis

Fig. 9-20a, p. 172 Metaphase IAnaphase ITelophase IMetaphase IIAnaphase IITelophase II

Fig. 9-20b, p. 172 Stepped Art Metaphase I Anaphase I Telophase I Metaphase II Anaphase II Telophase II

Aneuploidy  Aneuploidy A chromosome abnormality in which a cell has too many or too few copies of a particular chromosome (trisomy, monosomy)  The most common aneuploidy in humans, trisomy 21, causes Down syndrome

Some Disorders Caused by Aneuploidy

Polyploidy  Autosomal aneuploidy is usually fatal in humans, but many flowering plants, and some insects, fishes and other animals are polyploid  Polyploid Having three or more of each type of chromosome characteristic of the species

Autosomal Change and Down Syndrome  Trisomy 21 (Down syndrome) The only autosomal trisomy that allows humans to survive to adulthood Affected individuals tend to have certain physical features and impairments  Nondisjunction leading to trisomy 21 increases with age of the mother

Autosomal Change and Down Syndrome

Fig. 9-20b, p. 172

Fig. 9-20c, p. 172

Sex Chromosome Abnormalities  Usually associated with learning difficulties, speech delays, and motor skill impairment  Female sex chromosome abnormalities: Turner syndrome (XO), XXX syndrome  Male sex chromosome abnormalities: Klinefelter syndrome (XXY); XYY syndrome

Turner’s Syndrome (XO)  Affects development of ovaries, sexual maturity

Animation: Nondisjunction

9.8 Some Prospects in Human Genetics  Geneticists estimate the chance that a couple’s offspring will inherit a genetic abnormality or disorder  Potential parents who may be at risk of transmitting a harmful allele to offspring have screening or treatment options

Prenatal Diagnosis  Tests performed before birth Amniocentesis Chorionic villi sampling (CVS) Fetoscopy  Carry risks of miscarriage or injury to fetus

Amniocentesis  Risks of puncture, infection, loss of amniotic fluid

Animation: Amniocentesis

Fetoscopy  Increased risk of miscarriage

Preimplantation Diagnosis  A single cell taken from an embryo produced by in vitro fertilization is tested before implantation

Genetic Screening and Phenotypic Treatments  Genetic screening Hospitals routinely screen newborns for certain genetic disorders such as PKU (Phenylketonuria)  Phenotypic treatments Surgery, prescription drugs, hormone replacement therapy, or dietary controls can minimize symptoms of some genetic disorders

9.9 Impacts/Issues Revisited  The cystic fibrosis (CF) allele is very common in some populations  The CF allele is lethal in homozygotes, but offers heterozygotes some protection against bacterial diseases such as typhoid fever

Digging Into Data: Cystic Fibrosis and Typhoid Fever