Chapter 11: Complex Inheritance and Human Heredity

1. Chapter 11: Complex Inheritance and Human Heredity Section 11.1: Basic Patterns of Human Inheritance Section 11.2: Complex Patterns of Inheritance Section 11.3: Chromosomes and Human Heredity

2. Recessive Genetic Disorders • Dr. Archibald Garrod, an English physician, became interested in a disorder linked to an enzyme deficiency called alkaptonuria, which results in black urine and runs in families. • A recessive trait is expressed when the individual is homozygous recessive for the trait. • Therefore, those with at least one dominant allele will not express the recessive trait. • An individual who is heterozygous for a recessive disorder is called a carrier

3. Recessive Genetic Disorders

4. Cystic Fibrosis • Affects the mucus-producing glands, digestive enzymes, and sweat glands • Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat. • Without sufficient chloride ions in the cells, a thick mucous is secreted.

5. Albinism • Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes • White hair • Very pale skin • Pink pupils

6. Tay-Sachs Disease • Diagnosed by “cherry-red” spot at the back of the eye • Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides. • Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration. • Affects people of Jewish descent

7. Galactosemia • Recessive genetic disorder characterized by the inability of the body to digest galactose. • Sufferers should avoid milk products Lactase

8. Dominant Genetic Disorders • Caused by dominant alleles • Those who do not have the disorder are homozygous recessive. • Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short

9. Achondroplasia • Small body size • Short limbs • Usually born to parents of normal size

10. Huntington’s disease • Affects nervous system • Appears between ages of 30-50

11. Pedigrees • A diagram that traces the inheritance of a particular trait through several generations.

12. Pedigrees • Inferring Genotypes • Knowing physical traits can determine what genes an individual is most likely to have. • Predicting Disorders • Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes.

13. 11.2 Complex Patterns of Inheritance • Main idea-Complex inheritance of traits does not follow inheritance patterns described by Mendel

14. Incomplete Dominance • The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.

15. Codominance • Both alleles are expressed in the heterozygous condition • Example • Sickle-cell Disease • Changes in hemoglobin cause red blood cells to change to a sickle shape • People who are heterozygous for the trait have both normal and sickle-shaped cells

16. Malaria and Sickle-cell • Areas with high instance of malaria overlap with high frequency of the sickle-cell gene • Death rate from malaria is lower where sickle-cell gene is higher

17. Multiple Alleles • Blood groups in humans • ABO blood groups have three forms of alleles

18. Epistasis • Variety is the result of one allele hiding the effects of another allele. eebb eeB_ E_bb E_B_ No dark pigment present Dark pigment present

19. Sex Determination • Sex chromosomes determine an individual’s gender • Pair 23 determines sex • The rest of the chromosomes are autosomes

20. Dosage Compensation • The X chromosome carries a variety of genes that are necessary for the development of both females and males • The Y has genes that relate mostly to male characteristics • In females extra genetic material is gotten rid of through dosage compensation

21. Chromosome Inactivation

22. Sex-linked Traits • Genes located on the X chromosome • Since males have only one chromosome, they are affected by recessive X-linked traits more often than are females • Red-green color blindness • Hemophilia

23. Polygenic Traits • Polygenic traits arise from the interaction of multiple pairs of genes • Skin color, height, eye color, and fingerprint pattern

24. Environmental Influences • Environmental factors affect phenotype • Diet and exercise • Sunlight and water • Temperature

25. Twin Studies • Helps scientists separate genetic contributions from environmental contributions. • Traits that appear frequently in identical twins are at least partially controlled by heredity. • Traits expressed differently in identical twins are strongly influenced by environment

26. Karyotype Studies • Karyotype-micrograph in which the pairs of homologous chromosomes are arranged in decreasing size • Images of chromosomes stained during metaphase • Chromosomes are arranged in decreasing size to produce a micrograph • 22 autosomes are matched together with one pair of nonmatching sex chromosomes

27. Telomeres • Protective caps consist of DNA associated with proteins • Serves a protective function for the structure of the chromosome • Might be involved in both aging and cancer

31. Nondisjunction • Sister chromatids fail to separate properly • Results in extra copy of chromosome or only one copy of a chromosome • Having a set of three chromosomes is trisomy • Having only one copy of a chromosome is monosomy • Down Syndrome – Trisomy 21 • Distinctive facial features, short stature, heart defects, and mental disability

33. Nondisjunction • Sex Chromosomes • XX – Normal female • XO – Female with Turner’s Syndrome • XXX – Nearly normal female • XY – Normal male • XXY – Male with Klinefelter’s Syndrome • XYY – Normal or nearly normal male • OY – Results in death

34. Fetal Testing • Used to diagnosis genetic disorders before birth • Amniocentesis • Benefits-diagnosis of chromosome abnormalities and other defects • Risks-discomfort for expectant mother, slight risk of infection, and risk of miscarriage • Chorionic villus sampling • Benefits-diagnosis of chromosome abnormalities and certain genetic defects • Risks-miscarriage, infection, and newborn limb defects • Fetal blood sampling • Benefits-diagnosis of genetic or chromosomal abnormality, checks for fetal problems and oxygen levels, and medications can be given to the fetus before birth • Risks-bleeding from sample site, infection, amniotic fluid might leak, and fetal death