Inheritance Principles and Human Genetics

1. Inheritance Principlesand Human Genetics BioH - Chapter 11

2. Genetics Vocabulary Review Genes – units of information about heritable traits Homologous chromosomes – similar chromosomes received from male and female that line up next to each during MetaphaseI in meiosis Alleles – different forms of a gene Locus – location on a chromosome where specific genes are found Linkage – when genes on a chromosome “stay together” even during crossing-over Genetic recombination – the “recombining” of genes as a result of crossing-over

3. Chromosomes • Thomas Hunt Morgan • Studied fruit flies • Found X and Y chromosomes

4. Karyotypes Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner

5. Sex chromosomes (X, Y) • Contain genes that determine the sex (gender) of an individual • Autosomes • Not directly involved in determining the sex of an individual • Different organisms, different number X Y

6. Sex determination • Sperm has equal chance of receiving X or Y • Egg only receives X • XX – female • XY - male • Totally RANDOM process • Sex-determination Region Y (SRY) • Found in mammalian Y chromosome • Gene codes protein to cause gonads to develop testes

7. Gene location • Sex-linked • Traits coded for by an allele on a sex chromosome • Could be on X or Y chromosome • More X-linked genes because X is much larger • If male carries a recessive allele on the X chromosome, it will exhibit the trait • Ex. Hemophilia (blood disorder)

8. Linked genes • Traits that are inherited together • Makes a linkage group • This happens because they are found close to each other in the same chromosome and not as easily genetically recombined by “crossing-over”

9. Chromosome Map • A diagram that shows the linear order of genes on a chromosome • Map unit – frequency of crossing over of 1%.

10. Mutations • Germ-cell mutations • Occur in gametes (may not be expressed until offspring) • Somatic-cell mutations • Occur in body cells • May affect organs • Skin cancer and leukemia • Lethal mutations • Cause death, often before birth

11. Inheritance of Traits • Pedigrees • A diagram showing how a trait is inherited over several generations

12. Russian Royal Family & hemophilia Genetic abnormality – rare, uncommon trait version Genetic disorder – inherited condition causing medical disorders Syndrome – recognized set of disorders that characterize a disorder

13. Patterns of Inheritance • If a trait is • Autosomal • Appears in both sexes equally • Dominant • Every individual with the trait will have parents with the trait • BB or Bb (dominant trait will show) • bb (recessive trait will show) • Recessive • 1, 2, or no parent with the trait • Bb X Bb will not show mutation but can produce children for the recessive allele (bb) • Bb (carrier)

14. Genetic Trait and Disorders • Single-Allele traits • Controlled by a single allele of a gene • More 200 human traits • Huntington’s disease • Forgetfulness and irritability

15. Gene Inheritance & Disorders • Polygenic Inheritance • Traits are influence by more than one gene • Skin color • 3 to 6 genes • Genes control amount of melanin • Eye color, height, hair color

16. Complex characters • Influenced both by environment and genes • Skin color, breast cancer, height

17. Multiple Alleles • Genes with 3 or more alleles • ABO blood groups • IA, IB, and I • IA and IBare codominant • Codominance • Both alleles are expressed • IAIBis type AB

18. Incomplete dominance • Trait that is displayed is intermediate between the two parents. • Hair type • Curly (CC) X Straight (cc)= Wavy hair (Cc)

19. X-linked • Genes are linked to x-chromosome • Colorblindness • Recessive • Unable to distinguish certain colors, eg. green or red

20. Sex-influence traits • Males and females can show different phenotypes even with same genotypes • Autosomal • Type of Baldness • Dominant in males • Recessive in females

21. Chromosomal disorders Chromosome problems, not genes Duplication – a repeat of several gene sequences on the same chromosome Deletion – loss of a chromosome segment

22. Inversion – gene sequence separated from chromosome, reinserted into same place, but in reverse Translocation – transfer of one chromosome part to a non-homologous chromosome

23. Chromosome number disorders Nondisjunction – one or more pairs of chromosomes fail to separate during mitosis or meiosis (produces condition known as aneuploidy – more or less chromosomes than the parental number) Down Syndrome – one extra chromosome at #21

24. Sex Chromosome number changes • Turner syndrome – inheriting only one X chromosome with no additional X or Y chromosome • Most X0 zygotes • spontaneously abort • 0.01–0.04% of • females • Non-functional ovaries • (infertile) • Short height • Normal intelligence

25. Kleinfelter Syndrome – one extra X chromosome with normal XY (XXY) • 0.05-0.2% of males • Conditions develop after puberty • Smaller testes - usually sterile (not always) • Taller than normal • Normal intelligence • Very subtle phenotype characteristics

26. XYY Condition – extra Y chromosome as result of non-disjunction • 0.1% of males • Taller than average • Mild retardation

27. Detection • Amnioncentesis • Removal of amniotic fluid from the amnion, the sac surrounding the fetus • Between 14 – 16 week of pregnancy

28. Chorionic villi sampling • Cells derived from the zygote that grow between uterus and placenta • Between 8th and 10th week

29. Genetic counseling • Informing a person or couple about their genetic makeup • Form of medical guidance about problems that might affect their offspring

30. Treatment • Usually treat symptoms • Gene therapy • Replacement of defective genes with a healthy one • Somatic cell gene therapy (body cells) • Germ cell gene therapy (eggs or sperms) • Poses risks and ethical issues