Chapter 15: The Chromosomal Basis of Inheritance

1. Chapter 15:The ChromosomalBasis of Inheritance

2. Important Point: If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!

3. Chromosomal Basis of Inheritance

4. Independent Assortment

5. Independent Assortment “Notice… that one-half of the offspring are expected to inherit a phenotype that matches one of he parental types.” p. 278, Campbell & Reece (2005)

6. Parental Types Special dihybrid with b+ and vg+ on same chro-mosome Recessive “Blank Slate” Parental Types Recombinant Types 2-Locus Test Cross “Expected” assumes Independent Assortment

7. Deviation from Expected

8. Linkage Parental types Basis of recombinant types

9. Frequency of Recombination Complete linkage give frequency of recombination of 0% Frequency of recombination Note that max = 50% (which occurs when loci are either on separate chromosomes or very far apart on the same chromosome) Note that it is the recombinant types that there are fewer or Recombinant types

10. Constructing Genetic Maps Linkage means that two loci are found on the same chromosome Ordering loci on chromosomes Best way to interpret this data is that b and vg are about twice as far apart as b is from cn or cn is from vg. Hence, cn must be in the middle

11. >50% frequencies of recombination are produced by adding together smaller frequencies of recombination Linkage Maps Know what a linkage map is

12. Constructing Genetic Maps

13. Alternative Systems

14. Sex-Linkage Recessives (in mammals) e.g., some forms of hemophilia e.g., some forms of color blindness e.g., Duschenne muscular distrophy Male genotype 100% controlled by what is in the egg Differences 100% dependent on what is in the egg

15. Male Parent Affected

16. Female Parent Carrier Males are more likely affected by recessive alleles, females by dominant alleles

17. Both (female carrier & male affected) Males express the genotype regardless of whether it is dominant or recessive

18. Sex-Linkage Inheritance Patterns Dominant or Recessive Sex-Linked Inheritance?

19. Hemophilia in the Russian Royal Family

20. Barr Bodies & Dosage Compensation One X chromosome is inactivated, to form what is known as a Barr body; this assures that both men and women have the same number of active X chromosome genes X chromosomes are inactivated randomly and stay inactivated Female mammals are mosaics

21. Nondisjuction

22. Nondisjuction

23. Polyploidies (e.g., in plants) are actually less serious than one too many (or one too few) autosomes (is a duplicate of all chromosomes) • Most abnormalities in numbers of autosomes, anueploidies(one too many or too few chromosomes), are very serious or fatal due to gene dosage imbalances • The fewer genes unbalanced, the less serious the condition; a trisomy is one extra chromosome • Down’s syndrome: Caused by a trisomy of chromosome number 21 (1 in 700 births)—mental retardation, mongoloid features, and heart defects • Most abnormalities of sex chromosomes do not affect survival • Klinefelter syndrome: Males with an extra X chromosome (XXY) (1 in 1000 male births) • Turner syndrome: Females missing one X chromosome (XO) (1 in 2500 female births) Common Aneuploidies

24. Down Syndrome Remember this Remember this

25. XO – Turner Syndrome Remember this An example of a monosomy Remember this Turner Syndrome (XO), Incidence: 1 in 2500 female births

26. XXY – Klinefelter Syndrome Remember this Remember this Klinefelter Syndrome (XXY), Incidence: 1:1000 male births

27. XXY – Klinefelter Syndrome

28. XYY+ – “Super” Male

29. Chromosomal Rearrangements

30. Translocation Translocation   Translocations and deletions can result in surviving partial trisomies or monosomies (again, the more genes involved, the more severe the consequences) Found in patients with chronic myelogenous leukemia (CML)

31. Genomic Imprinting

32. Cytoplasmic Inheritance Also plastid mutation Maternally transmitted

33. The End