1. Chromosomes, Genes, Alleles and Mutations

2. What is a chromosome?

3. What is a gene?
A section of DNA that codes for a polypeptide

4. Allele
A version of a gene. Trait = tongue rolling Allele= roller or non roller

5. genome
All your genes!

6. Humans have 23 pairs of homologous chromosomes

7. Mutations

8. Mutations Changes to DNA are called mutations TACGCACATTTACGTACG
change the DNA
changes the mRNA
may change protein
may change trait
DNA
TACGCACATTTACGTACG
mRNA
AUGCGUGUAAAUGCAUGC aa
protein
trait

9. What Causes Mutations? Mistakes when DNA is copied
Inherited mutations (only occur when the mutation was in the gametes (sperm or egg)
Environmental factors:
Mutagens
Chemical: Pesticides, chemicals in cigarette smoke
Physical: x-rays, uv rays from the sun

10. Are Mutations Helpful or Harmful?
Mutations happen regularly
Almost all mutations are neutral
Many mutations are repaired by enzymes

11. Are Mutations Helpful or Harmful?
Some type of skin cancers and leukemia result from somatic mutations
Some mutations may improve an organism’s survival (beneficial)

12. Types of Mutations

13. Gene Mutation Animation

14. Gene Mutations Change in the nucleotide sequence of a gene
May only involve a single nucleotide
May be due to copying errors, chemicals, viruses, etc.

15. Types of Gene Mutations
Point Mutations
Substitutions
Insertions
Deletions
Cause a frame shift

16. Point Mutation Change of a single nucleotide
Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

17. Point Mutation
Sickle Cell disease is the result of one nucleotide substitution
Occurs in the hemoglobin gene

18. Frameshift Mutation Inserting or deleting one or more nucleotides
Changes the “reading frame” like changing a sentence
Proteins built incorrectly

19. Frameshift Mutation Original: The fat cat ate the wee rat.
Frame Shift (“a” added):
The fat aca tat eth ewe era t.

20. Amino Acid Sequence Changed

21. Gene Mutation Animation

22. HHMI sickle cell video

23. Describe the relationship between the following terms…
Gene, Allele, Chromosome, Genome and DNA

24. Explain how sickle cell anemia came about as a result of a mutation and relate that to the process of transcription and translation.
Explain why the sickle cell mutation is so common in populations of African decent.

25. Meiosis Overview
Major Understandings • One diploid nucleus divides by meiosis to produce four haploid nuclei. • The halving of the chromosome number allows a sexual life cycle with fusion of gametes. • DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids. • The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. • Orientation of pairs of homologous chromosomes prior to separation is random. • Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number. • Crossing over and random orientation promotes genetic variation. • Fusion of gametes from different parents promotes genetic variation

26. Chromosome Mutations May Involve:
Changing the structure of a chromosome
The loss or gain of part of a chromosome

27. Chromosome Mutations Five types exist: Deletion Inversion
Translocation
Nondisjunction
Duplication

28. Chromosome Mutation Animation

29. Deletion
Due to breakage
A piece of a chromosome is lost

30. Inversion Chromosome segment breaks off Segment flips around backwards
Segment reattaches

31. Duplication
Occurs when a gene sequence is repeated

32. Translocation Involves two chromosomes that aren’t homologous
Part of one chromosome is transferred to another chromosomes

33. Translocation

34. Nondisjunction Failure of chromosomes to separate during meiosis
Causes gamete to have too many or too few chromosomes
Disorders:
Down Syndrome – three 21st chromosomes
Turner Syndrome – single X chromosome
Klinefelter’s Syndrome – XXY chromosomes

36. Chromosome Mutation Animation

38. KARYOTYPE ANALYSIS

39. Chromosome Mutations Down Syndrome
Chromosome 21 does not separate correctly.
They have 47 chromosomes in stead of 46.
Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

40. Chromosome Mutations Cri-du-chat
Deletion of material on 5th chromosome
Characterized by the cat-like cry made by cri-du-chat babies
Varied levels of metal handicaps

41. Sex Chromosome Abnormalities
Klinefelter’s Syndrome
XXY, XXYY, XXXY
Male
Sterility
Small testicles
Breast enlargement

42. Sex Chromosome Abnormalities
XYY Syndrome
Normal male traits
Often tall and thin
Associated with antisocial and behavioral problems*

43. Sex Chromosome Mutations
Turner’s Syndrome X
Female
sex organs don't mature at adolescence
sterility
short stature

44. Sex Chromosome Mutations
XXX
Trisomy X
Female
Little or no visible differences
tall stature
learning disabilities
limited fertility

45. Normal Male
2n = 46

46. Normal Female
2n = 46

47. Male, Trisomy 21 (Down’s)
2n = 47