1. Question of the Day 5-17 What are chromosomes composed of?
Where do we find chromosomes?
Objectives:
Discuss sex-linked traits

2. Unit # 9 Chromosomes and Inheritance
Book Chapter 12
My.hrw.com

3. Morgan’s Experiments For fruit flies red eyes = normal
Morgan found a male with white eyes
white eyed male X red eyed female  all F1 were red eyed … so red = dominant
F1 X F1  3 red eyed to 1 white eyed BUT all white eyed flies were males – EXPLAIN!

4. Xr Y XR XR Xr XR Y XR XR Xr XR Y
Original cross: white eyed male X red eyed female Xr Y XR XR Xr XR Y XR XR Xr XR Y

5. F1 X F1 XR Y XR XR XR XR Y Xr Xr XR Xr Y

6. Review:
Sex chromosomes – X and Y – chromosomes that contain genes that determine sex (along with other traits)
Autosomes – all other chromosomes and the genes they carry

7. Sex-linked traits –
traits that are coded by an allele on a sex chromosome
Why are there more X sex linked traits?
X chromosome is bigger than the y chromosome

8. Assignments
5-16
Previewing Assignment: Read 12.1 and answer #s 1-3, 6-9 on the bottom of page 240 – DUE Wednesday 5-18

9. Linked genes – genes that tend to be inherited together
Usually means they are on the same chromosome

10. XR Y Xr Xr XR Xr Y Xr Xr XR Xr Y
Question of the Day
5-11
Using what you learned yesterday about eye color for fruit flies cross a white-eyed female with a red eyed male and determine the geno and phenotypic ratios.
50% red eyed females XrXR and 50% white eyed males XrY XR Y Xr Xr XR Xr Y Xr Xr XR Xr Y

11. Mutations
Germ-cell mutation – mutations in organisms gametes – do not affect the organism itself but can affect its offspring
Somatic cells – organism’s body cells
Somatic-cell mutation – mutations that occur in organism’s body cells
Lethal Mutations – mutations causing death (mostly before birth) – Some mutations beneficial  leads to natural selection

12. Mutations
Chromosomal mutations = mutations involving changes in chromosome structure or number
Deletion – loss of a piece of a chromosome (it breaks off)
Inversion – chromosome part breaks off and reattaches backwards
Translocation – piece of chromosome breaks off and reattaches to a non-homologous chromosome

13. Mutations
Nondisjunction – chromosomes failing to separate during meiosis
Get too many, or too few chromosomes (Trisomy 21 = Down syndrome)
Review trisomy and monosomy
aneuploidy – having an abnormal number of chromsomes

14. Mutations

15. Gene mutations = changes in the DNA sequence that makes up a gene
Point Mutation –
substitution, addition or removal of a single nucleotide in DNA
Substitution –
when one nucleotide replaces another

16. Mutations Substitution – when one nucleotide replaces another
Insertion Mutation –
one or more nucleotide are added to a gene (can lead to a frame-shift mutation)
Frame-shift Mutation –
Deletion or addition of a nucleotide(s), shifting all the codons, changing all the amino acids

17. Mutations

18. Pedigrees
Pedigree – diagram that shows how a trait is inherited over several generations

19. Xr Y XR Y XR XR XR Xr F1 X F1 Original cross:
white eyed male X red eyed female
F1 X F1 Xr Y XR Y XR XR XR Xr