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

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

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!

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

F1 X F1 XR Y XR XR XR XR Y Xr Xr XR Xr Y

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

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

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

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

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

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

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

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

Mutations

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

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

Mutations

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

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