1. What are chromosomes composed of?

2. Where do we find chromosomes?

• Objectives:

– Discuss sex-linked traits

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Unit # 9 Chromosomes Unit # 9 Chromosomes and Inheritanceand Inheritance

Book Chapter 12Book Chapter 12

My.hrw.comMy.hrw.com

Morgan’s ExperimentsMorgan’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 XRXr

XRXr

XRY

XRY

Original cross: white eyed male X red eyed female

XR Y

XR

Xr Xr XR

XRXR

Xr Y

XRY

F1 X F1

Review:Review:•Sex chromosomesSex chromosomes – X and Y – – X and Y – chromosomes chromosomes that contain genes that determine sexthat contain genes that determine sex (along (along with other traits)with other traits)•AutosomesAutosomes – – all other chromosomes and the all other chromosomes and the genes they carrygenes they carry

• Sex-linked traitsSex-linked traits – – traits that are traits that are

coded by an coded by an allele on a sex allele on a sex chromosomechromosome

– Why are there Why are there more X sex more X sex linked traits?linked traits?• X chromosome X chromosome

is bigger than is bigger than the y the y chromosomechromosome

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

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• Linked genesLinked genes – – genes that tend to be genes that tend to be inherited togetherinherited together

• Usually means they are on Usually means they are on the the same chromosome same chromosome

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.

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XR Y

Xr

Xr

XR

XRXr

Xr

Xr

Xr

YY

50% red eyed females XrXR and 50% white eyed males XrY

• Germ-cell mutationGerm-cell mutation – – mutations in mutations in organisms gametesorganisms gametes – do not affect the – do not affect the organism itself but can affect its organism itself but can affect its offspringoffspring

• Somatic cellsSomatic cells – organism’s – organism’s body cellsbody cells

• Somatic-cell mutationSomatic-cell mutation – mutations that – mutations that occur in organism’s occur in organism’s body cellsbody cells

• Lethal MutationsLethal Mutations – mutations causing – mutations causing death death (mostly before birth) – Some mutations (mostly before birth) – Some mutations beneficial beneficial leads to natural selectionleads to natural selection

Chromosomal mutations = mutations Chromosomal mutations = mutations involving changes ininvolving changes in chromosome chromosome structure or number structure or number

• DeletionDeletion – – loss of a piece of a loss of a piece of a chromosomechromosome (it breaks off) (it breaks off)

• InversionInversion – chromosome part breaks off – chromosome part breaks off and and reattaches backwardsreattaches backwards

• TranslocationTranslocation – piece of chromosome – piece of chromosome breaks off and breaks off and reattaches to a non-reattaches to a non-homologous chromosomehomologous chromosome

• NondisjunctionNondisjunction – – chromosomes failing chromosomes failing to separate during meiosisto separate during meiosis

• Get too many, or too few Get too many, or too few chromosomes (Trisomy 21 = Down chromosomes (Trisomy 21 = Down syndrome)syndrome)

–Review trisomy and monosomyReview trisomy and monosomy

• aneuploidy – aneuploidy – having an abnormal having an abnormal number of chromsomesnumber of chromsomes

• Point MutationPoint Mutation – – – substitution, addition or removal of a substitution, addition or removal of a

single nucleotidesingle nucleotide in DNA in DNA• SubstitutionSubstitution – –

– when one nucleotide replaces anotherwhen one nucleotide replaces another

Gene mutations = changes in the DNA Gene mutations = changes in the DNA sequence sequence that makes up a genethat makes up a gene

• SubstitutionSubstitution – – – when one nucleotide replaces anotherwhen one nucleotide replaces another

• Insertion MutationInsertion Mutation – – – one or more nucleotide are one or more nucleotide are added to a geneadded to a gene

(can lead to a frame-shift mutation)(can lead to a frame-shift mutation)• Frame-shift MutationFrame-shift Mutation – –

– Deletion or addition of a nucleotide(s), Deletion or addition of a nucleotide(s), shifting all the codonsshifting all the codons, changing all the , changing all the amino acidsamino acids

PedigreePedigree – diagram that – diagram that shows how a shows how a trait is trait is inherited inherited over several over several generationsgenerations

Xr YXR

XR

XR YXR

Xr

Original cross:

white eyed male X red eyed female F1 X F1