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SEX-LINKED GENES3/11/19

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DO NOW ‣ What is the difference between autosomes

and sex chromosomes?

‣ What is the similarity between autosomes and sex chromosomes?

‣ Turn in PUNNETT SQUARES sheets into the black basket

AGENDA▸ Introduction to Sex-linked genes

▸ Sex-linked Punnett Squares

TEXTBOOK▸ BRING YOUR TEXTBOOK TOMORROW!!!

HW

SEX-LINKED GENESCORNELL NOTES TITLE (PAGE 123 & 125)

CHROMOSOMES REVIEW• Which chromosomes are autosomes?

CHROMOSOMES REVIEW• Which chromosomes are sex

chromosomes?

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CHROMOSOME REVIEW▸ Autosomes: Chromosomes #1-22

▸ Sex-chromosomes: Chromosome #23, X/Y

INQUIRY▸ 2 questions

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WHAT DO YOU SEE?

INQUIRY▸Write two questions about what just

happened in the class:

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POSSIBLE QUESTIONS• Why were some students not able to

see the numbers?

• Is this genetically inherited?

COLOR BLINDNESS PEDIGREE: WHAT PATTERNS DO YOU SEE?

COLORBLINDNESS• Affects one in 10 males in US

• One in 100 in females in US

• Red-green colorblindness is most common

SEX-LINKED GENES▸ Genes found specifically in the sex

chromosomes (X and Y)

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THINGS TO NOTE• X-chromosome

• There are more than 100 sex-linked disorders mapped to the X-chromosome

• Y-chromosome

• Only contains a few genes

SOME SEX-LINKED TRAITS

• Colorblindness

• Hemophilia

• Male pattern baldness

• Duchenne Muscular Dystrophy

IS THE GENE IN THE Y OR X CHROMOSOME?

• Give 3 pieces of evidence to prove that the gene is in the Y or X chromosome

ANSWER: COLOR BLINDNESS IS IN THE X CHROMOSOME

WHEN ARE DOMINANT ALLELES EXPRESSED?▸When there’s at least ONE copy of a

dominant allele in the genotype

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WHEN ARE RECESSIVE ALLELES EXPRESSED?▸ In the absence of dominant alleles

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DOMINANT SEX-LINKED GENES▸ Dominant alleles will be expressed whether

there are 1 or 2 alleles

▸ XA Xa

▸ XA XA

▸ XA Y

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RECESSIVE SEX-LINKED GENES - FEMALES▸ For a recessive trait to be expressed in

females, two recessive alleles are needed (one in each X chromosome)

▸ Xa Xa

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RECESSIVE SEX-LINKED GENES - MALES▸ For a recessive trait to be expressed in males,

only one allele in the X chromosome is needed

▸ Xa Y

SEX-LINKED GENES NOTATIONS▸ A = Normal, a = condition

▸ XA Xa

▸ XA XA

▸ XA Y

▸ Xa Y

▸ Xa Xa

What extra information does this notation give

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SEX-LINKED PUNNET SQUARES▸ A = normal, a = colorblind

▸ XA Xa and Xa Y

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EXAMPLE 1▸ A = normal, a = colorblind

▸ XA XA and Xa Y

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EXAMPLE 2▸Mom is a carrier and dad is colorblind

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WHY ARE MALES MORE LIKELY TO HAVE A SEX-LINKED DISORDER THAN FEMALES?

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ILLUSTRATIVE SUMMARY▸ ALL terms

▸ At least 4 colors

▸ Label as necessary

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TEXTBOOK▸ BRING YOUR TEXTBOOK TOMORROW!!!

HW