day17 sex-linked genes - waibiology.weebly.com · page 122 do now ‣ what is the difference...
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SEX-LINKED GENES3/11/19
PAGE 122
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