Inheritance Patterns

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Inheritance Patterns Human Genetics

• Chapter 12

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Sex Chromosomes Autosomes

• Sex chromosomes contain genes that determine
  gender (1 pair)
• XX female
• XY male
• Autosomes-remaining chromosomes, not directly
  involved with determining gender (22 pair)

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Sex Determination

• In male mammals, the Y chromosome has a SRY gene
• Sex-Determining Region Y
• This gene makes a protein that causes the gonads
  of an embryo to develop as testes
• Because females do not have this gene the gonads
  develop as ovaries

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Sex-Linked Traits

• Are determined by genes located on the X or Y
  chromosomes
• N normal n disease

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Sex linked traits in females

• XNXN normal
• XNXn normal (carrierhave the
• normal phenotype, but carry the
• bad gene, it could be given to
  
• their offspring)
• XnXn diseased

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Sex linked traits in females cont

• Recessive sex linked traits rarely appear in
  females because they will probably have a
  dominant allele to mask the recessive one
• They get two chances since they have two Xs

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Sex linked traits in males

• XNY normal
• XnY diseased
• No carriers in males for sex linked traits

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Sex linked traits in males cont

• Since males only have one X chromosome, recessive
  genes on that chromosome are always expressed
• They dont get the chance to be a carrier, they
  either have it, or dont

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Sex Linked Diseases

• Colorblindness
• Recessive, on X chromosome
• Cannot tell difference between certain colors
• N normal and n colorblind

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Sex Linked Diseases

• Hemophilia
• Recessive, on X chromosome
• Cannot produce a clotting factor for blood, could
  bleed to death from a small wound
• H normal and h hemophilia

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A female carrier marries a colorblind male. Give
g p ratio of offspring
G 1XN Xn 1Xn Xn 1XN Y 1Xn Y P 1 carrier
female, 1 colorblind female, 1normal male, 1
colorblind male
Y
Xn
XN Xn
XN Y
XN
Xn Xn
Xn Y
Xn
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What percentage of offspring will be colorblind?
50
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A colorblind female marries a normal male. What
can you tell me about her sons?
Y
XN
XN Xn
Xn Y
Xn
All of her sons will be colorblind
XN Xn
Xn Y
Xn
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Can a colorblind father make his son colorblind?

• No, the father gives his son a Y chromosome and
  the gene for colorblindness is located on the X
• A mother makes her son colorblind

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A man with hemophilia marries a woman who is
normal (not carrier). Give g p ratio of
children
Y
Xh
XH Xh
XH Y
XH
XH Xh
XH Y
XH
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G 2 XH Xh 2 XH Y P 2 carrier females 2
normal males