Transcript Human Genetics - Chapter 6

Human Genetics
Concepts and Applications
Tenth Edition
RICKI LEWIS
6
Matters of Sex
PowerPoint® Lecture Outlines
Prepared by Johnny El-Rady, University of South Florida
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Our Sexual Selves
Maleness or femaleness is determined at
conception
Another level of sexual identity comes from
the control that hormones exert on
development
Finally, both psychological and sociological
components influence sexual feelings
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Sexual Development
During the fifth week of prenatal development, all
embryos develop two sets of:
- Unspecialized (indifferent) gonads
- Reproductive ducts – Müllerian (female-specific)
and Wolffian (male-specific)
An embryo develops as a male or female based on
the absence or presence of the Y chromosome
- Specifically the SRY gene (sex-determining
region of the Y chromosome)
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Sex Chromosomes Determine Gender
Human males are the heterogametic sex
with different sex chromosomes, (XY)
Human females are the homogametic sex
(XX)
In other species sex can be determined in
many ways
- For example, in birds and snakes, males are
homogametic (ZZ), while females are
heterogametic (ZW)
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X and Y Chromosomes
X chromosome
- Contains > 1,500 genes
- Larger than the Y chromosome
- Acts as a homolog to Y in
males
Y chromosome
- Contains 231 genes
- Many DNA segments are
palindromes and may
destabilize DNA
Figure 6.1
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Table 6.1
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Sex Determination in Humans
Figure 6.4
Figure 6.6
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Y-linked Traits
Genes on the Y chromosome are said to
be Y-linked
Y-linked traits are very rare
Transmitted from male to male
No affected females
Currently, identified Y-linked traits involve
infertility and are not transmitted
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X-linked Traits
Possible genotypes
X+X+  Homozyogus wild-type female
X+Xm  Heterozygous female carrier
XmXm  Homozygous mutant female
X+Y  Hemizygous wild-type male
XmY Hemizygous mutant male
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X-linked Recessive Inheritance
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X-linked Recessive Traits
Examples:
- Ichthyosis = Deficiency of an enzyme
that removes cholesterol from skin
- Color-blindness = Inability to see red
and green colors
- Hemophilia = Disorder of blood-clotting
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X-linked Dominant Inheritance
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X-linked Dominant Traits
Congenital
generalized
hypertrichosis
Figure 6.8
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Solving Genetic Problems
Steps to follow:
1) Look at the inheritance pattern
2) Draw a pedigree
3) List genotypes and phenotypes and their
probabilities
4) Assign genotypes and phenotypes
5) Determine how alleles separate into gametes
6) Use Punnett square to determine ratios
7) Repeat for next generation
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