Describe the location of genes in chromosomes./Explain the different patterns of Non-Mendelian inheritance.

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Sex Determination
and
Sex Chromosomes

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Objectives:
• Discuss how sex is
determined

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In multicellular organisms, it is important
to distinguish between:
• primary sexual differentiation
•involves only the gonads where
gametes are produced
• secondary sexual differentiation
•involves the overall appearance of
the organism

10. Copyright © 2009 Pearson Education, Inc. Figure 7.2

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The Y Chromosome Determines
Maleness in Humans
• Human karyotype revealed that
one pair of chromosomes differs in
males and females:
• females have two X
chromosomes
• males have one X and one Y
chromosome

12. Copyright © 2009 Pearson Education, Inc. Figure 7.6
Normal Human Karyotypes

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• Persons with
Klinefelter
syndrome have:
• male genitalia
• more than one
X chromosome
(usually XXY, or
a 47,XXY
karyotype) http://all4freehere.com/2009/07/what-is-klinefelters-syndrome/

14. Copyright © 2009 Pearson Education, Inc. Figure 7.7a

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• Persons with
Turner syndrome
usually have:
• a single X
chromosome
• no Y
chromosome
(45,X karyotype)
• female genitalia
http://www.lucinafoundation.org/assets/turner-syndrome.jpg

16. Copyright © 2009 Pearson Education, Inc. Figure 7.7b

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• 47, XXX – Trisomy X
• 3 X chromosomes along with a
normal set of autosomes results in
female differentiation.
• Usually normal
• In other cases, underdeveloped
secondary sex characteristics,
sterility, and mental retardation may
occur.

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47, XYY –
Jacobs
Syndrome
• Males are
usually over 6
feet tall.
https://slideplayer.com/slide/16570608/

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• The Y
chromosome
contains far
fewer genes than
the X
chromosome.
http://blogs.discovermagazine.com/notrocketscience/files/2010/07/XY.jpg

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• Y chromosome
contains:
• the male-
specific region
of the Y (MSY)
• a sex-
determining
region of the Y
(SRY)
Section 7.3

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The Ratio of Males to Females
in Humans is not 1.0
• Primary sex ratio reflects the
proportion of males to females
conceived in a population.
• Secondary sex ratio reflects
the proportion of each sex that
is born.
http://partywarehouse.co.nz/zen/images

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Key concepts
• Males have 44 body chromosomes and
two sex chromosomes X and Y. The
males determine the sex of their
children. Females have 44 body
chromosomes and two sex
chromosomes, both X. The total number
in each cell of individual is 46. These
chromosomes contain the genes, which
are the factors of heredity.
http://partywarehouse.co.nz/zen/images