Transcript 14.1_Human_Chromosomes

1 Review What are autosomes
Explain What determines whether a person is male
or female
Propose a Solution How can you use a karyotype to
identify a species
2 Review Explain how sex linked traits work
Infer Why would the Y chromosome be unlikely to
contain any of the genes that are absolutely
necessary for survival
CH 14 HUMAN HEREDITY
14.1 Human Chromosomes
Karyotypes

Shows the complete
diploid set of
chromosomes grouped
together in pairs, arranged
in order of decreasing size.

Genome
 Full
set of genetic information that an organism
carries.
Sex Chromosomes
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Two of the 46 chromosomes determine sex
Females are XX
Males XY.


X chromosome contains
1200 genes
Y chromosome contains
140 genes
 Most
are associated with
male development.
Autosomal Chromosomes

Remaining 44 human chromosomes.
Transmission of Human Traits

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Many traits have a pattern of simple dominance
Many are also codominant.
Dominant and Recessive Alleles

Rhesus, or Rh blood group
 Rh+

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and Rh-
Rh+ is dominant so heterozygous individual is Rh+
Rh- individuals need to have both negatives.
Codominant and Multiple Alleles
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Human blood types
 Determined
by a gene with three alleles: IA, IB, and i.
Codominant and Multiple Alleles

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Alleles IA and IB are codominant
Produce molecules known as antigens on the
surface of red blood cells
Individuals with alleles IA and IB produce both A
and B antigens
 Blood

type AB
The i allele is recessive
 Homozygous
are type O.
for the i allele (ii) produce no antigen and
Sex Linked Gene

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
Gene located on a sex chromosome
Genes on Y chromosomes only pass from father to
son
Genes on X chromosome are found in both sexes
 Remember
males only have one.
Sex-Linked Inheritance
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Three genes responsible for color vision all are on
the X chromosome
Males only have one X so if they have one
recessive allele they will have some form of color
blindness, 1 in 12
Females have 2 X chromosomes so they would
need both copies of a recessive allele, 1 in 200.
X-Chromosome Inactivation



Females really only need to use 1 X chromosome
(males make it work)
The second X chromosome is turned off
Barr Body
 Inactivated
side.
x chromosome that gets shoved off to the
X-Chromosome Inactivation
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
Also occurs in other mammals like cats
One X chromosome has an allele for
orange spots
Other X chromosome has an allele for
black spots
Some cells has one X chromosome
switched off other cells turns off the
other.
Pedigree

Shows the presence or absence of a trait according
to the relationships between parents, siblings, and
offspring.

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This pedigree shows how a white lock of hair just
above the forehead passes through three
generations of a family
White lock is dominant.

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Grandfather has trait
Two of his three children inherited the trait
Three grandchildren have the trait, but two do not.

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All family members lacking this trait must have
homozygous recessive alleles
One of the grandfather’s children lacks the white
forelock trait, so the grandfather must be
heterozygous.