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S1-1-14 Explain the inheritance of sex-linked traits in humans and use a pedigree.
S1-1-08 Investigate adaptations of plant and animal species which enhance reproductive success.
Vocabulary & People Sex-linked PedigreeNatural Selection Adaptation
Sex chromosome X carries genes that code for traits other than gender.
Traits determined by genes on the X chromosome are called sex-linked traits.
Hemophilia, colour-blindness, and baldness are three common examples
• Inherits trait from mother (give the X)• Phenotype always shows gene (no other allele to mask it)
• Will pass to ALL daughters
xy
xx
• Inherited from either parent
• Needs two alleles to show recessive trait
• One recessive allele: will not show the trait - but is a “carrier”
Sex-linked traits are more common in males
Father = XY
Mother = XX
XYXX
X
X
X
X
Y
Y
X
X
½ disorder free – 50%
¼ color-blind male – 25%
¼ female carrier – 25%
Mother is a carrier
Pedigree: diagram representing the phenotype history of a family.
Symbols:Male – squareFemale – circle Dominant trait – blankRecessive trait – filled
Genotypes can be determined by analyzing the trends of the pedigree
A widow's peak hairline (W) is dominant over a straight hairline (w):
ww
W
ww ww ww
wwW W
W
W
WW
w
w
w w
w
?
?
What are the genotypes for each person in this family?
Natural selection is the gradual process of traits becoming more common in a
population because the traits may improve reproductive success of organisms in an
environment.
(It is a key mechanism of evolution)
Luck and timing has something to do with it too…
Anything that gives you an
advantage will help you pass
that positive trait on to offspring
disadvantage : no offspring
“Only The Strong Survive”
Adaptation: a naturally selected trait that enhances reproductive success.
How would big tail feathers make him more successful?
How would they make him less successful?
• Can be physical or behavioural
Examples of Adaptations
Behavioural • caring for young• mating calls• dances• fighting
Physical• colours / camouflage • size / shape• pheromones • multiple offspring
Those best able to modify their behavior or those with positive mutations that improve
their survival and reproductive success pass on these traits to future offspring
Think of adaptations that have evolved to help an organism (including humans)
survive its environment and reproduce.