Transcript 6.1 Human Inheritance

6.1 Human Inheritance
Patterns of Human Inheritance
• Mendel studied traits that were controlled by
genes with one dominant allele and one
recessive allele.
• The inheritance of traits is rarely this simple.
• Some human traits are controlled by single
genes with two alleles, and others by single
genes with multiple alleles. Still other traits are
controlled by many genes that act together.
Single Genes With Two Alleles
• Free or attached earlobes
• A widow’s peak
• If both parents have heterozygous alleles,
the probability of the offspring having
that trait is 75%.
Single Genes with Multiple Alleles
• Multiple alleles : Some traits are
controlled by a single gene that has more
than two alleles – three or more forms of
a gene that code for a single trait
• Ex. Blood type : A, B, AB, or O
• A, B are codominant. Type O is recessive.
Caucasians
African
American
Hispanic
Asian
O+
37%
47%
53%
39%
O-
8%
4%
4%
1%
A+
33%
24%
29%
27%
A-
7%
2%
2%
0.5%
B+
9%
18%
9%
25%
B-
2%
1%
1%
0.4%
AB +
3%
4%
2%
7%
AB -
1%
0.3%
0.2%
0.1%
Traits controlled by Many Genes
• Some human traits show a large number
of phenotypes because the traits are
controlled by many genes.
• The genes act together as a group to
produce a single trait.
• At least 4 genes control height in
humans.
• Skin, eye, and hair color are other traits
that are controlled by multiple genes.
The Sex Chromosomes
• The sex chromosomes are one of the 23
pairs of chromosomes in each body cell.
• The sex chromosomes carry genes that
determine whether a person is male or
female. They also carry genes that
determine other traits.
The Sex Chromosomes
• Girl or Boy?
– The sex chromosomes are the only chromosome
pairs that do not always match
– Girls : XX match
– Boys : XY do not match
• Sex Chromosomes and Fertilization
– Mother : XX,
Father XY
– 4 possibilities : XX, XX, XY, and XY
– 50% chance of a girl and 50% chance of a boy.
Sex Linked Genes
• Genes on the X and Y chromosomes are
often called sex-linked genes because
their alleles are passed from parent to
child on a sex chromosome.
• These traits are called the sex-linked
traits.
• EX: Colorblindness
Can you see the number in the
circle?
What shape do you see here?
Inheritance of Colorblindness
• Colorblindness is a trait controlled by a
recessive allele on the X chromosome.
• Carrier: a person who has one recessive
allele for a trait and one dominant allele.
• Higher chance for boys to receive the
colorblind gene than girls.
Can you recognize what it says here?
Previous slide : “NO”
• What bothers colorblind people most?
- When grilling a piece of meat, a red deficient
individual cannot tell whether it is raw or well
done. Many cannot tell the difference between
green and ripe tomatoes or between ketchup
and chocolate syrup! Many others are always
buying and biting into unripe bananas - they
cannot tell if they are yellow or green, and the
matt, natural material makes it even harder to
distinguish.
- Some food may look definitely disgusting to
color vision deficient individuals: a plate full of
spinach, for instance, just appears to them like
cow pat.
- They can however distinguish some citrus fruits. Oranges
seem to be of a brighter yellow than that of lemons.
- A colorblind person is generally unable to interpret the
chemical testing kits for swimming pool water, test strips for
hard water, soil or water pH tests because they rely on subtle
color differences.
- Many colorblind people cannot tell whether a woman is
wearing lipstick or not. More difficult to handle for some is the
inability to make the difference between a blue-eyed blonde
and a green-eyed redhead.
- Color vision deficiencies bother affected children from the
earliest years. At school, coloring can become a difficulty
when one has to take the blue crayon - and not the pink one to color the ocean.
- Bi-color and tri-color LEDs (Light Emitting Diodes): is that
glowing indicator light red, yellow, or green? Same problem
with the traffic lights...
The Effect of Environment
• Many of an organism’s characteristics are
determined by an interaction between
genes and the environment.
• People’s heights are controlled by several
genes, but also controlled by the diet.
• A good muscle coordination might help
you to play a musical instrument, but you
still have to practice.