Transcript Chapter 6, Section 1: Human Inheritance

 Identify
some patterns of inheritance in
humans.
 Describe the function of the sex
chromosomes.
 Explain the relationship between genes and
the environment.
 Some
human traits are controlled by single
genes with two alleles, and others by single
genes with multiple alleles. Still others are
controlled by many genes that act
together.
 Several
human traits are controlled by a
single gene with one dominant allele and one
recessive allele.
 These traits have two distinctly different
phenotypes.
 This type of inheritance includes the
following traits: attached/free earlobes and
a widow’s peak.
 Some
human traits are controlled by a single
gene that has more than two alleles (called
multiple alleles).
 Multiple alleles is three or more forms of a
gene that code for a single trait.
 Even though a gene can have multiple
alleles, a person can only carry two of those
alleles because chromosomes exist in pairs.
Each chromosome in a pair only carries one
allele for each gene.
 Human
blood type is controlled by a gene
with multiple alleles:
 There
Blood type:
Combination
of Alleles:
A
IAIA or IAi
B
IBIB or IBi
AB
I AI B
O
ii
are four main blood types: A, B, AB,
and O. Three alleles control the inheritance
of blood types.
 The
allele for blood types A and B are
codominant.
 The alleles for blood type O is recessive.
 When two codominant alleles are inherited,
neither allele is masked, thus a person who
inherits both an A allele and a B allele, has
the AB blood type.
 Some
human traits show a large number of
phenotypes because the traits are controlled
by many genes.
 These genes act together as a group to
produce a single trait.
 At least four genes control height in humans,
so there are many possible combinations of
genes and alleles.
 Skin,
eye and hair color are other human
traits that are controlled by multiple alleles.
 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 are the only
chromosome pair that do not always match.
 If you are a girl, your sex chromosomes
match: XX.
 If you are boy, your sex chromosomes do not
match: XY.
 All
eggs carry one X chromosome because all
females have two X chromosomes.
 Each sperm has either an X or a Y
chromosome (but not both) because all
males have an X and a Y chromosome.
 Half of a male’s sperm will have an X
chromosome and half will have a Y
chromosome.
 If
a sperm with an X chromosome fertilizes
an egg, the baby will be a girl.
 If a sperm with a Y chromosome fertilizes an
egg, the baby will be a boy.
 The
genes for some traits are carried on the
sex chromosomes.
 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
chromosomes.
 Sex linked traits include red-green color
blindness. A person with this trait cannot
distinguish between red and green.
 Unlike
most chromosome pairs, the X and Y
chromosomes have different genes.
 Most of the genes on the X chromosome are
not on the Y chromosome, so an allele on an
X chromosome may not have a corresponding
allele on the Y chromosome.
 Like
other genes, sex-linked genes can have
dominant and recessive alleles.
 In females, a dominant allele on one X
chromosome will mask a recessive allele on
the other X-chromosome so the organism will
not be affected in her phenotype.
 In
males, there is no matching allele on the Y
chromosome to mask the allele on the X
chromosome, so as a result, any allele on the
X chromosome (even a recessive one) will
produce the trait in a male who inherits it.
 Males are much more likely than females to
have a sex-linked trait that is controlled by a
recessive allele
 Colorblindness
is a trait controlled by a
recessive allele on the X chromosome.
 Many more males than females have redgreen colorblindness because the female
would have to receive recessive alleles from
both mom and dad.
 Males only have to receive a recessive allele
from mom in order to be red-green
colorblind.
 Many
of an organism’s characteristics are
determined by an interaction between
genes and the environment.
 Genes are not the factors that influence
height.
 Someone’s diet can affect a person’s height.
 A diet lacking in protein, certain minerals, or
certain vitamins can prevent someone from
growing as tall as might be possible.