Download Human Inheritance

Human Inheritance
Key Concepts
1. What are some patterns of
inheritance in humans?
2. What are the functions of the sex
chromosomes?
3. What is the relationship between
genes and the environment?
Key Terms
• Multiple alleles
• Sex chromosomes
• Sex-linked genes
• carrier
Patterns of Human Inheritance
• Human traits are controlled by:
– single genes with two alleles
–others by single genes with multiple
alleles.
–Still other traits are controlled by many
genes that act together
Single Gene with Two Alleles
• Have 1 dominant and 1 recessive allele
• Have 2 distinctly different phenotypes
• Ex. Widow’s Peak , dimples
Single Genes with Multiple Alleles
• Some traits have more than 2 alleles although
a person can have only 2 of those alleles
because chromosomes exist in pairs.
• Each chromosome in a pair carries only 1
allele for each gene
• Ex. Human blood type –
3 alleles A, B, O
A and B are codominant
O is recessive
Traits Controlled by Many Genes
• Produce a large variety of
phenotypes
• Genes act together as a group to
produce a single trait
• Ex. Height – at least 4 genes
– Skin color – at least 3 genes
The Sex Chromosomes
• One of the 23 pairs of chromosomes that
carries the genes that determine whether a
person is male or female
• Also carries genes that determine other traits
Girl or Boy?
• The only chromosome
pair that does not always
match
• Girl – two sex
chromosomes match (XX)
• Boy –don’t match, one is
an X other is a Y
(XY)
– The Y chromosome is
smaller than the X
Sex Chromosomes and Fertilization
• Egg cells all carry an X chromosome
• Sperm cells carry either an X or a Y
• When a sperm cell with an X chromosome
fertilizes an egg cell, the egg has 2 X’s = girl
• When a sperm cell with a Y chromosome
fertilizes an egg cell, X…….
result---------XY = Boy
Sex-linked Genes
• Genes for some human traits are carried
on the sex chromosomes
• Traits controlled by sex-linked genes are
called sex-linked traits
• EX. Red-green colorblindness
• Most of the genes on the X chromosome
are not on the Y chromosome
• An allele on the X may not have a match on
the Y
Sex-Linked Genes
• Sex-linked genes can have dominant and
recessive alleles
• In females a dominant allele on one X will
mask a recessive on the other X
• In males, there is no matching allele on
the Y to mask a recessive allele on the X
• Any trait on the X chromosome in males
(even a recessive trait) will produce the
trait in a male who inherits it.
Inheritance of Colorblindness
• Colorblindness is a trait controlled by a recessive
allele on the X chromosome
• Many more males have colorblindness than
females
• Females can be carriers. They have one dominant
trait for normal color vision and one recessive
trait for colorblindness. They have normal color
vision
• Males cannot be carriers. If a male inherits one
recessive allele – he will be colorblind.
Red-Green Colorblindness
Inheritance of Colorblindness
• If the mother passes on the X chromosomewith the allele for colorblindness to a son, he
will be colorblind- Males only have to inherit
one allele to be colorblind
• If the mother passes the X chromosome with the
colorblind allele onto a daughter, she will also
have an X chromosome from her father. If her
father has normal color vision, then she will
inherit the dominant allele for normal color vision
from him and she will have normal color visionbut she will be a carrier. Females need 2 to have
trait.
Test for Red Green Colorblindness
Inheritance of Colorblindness
Father XCY
XC
Y
XC
XCXC
XCY
XCXc
XcY
Mother
XCXc
Xc
The Effect of Environment
 Many of a person’s characteristics are
determined by an interaction between
genes and the environment
 Several genes work together to determine
height
 Environment affects height – a poor diet
can prevent a person from reaching their
potential
 Environmental factors can also affect
human skills – Ex. Playing a musical
instrument – need instruction to play well