Human inheritance is complex, with some traits controlled by single genes with two alleles, others by single genes with multiple alleles, and many traits influenced by multiple interacting genes. Additionally, sex is determined by sex chromosomes, with females typically having two X chromosomes and males having one X and one Y chromosome. The probability of passing on traits is influenced by factors like whether alleles are dominant or recessive, and both genes and the environment interact to impact characteristics.

1. HUMAN INHERITANCE

2. HUMAN Inheritance
• When Mendel did his experiments, he
studied traits that were controlled by
one dominant allele and one recessive
allele.
• Unfortunately it is rarely that simple

3.  Some 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 acting
together.

4. Single Gene with Two alleles
 Onedominant and one recessive allele. The
dominant gene will be expressed if present:
Freckles and cleft chin
are also dominant.
Careful, this does not
mean more frequent!!!!!

5. What is the probability
 Ifthe parents were both heterozygous for
“widow’s peak”, what is the probability of
having a child without a “widow’s peak”?
Draw a Punnet square to explain your
answer.

6. Single genes with multiple
alleles
 Some human traits are controlled by a
single gene that has more than two alleles.
 Even though a gene may have multiple
alleles, a person can only carry two of those
alleles.
 Human blood type is controlled by a gene
with multiple alleles

7. Traits controlled by many
genes
 Traits like height, skin, eye and hair color,
as well as most other traits are controlled by
multiple genes that have several alleles.
This is what gives us such variety.

8. Sex Chromosomes
 Thesex chromosomes carry genes that
determine whether a person is male or
female. They also carry genes that
determine other traits.

9. Boy or Girl?
 Sex chromosomes are the only chromosome
pair that do not always match.
 If you are a girl, you have two X
chromosomes. (XX)
 If you are a boy, you have an X
chromosome and a Y chromosome. (XY)

10. Sex Chromosomes and
Fertilization
 Usea Punnet square to determine the
probability of having a boy or a girl.

11. Sex-Linked Genes
 Genes for some human traits are carried on
the sex chromosomes.
A person that has a recessive allele for a sex
linked trait and a dominant allele is called a
carrier. The carrier will not have the trait
but can pass it along to her offspring.

12. Genes and the environment
 Many of an organisms characteristics are
determined by an interaction between genes
and the environment.
 For example, your parents may be tall, but
if you do not get enough nutrition, you will
be shorter than them.