Transcript Document

Essential question:
Why are there more
colorblind boys than
colorblind girls?

What is human inheritance?

How are characteristics affected by
human inheritance?

What is an example of a sex-linked trait
inheritance?
Notes:
Human Inheritance

Humans have 46 chromosomes
(23 pairs).

The 23rd pair of chromosomes are called
the sex chromosomes, and determines if
the individual is a male or female.
Notes:
Human Inheritance

Humans have 46 chromosomes
(23 pairs).

The 23rd pair of chromosomes are called
the sex chromosomes, and determines if
the individual is a male or female.

Use a punnett square to find the
probability that a couple will have a son.

What is the probability that the same
couple will have a daughter?

Some characteristics, like colorblindness
and albinism, are controlled by the genes
on the sex chromosomes.

Some characteristics, like colorblindness
and albinism, are controlled by the genes
on the sex chromosomes.
Colorblindness trait
X = allele with “normal” vision
Xc = allele with colorblind vision
X X = female with “normal” vision
Xc Xc = female with colorblind vision
X Y = male with “normal” vision
Colorblindness trait
X Xc
Since ‘normal’ vision is dominant, a
female with one X chromosome and
one Xc chromosome will have ‘normal’
vision.
She is, however, a carrier for the
colorblindness trait and can pass it on
to her children.
Colorblindness trait
Xc Y
Because there is not a second “normal” X
chromosome to dominate the
recessive trait, males with only one Xc
chromosome will be colorblind!