Transcript Gender-Linked Inheritance PPT

Bell-ringer 2/10
Complete on the back of today’s notes page.
You will get your comp books back on Monday or Tuesday.
All project grades should be in by the end of the day today.
In dogs, wirey hair (B) is dominant to smooth (b).
1. Cross a homozygous wire-haired dog with a smoothhaired dog.
2. What will be the phenotype of the F1 generation?
3. What will be the genotype of the F1 generation?
4. What will be the phenotypic ratio of the F2 generation
(if you cross two dogs from F1)?
GENDER DETERMINATION
• Humans have 23 pairs of chromosomes.
• There are 22 pairs of homologous chromosomes
called autosomes. Homologous autosomes look alike.
• The 23rd pair of chromosomes differs in males
and females.
GENDER DETERMINATION
• These two chromosomes, which determine the gender of an
individual, are called gender (or sex) chromosomes and are
indicated by the letters X and/or Y.
MALES
FEMALES
XY
XX
MALES
FEMALES
XY
XX
Y
X
X
X
• It is the male gamete that determines the
gender of the offspring.
(Take that, Henry VIII)
So if you are a boy….EVERYTHING on the X chromosome is
inherited ONLY from your mother’s side of the family.
If you are a girl….You inherit X-linked traits from both your mother
and your father.
X
Y
There are approx.
1100 traits that are
located on the X
chromosome
There are 78 traits
that are located on
the Y chromosome
Some Examples:
Some Examples:
● Sperm production (many genes)
● Hemophilia (blood clotting)/recessive
● Testes tissue production
● Color-blindness/recessive
● Tooth enamel development
● Amount of tooth enamel
● Certain types of brain development
● Certain types of invol. muscle control
● Muscular Dystrophy/recessive
● Light sensitivity in the eyes
Remember how we’ve talked about for every trait,
you have two alleles that make your genotypeone came from mom and one came from dad.
B
b
If you are a girl, this is the same…
You still have an allele from mom and from dad
Because you have two X chromosomes.
X
B
X
b
Boys, however, only have one X chromosome
And it does not share the same genes as the Y chromosome…so
therefore, they only have ONE ALLELE per X-linked trait.
B
X
Y
Gender-Linked Traits in Humans
Many human traits are determined by genes that are
carried on the gender chromosomes; most of these
genes are located on the X chromosome.
Recessive Gender-Linked Traits:
If a son receives an X chromosome with a recessive allele, the
recessive phenotype will automatically be expressed.
r
X Y
However, a female would have to have the recessive allele on
both of her X chromosomes for the recessive trait to be
expressed
r
X X
r
Gender-Linked Traits in Humans
Two traits that are governed by X-linked recessive
inheritance in humans are red-green color blindness
and hemophilia.
• People who have red-green
color blindness can’t
differentiate these two colors.
• Color blindness is caused by
the inheritance of a recessive
allele on the X chromosome.
Hemophilia: An X-linked disorder
• Hemophilia is an X-linked disorder that causes a
problem with blood clotting.
• About one male in every 10 000 has hemophilia, but
only about one in 100 million females inherits the
same disorder.
X Inactivation in females
• Random selection of X chromosome in somatic cells
Inactive throughout cell’s lifetime
Xa = active X chromosome
Xi = inactive X chromosome