Transcript Inheritance powerpoint #3 - Year 10 Life Science

Assessment Dates
Write these dates into your planner:
Genetics Test  Monday 2nd of March Period 1
Genetic Disorder Research Project 
Thursday 5th of March Period 4
Page 20 of your genetics booklet
1 topic per person, 1st in best dressed
You will have two periods to work on this in class
Sex-linked
Inheritance
1.3 – Characteristics and Inheritance Page 22
Sex linked Inheritance
Some genes are found on the X chromosome and not the
Y chromosome. These are called sex-linked genes
because they are present on one of the chromosomes
that are also responsible for the determination of gender
Sex linked Inheritance
As males have only one X chromosome they are more
commonly affected by X linked traits.
This is because they only need one copy of the allele to
express the trait.
Male = XY
Female = XX
Sex linked Inheritance
Carrier: someone who has one normal allele and one
abnormal allele for a trait (heterozygous). They do not
have the abnormal phenotype.
Sex linked  only females can be carriers XH Xh
Males can not be carriers as they do not have a letter on
the Y. They are either dominant or recessive
Please note when looking at sex-linked inheritance, we
include the X and Y chromosomes as well as the alleles
Haemophilia – Sex-Linked Recessive Disorder
Dominant Allele
Recessive Allele
Sex-Linked Recessive Disorder
H = normal (dominant)
h = haemophilia (recessive)
Hh = carrier (heterozygous)
Sex-Linked Recessive Disorder
Punnet Square
Punnet Square
What is the probability that they will have a haemophilia child?
Sex-linked Traits
Practice Problems
Genetic Booklet pages 11 - 15
Assessment Dates
Write these dates into your planner:
Genetics Test  Monday 2nd of March Period 1
Genetic Disorder Research Project 
Thursday 5th of March Period 4
Page 20 of your genetics booklet, Rubric on website
http://year10lifewithmisszammit.weebly.com/dna-and-genetics.html
1 topic per person, 1st in best dressed
You will have two periods to work on this in class
Pedigree Charts
You can look at a pedigree chart and determine whether
traits are dominant or recessive.
Pedigree Charts
You can also tell if they are sex-linked or autosomal
A sex linked recessive characteristic is determined by an allele
that is carried only on the X-chromosomes
Since there is only one X in a male genotype (XY), a male who
carries the recessive allele XaY will show the condition
A female who carries a recessive allele in one X chromosome
XAXa is a carrier (she can pass this onto her offspring)
A female who carries a recessive allele in both X chromosomes
XaXa will show the condition
Hints recognising the type of inheritance
1. Recessive inheritance: Affects both male and female
equally. Skips a generation
2. Dominance inheritance: Affects both males and
females equally. Occurs in every generation
3. Sex linked inheritance: Affects mainly males. Females
only can be carriers
Pedigree Charts
Pedigree Symbols
Female Carrier
Colour Blindness
The daughters are all carriers
because they have inherited the
colour-blindness allele from their
father. However their vision will be
normal.
The sons have normal vision
because they can only inherit the
X chromosome from their mother
which carries the dominant allele
Colour Blindness
Half the sons of a carrier
mother will have normal
vision. The other half will
be colour-blind.
All the daughters will
have normal vision but
half will be carriers of
the disease
Rudolph’s red nose pedigree
Reindeer with a shiny nose are a valued part of
Santa’s sleigh team.
Reindeer with bright shiny noses have the
recessive trait (n)
Reindeer with the traditional black nose have the
dominant trait (N).
Rudolph was the only fawn
of his parents. Donner,
Rudolph’s father, was
heterozygous for the trait of
his black nose. Charity,
Donner’s mother and
Rudolph’s grandmother,
had a luminescent red nose
that she hid with makeup.
Donner’s father Nicholas,
Rudolph’s grandfather, had
a black nose. His bloodline
was pure, making him
homozygous for his black
nose.
Rudolph’s mother, Mrs. Carol
Donner, also had a black
nose. Like her husband she
was heterozygous for her
black nose. Her parents, Mr.
and Mrs. Rockefeller, were
also heterozygous. Her two
younger brothers both had
black noses, but Klaus was
homozygous while Giftson
was heterozygous. Her
younger sister, Rose, luckily
was born with a red nose
since she was afraid of the
dark!
Donner and Mrs. Donner married
and gave birth to their famous son
Rudolph. Rudolph is famous for
having the recessive trait and
saving Christmas with his bright red
nose. What doesn’t get mentioned
in the story is that a few years later
Donner and Mrs. Donner gave
birth to another fawn, a girl named
Noel, who had the traditional
black nose. They weren’t sure if
she was homozygous or
heterozygous until she married a
reindeer from the South Pole, Boris,
who had a shiny red nose. They
gave birth to two fawns with shiny
red noses. Since they were girls
they named them Holly and Ivy.
As time passed Rudolph caught
the eye of a pretty reindeer
named Claudia. Claudia had a
traditional black nose, but she
had a few relatives with red
noses, so she assumed she was
carrier for the trait of a red nose.
Rudolph and Claudia went on
to have three fawns. The oldest
Gabriel and the youngest Yule
were born with the same
luminescent red nose as their
father and loved to play
flashlight tag with their noses
when they should have been
sleeping. But, the middle fawn, a
girl named Joy, had a plain
black nose.
Pedigree Chart
Practice Problems
Genetic Booklet pages 16-18