Transcript Hereditary Traits and Pedigrees

Pedigree Charts
• Pedigree charts allow us to work out:
– Which traits are recessive and which are dominant
– The genotypes of individuals
• we can see the phenotype, e.g. whether someone can
roll their tongue or not, but not always the underlying
genotype.
– E.g. Tongue rolling is a dominant gene
• The tongue rolling phenotype has two possible
genotypes- RR and Rr
• There non-rolling phenotype has only one possible
genotype- rr.
• Where do we need to dig deeper to find the genotype?
Tongue Rolling in one family
1
2
rr
RR/ Rr
7
3
4
8
5
9
6
rr
Rr
Rr
rr
Rr
RR/ Rr
Rr
10
RR/Rr
Male
11
12
16
Rr
rr
RR/ Rr
13
14
15
rr
Rr
Rr
17
RR/ Rr
18
?
Tongue
roller
Nonroller
Female
Sex-linked traits
• The chromosomes which determine sex
are of uneven length.
• The X chromosome contains many more
genes than the Y chromosome. These
chromosomes code for sex but also for
other characteristics
• For a female child (XX), genetic
inheritance from this chromosome
follows a normal pattern- one allele
from mother and one from father.
• For a male child (XY) the genetic
inheritance is different. Here there are
many genes only encoded on the X
chromosome, so the male child will
inherit the mother’s gene, with none
from the male.
• About 50 known diseases are inherited
this way (eg. Haemophaelia)
Haemophaelia
• Haemophaelia is carried only on the X gene, and it is
recessive
• For a female child, an X will be inherited from mother and an
X from father. Even if one chromosome carries the gene for
haemophaelia, it will be overridden by normal blood clotting
gene from the other parent (genotype XHXh).
• As a result it is unlikely for a female to suffer from
haemophaelia, but she can carry the disease
• For a male child, and X will be inherited from the mother and
Y from the father. The Y does not have a gene coding for
blood clotting, so the male child takes on the gene of the
mother. A male with haemophaelia has genotype XhY
• If the mother is a carrier, XHXh, what is the chance of her son
having haemophaelia?
• If a female was a haemophaelia sufferer, what would the
genotypes of her parents be?