Chromosomes and Inheritance
Autosomes vs. sex chromosomes
Autosomes = the pairs of chromosomes
that are the same in males and females
In humans, these are chromosomes
# 1 - # 22
sex chromosomes = differ between males
and females of a species:
differ physically and in the genes
they carry
In humans, chromosome
# 23
sex determination in humans:
female gives:
x
&
male gives:
x
female
xx
male
x
&
y
xy
Alleles
alleles are different forms of a given gene
ex. gene = tongue rolling
tongue roller vs. non-roller
chromosome # 14
tongue
rolling gene
from mom
tongue
rolling gene
from dad
the alleles from mom and dad may
be the same, may be different
Each person carries 2 copies of each gene
(on their autosomes)
Genotype = the gene forms, or alleles
someone carries
Genotypes
RR- if they carry the same allele on
both chromosomes ->
HOMOZYGOUS
Rr- if they carry different alleles ->
HETEROZYGOUS
Phenotype = the physical or physiological
expression of those alleles
alleles can have different relationships
to each other
1.
dominant --- recessive
a dominant allele, when found in the
heterozygous condition, overrides the
recessive allele
Rr -> will result in a tongue roller
GENOTYPE
PHENOTYPE
RR = homozygous dominant
roller
Rr = heterozygous
roller
rr = homozygous recessive
non-roller
2. incomplete dominance
3. multiple alleles with codominance
ex. blood type
Genetic Disorders
1. genetic abnormality-
an uncommon version of a trait
ex. a person born
with 6 fingers
2. genetic disorder-
an inherited condition that will
result in mild to severe
health problems.
ex. cystic fibrosis
3. syndromea set of symptoms that characterize
a given disorder
Autosomal dominant inheritance =
trait will typically appear in every generation
HH or Hh
Ex. Huntington’s disorder (nervous system)typically fatal in 40’s or 50’s
Why does gene stay in population?
its effects occur post-reproduction
Autosomal recessive inheritancetrait (disorder) shows up less often in the population
because the trait can be masked by the dominant allele
Ex. galactosemia: gg
lactose
galactose
glucose
X
glucose-1-phosphate
results in a buildup of galactose in blood…
damage to eyes, liver, brain
x-linked recessive traitsgene is only found on the x chromosome- not the Y!
xAxA
xAy
xAxa
x ay
x ax a
33.3%
female
50%
male
Hemophilia in Royal Families in Europe
I-1 = King George III
III-1 and III-2 = Prince Albert and Queen Victoria
IV-5 and IV-6 = Alice of Hesse and Ludwig IV of Hesse
V-13 and V-14 = Alix and Nicholas II (Tsar of Russia)
VI-16 = Alexei
VIII-1 = Prince Charles
Changes in Chromosome Number
aneuploidy= the condition of having less than or
more than the normal diploid number of chromosomes
polyploidy- condition of having 3 or more entire sets
of chromosomes (lethal in humans)
Down syndrome (trisomy 21): The result of an extra copy of chromosome 21.
Down syndrome affects 1:700 children and alters the child's phenotype either moderately or severely.
cause of aneuploidy =
NONDISJUNCTION
Failure of paired chromosomes to disjoin (separate)
during cell division so that both chromosomes go to one daughter cell
and none to the other.
Patau syndrome (trisomy 13): serious eye, brain, circulatory defects as well as cleft palate.
1:5000 live births. Children rarely live more than a few months.