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GENES AND CHROMOSOMES
The Chromosome Theory of Heredity
1. Traits are determined by pairs of genes
(alleles)
2. A pair of genes are located on a pair of
chromosomes, one gene for each trait on each
chromosome of a pair.
3. In meiosis, the chromosomes and therefore
the genes, segregate independently – one of
each pair to a gamete
4. In fertilization, gametes unite resulting in a
fertilized egg that has two genes for each trait
carried on pairs of chromosomes.
SEX DETERMINATION AND
CHROMOSOMES
A. XX-XY CONDITIONS
IN DROSOPHILA: 2n= 8
P:
(6 + XX) ♀
Autosomes
(somatic chr)
(6+ XY) ♂
meiosis
Gonosomes
(sex chr)
G: ( 3+ X); (3+X)
(3+X) (3+Y)
Homogametes
Heterogametes
6 + XO
♂
6 + XXY
♀
6 + YO
zygote dies
IN HUMANS: 2n= 46
P: (44 + XX) ♀
(44+ XY) ♂
G: ( 22+ X); (22+X)
(22+X) (22+Y)
Homogametes
Heterogametes
44 + XO ♀ (TURNER SYNDROME)
44 + XXY ♂ (KLINEFELTER SYNDROME)
44 + YO
ZYGOTE DIES
44 + XXX
SUPER FEMALE
44 + XYY
POSIBLE SERIAL KILLER*
(TURNER SYNDROME)
(KLINEFELTER SYNDROME)
SUPER FEMALE
B. ZZ-ZW CONDITION
IN CHICKENS: 2n= 18
P: (16 + ZW) ♀
G: ( 8+Z); (8+W)
Heterogametes
(16 + ZZ) ♂
(8+Z) (8+Z)
Homogametes
C. XX-X0 CONDITION
IN GRASSHOPPER: 2n= 24
P: (22 + XX) ♀
(22 + X0) ♂
G: (11+X); (11+X)
(11+X); (11+0)
Homogametes
Heterogametes
D. HAPLOID –DIPLOID CONDITION
IN HONEYBEES:
P: (QUEEN) ♀ 2n= 24
(DRONE) ♂ n= 12
meiosis
G:
n
n
n
mitosis
n
eggs
n
n
sperm
fertilization
parthenogenesis
Male larvae (n)
DRONES
Female larvae (2n)
QUEEN
WORKERS
Differentiaton
due to
difference in
diet
In some species of animals, sex is determined by
environmental conditions or by the presence or
absence of the opposite sex
Bonellia, If there is more of
female individuals in the
population, the larva develops
into male, which is very small
and lives as a parasites in the
reproductive system of the
female.
In amphibians sex
determination is affected by
temperature of the
environment, and also by
hormones.
In certain annelids, when the number of
segments of the organism is small, it is a male.
When the number of segments increase, the
organism becomes female.
COLOR BLIND PEDIGREE MAP
dominant inheritance
recessive inheritance
1. Determine if the trait recorded in
the pedigree below is dominant or
recessive and sex-linked or not. Which
of the lettered individuals carry an
allele for the trait.
a
b
c
e
f
d
2. Determine if the trait recorded in the pedigree below
is dominant or recessive. Is it sex-linked or not?
a
b
c
d
e
3. Below is a pedigree for four generations of a family,
some of whose members exhibit a particular trait. From
the information in the pedigree, determine if the trait is
dominant or recessive, and sex –linked or not sex-linked.
Which of the lettered individuals is a carrier- that is,
heterozygous-for the trait?
a
b
c
d
4. Determine if the trait recorded in the
pedigree below is dominant or recessive and
sex-linked or not. Which of the lettered
individuals are heterozygous for the trait?
a
b
c
d
f
e
5. The pedigree below shows the blood types of
some individuals. List all the possible genotypes of
each lettered individuals.
O
a
O
b
A
B
f
A
c
O
A
B
AB
e
B
O
d