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) ♀ (6+ XY) ♂

G: ( 3+ X); (3+X) (3+X) (3+Y)

Homogametes Heterogametes

meiosisAutosomes

(somatic chr)Gonosomes

(sex chr)

6 + XO ♂

6 + XXY ♀

6 + YO zygote dies

P: (44 + XX) ♀ (44+ XY) ♂

G: ( 22+ X); (22+X) (22+X) (22+Y)

Homogametes Heterogametes

IN HUMANS: 2n= 46

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) ♀ (16 + ZZ) ♂

G: ( 8+Z); (8+W) (8+Z) (8+Z)

Heterogametes 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

G:

meiosis mitosis

eggs spermnn n n nn

parthenogenesis

fertilization

Male larvae (n) Female larvae (2n)

DRONES QUEEN WORKERS

Differentiaton due to difference in diet

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 some species of animals, sex is determined by environmental conditions or by the presence or absence of the opposite sex

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 d

e

f

2. Determine if the trait recorded in the pedigree below is dominant or recessive. Is it sex-linked or not?

b

d

e

a

c

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

cb

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?

ba

c

f ed

5. The pedigree below shows the blood types of some individuals. List all the possible genotypes of each lettered individuals.

O

A

A

B O

B

O

A B O

e d

AB

a

b

c

f