The Chromosome Theory of Heredity • Traits are determined by pairs of genes (alleles) • A pair of genes are located on a pair of chromosomes, one gene for each trait on each chromosome of a pair. • In meiosis, the chromosomes and therefore the genes, segregate independently – one of each pair to a gamete • In fertilization, gametes unite resulting in a fertilized egg that has two genes for each trait carried on pairs of 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 Autosomes (somatic chr) meiosis Gonosomes (sex chr) 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*
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 n n n n sperm n n fertilization parthenogenesis Female larvae (2n) Differentiaton due to difference in diet Male larvae (n) QUEEN WORKERS DRONES
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.
a b c d e f 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 2. Determine if the trait recorded in the pedigree below is dominant or recessive. Is it sex-linked or not?
a b c d 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 f e 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?
O a O A b B O c f A e B d A B AB O 5. The pedigree below shows the blood types of some individuals. List all the possible genotypes of each lettered individuals.