Sex determination in birds:
- Female birds have two different sex chromosomes designated as Z and W.
- Male birds have two similar sex chromosomes and called ZZ.
- Such type of sex determination is called female heterogammety and male homogamety.
Sex determination in Honey bee:
- Sex determination in honey bee based on the number of sets of chromosomes an individual receives.
- An offspring formed from the fertilization of a sperm and an egg developed into either queen (female) or worker (female).
- An unfertilized egg develops as a male (drone), by means of parthenogenesis.
- The male have half the number of chromosome than that of female.
- The female are diploid having 32 chromosomes and males are haploid i.e. having 16 numbers of chromosomes.
- This is called haplodiploid sex determination system.
- Male produce sperms by mitosis, they don not have father and thus cannot have sons, but have grandsons.
MUTATION:
- Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and phenotype of an organism.
- In addition to recombination, mutation is another phenomenon that leads to variation in DNA.
- Loss (deletion) or gain (insertion/duplication) of a segment of DNA results in alteration in chromosomes.
- Since genes are located on the chromosome, alteration in chromosomes results in abnormalities or aberration.
- Chromosomal aberrations are commonly observed in cancerous cells.
- Mutations also arise due to change in a single base pair of DNA. This is known as point mutation. E.g. sickle cell anemia.
- Deletion and insertions of base pairs of DNA causes frame shift mutations.
GENETIC DISORDERS:
Pedigree Analysis:
- Analysis of traits in several of generations of a family is called the pedigree analysis.
- In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations.
Autosomal Dominant:
- Affected individuals have at least one affected parent
- The phenotype generally appears every generation
- Two unaffected parents only have unaffected offspring
- Traits are controlled by dominant genes
- Both males and females are equally affected
- Traits do not skip generations
- e.g. polydactyly, tongue rolling ability etc
Autosomal recessive:
- Unaffected parents can have affected offspring
- Traits controlled by recessive genes and
- Appear only when homozygous
- Both male and female equally affected
- Traits may skip generations
- 3:1 ratio between normal and affected.
- Appearance of affected children from normal parents (heterozygous)
- All children of affected parents are also affected.
- e.g.- Albinism, sickle cell anaemia etc
CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : harekrushnagiri@yahoo.com
