10th Biology Chapter 17 Key Points

KEY POINTS

1.  Parents transmit characters to offspring through genes in their gametes. Genes are units of inheritance. These are linearly arranged at specific loci on chromosomes in the form of linkage groups.

2.  Mutations produce different alleles of a gene. Crossing over reshuffles the arrangement of alleles in a linkage group. Genetic recombination produces variations that provide raw material for evolution.

3. Genes are short lengths of DNA in chromosomes. DNA is the hereditary material. It stores genetic information in the sequence of its bases in a linear order. It is a unique molecule best suited to store, copy, and transmit biological information from generation to generation.

4. Genotype expresses into phenotype.

5. DNA of every individual is unique.

6. Mendel laid the foundation of genetics by formulating fundamental laws of heredity. He perceived concept of gene at a time when no one knew about chromosomes or DNA.

7. Many autosomal normal human traits and hereditary diseases like sickle-cell anaemia and diabetes mellitus are transmitted in classical Mendelian fashion.

8. X and Y chromosomes are sex chromosomes because these have sex determining genes.

9. Pattern of sex-linked inheritance is different from autosomal inheritance. A recessive sex-linked trait like color blindness or hemophilia zigzags from maternal grandfather through a carrier daughter to a grandson. Y-linked traits like maleness pass directly form father to son only.