Biology:2010:CBSE:[All India]:Set-II

In amphibians, syngamy occurs in the external medium (water), ie., outside the body of the organism and hence, is known as external fertilisation.
In reptiles, syngamy occurs inside the body of the organism and hence, called as internal fertilisation.

An autosomal dominant disorder is Myotonic dystrophy.An autosomal recessive disorder is Sickle cell anaemia.

Exonucleases remove nucleotides from the ends of the DNA whereas endonucleases make cuts at specific positions within the DNA.

It represents Genetic Diversity.

The enzyme involved in the continuous replication of the DNA strand is DNA dependent DNA polymerase.
The polarity of the template strand is 3’ 5’.

Offsprings derived from asexual reproduction are called clones because:
1.  They are genetically and morphologically similar to their parents.
2. A single individual is capable of producing the offspring; hence, no genetic recombination occurs.

i. Carrier of sickle cell anaemia: Hb^A Hb^s
ii. Affected individual: Hb^s Hb^s

Characteristic feature-Zoospores are microscopic motile structures.
Function- They are involved in asexual reproduction.

In orange, the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. Each ovule contains many embryos. This phenomenon of occurrence of more than one embryo in a seed is known as polyembryony.

Certain specific restriction endonucleases recognise a specific palindromic nucleotide sequence in the vector as well as foreign DNA and produce staggered cuts which results in the formation of sticky ends. These sticky ends are then joined with the help of specific DNA ligases.