ppt 5 Flashcards
were working with
several traits in sweet peas, notably a gene for purple (P)
vs. red (p) flowers, and a gene for long pollen grains (L)
vs. round pollen grains (l).
William Bateson and R.C. Punnett
is a breeding or a mating between an individual of dominant phenotype, who could be either
homozygous dominant (SS) or heterozygous (Ss), with an
individual that MUST be homozygous recessive (ss)
test cross
the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction.
genetic linkage
Tendency of genes to remain together in their original
combination during inheritance is called
linkage
is defined genetically as the failure of two genes to
assort independently.
linkage
The trend of two or more genes to stay together in the same
chromosome during inheritance is referred to as
linkage
a linkage in which crossing over does not occur. In other words, when only parental types are obtained from the test
cross progeny, it refers to absolute linkage
complete linkage
a linkage in which crossing over occurs between linked genes. As a result along with parental combinations, recombination are also observed in the test cross progeny.
incomplete linkage
It refers to linkage either between dominant genes or
between recessive genes. This type of linkage is found in pea, maize and several other crops.
coupling linkage
It refers to linkage of some dominant genes with some
recessive genes. This type of linkage is found in pea, maize and several other crops.
repulsion linkage
It refers to linkage of such genes which are located
on other sex chromosomes (Autosomes)
autosomal linkage
It refers to linkage of such genes which are located on sex chromosomes
x-chromosomal linkage
types of linkage
- based on crossing over
- based on genes involved
- based on chromosomes involved
The pairing starts at one or more points and proceeds along the
whole length in a zipper manner.
synapsis
Four stranded stage of chromatids occurs
due to splitting of homologous chromosomes into sister chromatids
attached with un-splitted centromeres
duplication of chromosomes
It occurs during pachytene stage. Non-sister chromatids of
homologous pair twist over each other due to action of enzyme
endonuclease.
crossing over
mechanisms of crossing over
- synapsis
- duplication of chromosomes
- crossing over
is formed between two non-sister chromatids of homologous chromosomes
single CROSSING OVER
In this condition, two chiasmata are formed between non-sister chromatids of homologous chromosomes
double-crossing over
Presence of more than two crossovers between non-sister chromatids of homologous chromosomes.
multiple crossing over
types of crossing over
- single crossing over
- double crossing over
- multiple crossing over
importance of crossing over:
- creation of variability
- locating genes
- linkage maps
is the process of determining the genes and
their location along the length of chromosome.
gene mapping
The gene located on same chromosome inherits together
known as
linked gene
