Download Variation

Genetics(I)
 the study of the inheritance of traits by
means of the examination of their
differences.
DNA
 genetic material that is packed in a length
and forms chromosome.
Genetics(II)
Gene
 A short length of DNA on chromosomes
determining inherited characters.
 it can be more than one gene on a
chromosome.
DNA controls different types of proteins
produced and results different body
characters.
Genetics(III)
Cell Division
 Mitosis
 Meiosis
Mitosis(I)
 occurs in somatic(body) cells
 mainly for growth and replacement(e.g.
skin, blood cells)
 no homologous chromosomes pairing and
crossing over
 only one nucleus division occurs
Mitosis(II)
 2 daughter cells are resulted from 1 parent
cell
 no. of chromosomes in daughter cell is
diploid(2n), same as parent cell
Mitosis(III)
Meiosis(I)
 occurs in cells of reproductive organs(e.g.
testis, ovaries) and gametes are resulted
 for gamete formation
 crossing over and homologous chromosome
pairing occur. Crossing over allows genetic
variation occurring in meiosis.
Meiosis(II)
 2 nucleus divisions occur
 4 daughter cells produced
 no. of chromosome in daughter cell is
haploid(n), half of parent cell
Gametes are the products of meiosis. Hence,
they are haploid(n). However, when an egg
cell is fertilized by a sperm. A diploid(2n)
zygote will be formed.
Monohybrid inheritance
Definition
 the inheritance of a single pair of contrasting
character
– cross-pollination of a pair of pure breeding
contrasting character ( PP X pp).
• All F1 generation are hybrid, heterozygous
and have the same genotype (Pp) and
phenotype.
Monohybrid inheritance
– self-pollination of F1
• F2 generation
– genotype ratio = PP :Pp :pp
= 1 :2 :1
– phenotype ratio = 3 : 1
Terms
 alleles - the different forms of a gene and occupy
the same locus on chromosomes.
 dominant - phenotype of an allele expresses itself
at the expense of an alternate allele.
 genotype - the genetic information present for a
particular trait.
Terms
 heterozygous - an alleles on the homologous
chromosomes are different (Pp).
 homozygous - an alleles on the homologous
chromosmes are the same (PP/pp).
 hybrid - an offsprings contains different genes
from the cross between unrelated strains.
Terms
 phenotype - the observable characteristics of an
organism.
 recessive - an allele whose expression is
suppressed in the presence of a
dominant allele.
Sex determination
 Human’s sex is determined by whether an
individual contains an “Y” chromosome or
not.
– female have 2 X-chromosomes.
– male have 1 X-chromosome and 1 Ychromosome.
Variation
 There are 2 types of variations:
 1.)Continuous variation
---there is no clear-cut and have many
intermediate values that forms a bellshaped distribution. Genetics and
environment can affect it.
E.g.: bodies weight and IQ
 2.) Discontinuous variation:
---there is a clear cut and no any
intermediate values. It is inborn.
E.g.: ear-lobes and roll of the tongue
Causes of variation
 1.) Meiosis
---there are random fertilization and then get
random combination of the genes in zygotes.
 2.) Mutation
--- there is sudden change in the genes.
 3.) Environment
---this is important factor. Characters will be
changed in different situations such as:
a.) Light --it affects the growth of the seedlings.
b.) Temperature---rabbits have different fur
colors in the warm and cold places.
Significance of variation
– This is the IMPORTANT process in evolution.
It is natural selection to find the fittest of
survival. Species will compete for the food and
other resources with others in order to alive.