DNA
is a very special molecule which carries information of the species, and individual traits
chromatin
partially coiled DNA (with histones). This is the normal state of the DNA when cell is not dividing (mitosis or meiosis)
Allele
if genes are not the same they are called alleles (blue or green gene for eye colour)
diploid
46
haploid
23
synapsis
Homologous chromosomes pair up
This is called synapsis
tetrad
a group of four chromatids that have similar genes
zygote
fertilized egg cell
chromosome
Chromosomes are large bodies which are composed of one long strand of DNA wrapped around proteins called histones and are supercoiled
gene
Genes are lengths of DNA that carry a code for the structure of proteins. These proteins give us our characteristics
homologous chromosomes
same chromosomes
chromatid
a section of DNA
spindle
controls movement, separation of chromosomes
gamete
a haploid sex cell
what does meiosis show?
variation is heritable
how are mitosis and meiosis different from one another
- mitosis: needs one parent, only 1 phase of cell division to create 2 cells. synapsis does not occur, takes less time, creates two diploid cells. for growth and repair
- meiosis: needs two parents to create fertilized egg. goes through 2 phases of division, synapsis occurs, create 4 haploid daughter cells. for genetic diversity in sexual reproduction
how does meiosis explain Mendel’s principles
Mendel’s principle of segregation: Mendel uses this to infer the behaviour of alleles during sexual reproduction.
Mendel’s principle of dominance: infers interaction of alleles when they combine in a new hybrid individual
Mendel’s principle of independent assortment: each pair of alleles separate independently without regard to how others separate. all possible combinations of factors can occur in equal proportions. this occurs when genes are found on separate chromosomes or very far apart
• Understand the role of probability in genetic crosses
probability does not have memory. each offspring has equal chance for a trait. this is why sometimes, even though it is unlikely, you can have many children of a trait in a row
monohybrid cross
- bred two pure breed parents, with either one trait or two
- F1 generation is 100 dominant trait
- f2 generation shows 3:1 ratio!
principle of segregation
- genes exist in pairs which segregate randomly when gametes are formed and then recombine into pairs at fertilization. sperm and egg and haploid while adult is diploid
principle of dominance:
- if an individual is heterozygous, one factor will dominate over the other, recessive trait will only show up when an individual has two copies of that allele. it must be homozygous
heterozygous individuals can also be called
hybrids
pure breeding:
when population always produces same trait
hybrid
when a population is created from two different pure breeds
