Need to know about linked genes to variation!?

I kinda finished study about mitosis and meiosis.


Now i have few questions bugging me.





1.what's a test-cross? what information does it give?


2.the genotypic and phenotypic ratios from a mono-hybrid cross


3.Know the phenotypic ratios from a dihybrid cross


4.Understand the relationship of linked genes to variation in crossing over.


5.Understand the effects of non-disjunction.


6.how to get information from a pedigree?


7.Understand how sex-linked traits work.


8.what are linked genes?


Biology is killing me right now ahk! gotta get back to study now. Please help me! you can give me some websites about genetics too!





who's considered the father of genetics? is it Mendel?


I am keep studying with my txtbook. If i get some answers, i will post some. Thank you

Need to know about linked genes to variation!?
1. A test cross is a cross between an organism displaying dominant phenotype to a homozygous recessive organism. It tells you if the genotype of that dominant phenotype organism is homozygous or heterozygous.


2. Genotypic ratio is 1:2:1, phenotypic ratio is 3:1. For example, the monohybrid cross between Tt and Tt give a genotypic ratio or 1TT: 2Tt: and 1tt. Since TT and Tt display dominant phenotype, the phenotypic ratio is 3:1.


3. Dihybrid cross (ex: TtRr x TtRr) gives 9:3:3:1 phenotypic ratio.


4. Linked genes mean they are very close together on the chromosome. This means the probablility of a cross-over event between them is small and alleles of the two loci will be inherited together.


5. Non-disjunction is improper chromosome separation during meiosis (either homologous chromosomes at meiosis 1 or sister chromatids at meiosis 2). The results is gametes with too many or too few chromosomes. This can lead to disorders such as Down's, Klienfelters, Turner's, or poly-x syndrome, or even death if no X chromosome is inherited.


7. Sex linked traits mean the locus is on the X chromosome and inherited with the X. Recessive, x-linked traits like color blindness, are more commonly seen in males because they only get one X chromosome from their mother. If that x is screwed up, then they are screwed up. Females, on the other hand, have two x chromosomes. If they get a screwed up one, then there is a chance the other one will be good.


8. See #4





The father of genetics is typically considered to be Mendel. Especially since you are studying this stuff.

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