Genetics

" Are you bent or straight? "


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Parental (P) generation - The original cross.

          F1 generation - Offspring of the P generation.

          F2 generation - Offspring of the F1 generation.

Allele - A gene choice - 2 choices for 1 gene.

Homozygous - Has the same allele (choice) on both homologous chromosomes.

          True breeding - Has the same allele (choice) on both homologous chromosomes.

Heterozygous - Has the different alleles (choices) on the homologous chromosomes.

Principle of dominance - One allele can mask the expression of another in a hybrid.

Dominant - Always expressed in a heterozygote.

Recessive - Always hidden in a heterozygote.

Genotype - The alleles the individual carries for a given trait - the letters.

Phenotype - The expression of that trait - what you look like.

Punnett square - Predicts the ratio of the genotype and phenotype of potential offspring.

          Gametes - Sperm or eggs

Monohybrid cross - Both parents are heterozygous for 1 trait.

Test cross - Do you have a heterozygote or a homozygous dominant? Cross the unknown with a homozygous recessive.

Dihybrid cross - Both parents are heterozygous for 2 traits.

Multiple alleles - (of same gene) - are traits which have more than 2 alleles in the population.

          Codominant - Both traits are expressed.

Erythroblastosis fetalis - Rh- woman has a Rh+ baby, her antibodies can kill her second Rh+ baby.

Polygenic inheritance - Is where multiple genes all contribute to the phenotype in additive fashion.

Phenylketonuria   PKU - A homozygous recessive disorder - These people lack the enzyme to convert phenylalanine (amino acid) into the amino acid tyrosine.

          Phenylalanine (Amino acid) ------> Tyrosine (Amino acid) (They instead make a neural toxin)

Sickle cell anemia - A homozygous recessive disorder - Red blood cells are sickle shaped and don't flow through vessels easily.

          Heterozygote advantage - The heterozygote does better than both the homozygotes. - SS     Ss     ss

Cystic fibrosis - A homozygous recessive disorder - The secretions of the body are thick and abnormal.

Huntington's disease - A dominant allele disorder - It leads to muscle spasms, personality changes, and insanity.




		 	  Genotype             	            Phenotype

Homozygous Dominant	Bent / Bent  (BB)		- Bent little fingers 
 ( True Breeder )  

Heterozygous		Bent / Straight  (Bb)	 	- Bent little fingers
         
Homozygous Recessive	Straight / Straight  (bb) 	- Straight little fingers
 ( True Breeder )



     Possible Genotype		 Phenotype

	AA, AO			Type A blood
	BB, BO			Type B blood
	AB (Codominant)		Type AB blood
	OO			Type O blood



   LIGHT	         MEDIUM	   	           DARK

  aabbccdd  --------->  AaBbCcDd  ------------>  AABBCCDD



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Last updated on 2 January 2018