Chapter 4 -Mendelian Genetics Flashcards
Define Homozygous
Same genes eg AA
Define Heterzygous
Different genes eg Aa
Define Genotype
Genetic makeup of the organism
Define Phenotype
Physical makeup of the organism
Based on the genotype and environment
Answer a punnet square question
- Define alleles
- Do cross
- Use punnet square
- % genotype and % phenotype
Monohybrid cross
A cross showing the probabilities of genotypes and phenotypes from one pair of alleles that determine one trait
Test cross
Parents showing dominant trait could be TT or Tt
- A test cross is the matting/crossing of an organism showing the dominant phenotype, to determine its genotype
- Always across with a homozygous recessive organism. If some or any offspring show the recessive trait, the organism in question must be heterozygous.
- To identify whether an organism exhibiting a dominant allele is homozygous or heterozygous for a specific allele, a scientist can perform a test cross.
- The organism in question is crossed with an organism that is homozygous recessive for that same trait, and the offspring of the test cross are examined - If the offspring produce any recessive traits, it indicates the organism in question is heterozygous.
Incomplete dominance
One trait isn’t dominant over the other so neither is expressed
Eg RR x WW = Pink
R = red. W = white
Codominance
The alleles for a trait are equally expressed
Eg WW x RR = roan
Multiple allele system
Multiple alleles exist in a population when there are many variations of a gene present. In organisms with two copies of every gene (diploid organisms) each organism has the ability to express two alleles at the same time.
- In mono hybrid crosses we have one pair (2) genes that determine a trait.
- In multiallelic systems, there are more than 2 alleles.
- In the case of the ABO blood group system, there are 3 potential alleles I ᴬ, I ᴮ, i.
▪ Iᴬ = immunoglobulin A
▪ Iᴮ = immunoglobulin B
▪ i = no markers
- Iᴬ or Iᴮ is dominant to i.
- Iᴬ is codominant to Iᴮ
Possible genotypes for blood group A
IᴬIᴬ = A Iᴬi = A
Possible genotypes for blood group B
IᴮIᴮ = B Iᴮi = B
Possible genotypes for blood group O
ii = O
Possible genotypes for blood group AB
IᴬIᴮ = AB
Sex linked genetics
Sex linked genetics or X-linked, refers to the inheritance pattern observed when studying genes carries on the X-chromosome.
Males only inherit one X-chromosome. Therefore, they are said to be hemi-zygous for genes on the X-chromosome.
Sex linked genetics rules
- If the female is affected (X ᴴ X ͪ), then all daughters are all at least carriers. All sons are affected.
- If the male is affected (X ͪ Y,) then all the daughters are at least carriers.
- If the mother is a carrier (X ᴴ X ͪ) 50% of the sons will be affected. 50% of the daughters will at least be a carrier.
Dominant sex linked genetics
R= retts syndrome r = normal X ᴿ X ᴿ = retts syndrome X ᴿ X ͬ = retts syndrome X ͬ X ͬ = normal X ͬ Y = normal X ᴿ Y = retts syndrome
Dihybrid cross
A punnet square where you can predict the probabilities of 2 contrasting characteristics at the same time, using 2 pairs of genes
Remember 9:3:3:1
( dominance dominance : dominance recessive : recessive dominance : recessive recessive)
Sex linked condition examples
Red and green colour blindness and haemophilia and DMD (Duchene Muscular Dystrophy).
Define allele
Remember alternate forms of a gene
Eg different coloured eyes
