Monohybrid Cross + Test Cross Flashcards
What is monohybrid inheritance?
The inheritance of a pair of contrasting characteristics controlled by 2 alleles at a single locus.
Why did Mendel use peas in his experiment?
They are easy to grow
Their flowers can self fertilise and cross fertilise
They make flowers and fruit in the same year
They make a statistically significant large amount of seeds in each cross.
How did Mendel study monohybrid inheritance?
He chose pairs of contrasting characteristics, like yellow/green seeds, tall/dwarf plants, round/wrinkled seeds.
Why were the characteristics Mendel chose good?
Controlled by single genes
Controlled by genes on different chromosomes
Clear cut and easy to tell apart
What are the steps to drawing a monohybrid cross?
- Genotype
- Gametes from each parent - gametes are haploid so only have one allele.
- Construct a grid and put gametes in there
- Carry out genetic cross
- Count the different genotypes and phenotypes and represent them as a percentage or ratio.
Why are test crosses done?
To work out if an individual with a dominant characteristic is homozygous dominant or heterozygous.
What is a test cross?
Involves breeding an individual with an unknown genotype with an individual that is homozygous recessive and looking at the phenotypes of offspring to determine the genotype of the unknown.
What would the results of the genetic cross be if the individual was homozygous dominant and heterozygous?
Homozygous dominant: 100% heterozygous - dominant
Heterozygous: 50/50 heterozygous homozygous.
Define co-dominance.
When both alleles in a heterozygote are expressed. For example in the human ABO blood group, people can be AB
Define incomplete dominance.
When the phenotype of the heterozygote is an intermediate between the two parental phenotypes rather than one being expressed. For example, pink carnations from white and red carnations.
What is Mendels first law (law of segregation).
Every organism possesses a pair of alleles for any particular characteristic. Each parent passes a copy of only one of these alleles and only the dominant allele affects the phenotype.
What is Mendels second law (the law of independent assortment).
There is nothing to determine which way chromosomes will line up on the equator in meiosis, therefore the chromosomes that the cells have are random. The maternal and paternal alleles randomly mix in different combinations. The genes are unlinked.
