Inheritance Flashcards
What is monohybrid inheritance?
The inheritance pattern of one gene
What is a gene?
Sort section of DNA found on a chromosome that codes for a particular trait
What is a chromosome?
Long chain on DNA that contains genes
What is an allele?
Different versions of a particular gene
What is a genotype?
Description of the alleles an individual carries for a particular trait
What is a phenotype?
The physical expression of an individual’s genotype for a particular trait
What is a dominant allele?
The allele that only needs to be present at least once in the individual’s genotype in order to be expressed in their phenotype
What is a recessive allele?
The allele that must be present twice in an individual’s genotype in order to be expressed in the phenotype
What is a homozygous genotype?
The genotype for a particular trait contains two identical alleles
What is a heterozygous genotype?
The genotype for a particular trait contains two different alleles
What are the five types of monohybrid inheritance patterns that you have looked at this year?
Complete dominance
Incomplete dominance
Codominance
Multiple alleles
Lethal alleles
Define complete dominance
When one allele is completely dominant over the other. If both are present in the genotype, only the dominant allele will be expressed in the phenotype
Define incomplete dominance
When neither allele is dominant over the other. If both are present in the genotype, neither will be expressed solely in the phenotype and the phenotype is a blend of the two alleles
Define codominance
When both alleles are equally dominant. If both are present in the genotype, both will be expressed in the phenotype
Define multiple alleles
When there are more than two different alleles for a particular trait
Define lethal alleles
When a certain combination of alleles leads to that individual not surviving
Define dihybrid inheritance
The inheritance pattern of two genes
Explain how you determine whether an individual is homozygous dominant or heterozygous for a particular trait
Carry out a test/back cross
Cross the individual with a homozygous recessive individual for that trait and have lots of offpsring
If any offspring display the recessive trait then the unknown parent must have been heterozygous for that trait
If none of the offspring display the recessive trait, then the unknown parent is most likely homozygous dominant
What are unlinked genes?
Two different genes found on the same chromosome
Identify whether linked or unlinked genes create more variation in the offspring and explain why
In unlinked genes, the two different genes can assort independently of each other in meiosis which creates more allele combinations in the gametes, which increases genetic variation. Linked genes stay together in meiosis and don’t assort independently of each other which produces less allele combinations and hence less genetic variation
What would you expect to see if the offspring of linked genes compared to unlinked genes?
Linked genes tend to produce two phenotypes whereas unlinked produce four
The offspring of linked genes tend to reflect the parents phenotypes (3:1 ratio) whereas unlinked genes will have a 9:3:3:1 ratio if both parents are heterozygous for both genes
Explain how you can work out if two genes are linked or unlinked if the individual is heterozygous for both genes?
Cross the individual with a homozygous recessive individual. If the offspring show four phenotypes typically a 1:1:1:1 ratio then they are unlinked. If the offspring show mainly two phenotypes at a ratio of 1:1 then the genes are linked
What are linked genes?
Two different genes found on the same chromosome
Explain how linked genes can produce the other two genotypes and hence phenotypes to increase variation
The linked genes are cross over and be recombined during meiosis which increases the allele combinations and hence variation. This happens randomly and so wouldn’t meet the expected ratios of unlinked genes
