Topic 3.2: Simple Inheritance Introduction Flashcards
Distinguish between the terms genotype and phenotype
The phenotype of an individual is its appearance, which is determined by the genes it carries for traits carried in its genome. The genes present in the genome comprise its genotype.
Explain the purpose of testcross.
A testcross is conducted to determine if an individual that is expressing a dominant allele is heterozygous or homozygous for that gene.
Summarize Mendel’s law of segregation
The law of segregation states that each individual has two factors for each trait and these factors separate during gamete formation such that each gamete contains only one factor. At fertilization, the zygote receives two factors for each trait.
Summarize Mendel’s law of independent assortment.
The law of independent assortment states that during gamete formation, each pair of factors separates independently of other factors and that all possible combinations of factors can occur.
Describe the types of crosses that result in a 3:1 and a 9:3:3:1 ratio.
A phenotypic ratio of 3:1 results from a one-trait cross and a ratio of 9:3:3:1 results from a two-trait cross.
Define alleles
Alternative form of a gene; alleles occur at the same locus on homologous chromosomes.
Define locus
Physical location of a trait (or gene) on a chromosome.
What is the law of segregation and what does it state?
Mendelian principle that explains how, in a diploid organism, alleles separate during the formation of the gametes.
It states:
- Each individual has 2 factors for each trait.
-The factors segregate (separate) during the formation of gametes.
- Each gamete contains only one factor from each pair of factors.
- Fertilization gives each new individual two factors for each trait.
Define phenotype.
Visible expression of a genotype—e.g., brown eyes or attached earlobes.
Define genotype
Genes of an organism for a particular trait or traits; often designated by letters—for example, BB or Aa.
Define dominant allele
Allele that exerts its phenotypic effect in the heterozygote; it masks the expression of the recessive allele.
Define recessive allele
Allele that exerts its phenotypic effect only in the homozygote; its expression is masked by a dominant allele.
Define homozygous
Possessing two identical alleles for a particular trait.
Define heterozygous
Possessing unlike alleles for a particular trait.
Define monohybrid cross
Cross between parents that differ in only one trait.
Define Punnett square
Visual representation developed by Reginald Punnett that is used to calculate the expected results of simple genetic crosses.
Define testcross
Cross, between an individual with a dominant phenotype and an individual with a recessive phenotype, to determine whether the dominant individual is homozygous or heterozygous.
What is the law of independent assortment and what does it state?
Mendelian principle that explains how combinations of traits appear in gametes; see also independent assortment.
- Each pair of factors separates independently (without regard to how the others separate.)
- All possible combinations of factors can occur in the gametes.
Define dihybrid cross
Cross between parents that differ in two traits.
The law of segregation states all of the following except
a) factors separate during formation of the gametes
b) each individual has two factors for each trait
c) gametes contain a single factor for each trait
d) factors assort independently of each other by meiosis.
d) factors assort independently of each other by meiosis.
If two parents with short fingers (dominant) have a child with long fingers, what is the chance their next child will have long fingers?
a) There is no chance.
b) 1/16
c) 1/2
d) 3/16
e) 1/4
e) 1/4
Using the products rule, determine the probability that an Aa individual will be produced from an Aa x Aa cross.
a) 25%
b) 50%
c) 75%
d) 100%
e) 0%
b) 50%
According to the law of independent assortment,
a) all possible combinations of factors can occur in the gametes
b) only the parental combinations of gametes can occur in the gametes
c) only the nonparental combinations of gametes can occur in the gametes
a) all possible combinations of factors can occur in the gametes
The genotype of an individual with the dominant phenotype can be determined best by reproduction with
a) a homozygous recessive individual
b) an individual with the dominant phenotype
c) a heterozygote
d) none of the above
a) a homozygous recessive individual
In a dihybrid cross of AaBb x AaBb, what is the probability that offspring will have the dominant phenotype for trait A but the recessive phenotype of trait B?
a) 1/16
b)3/16
c) 7/16
d) 916
e) none of the above
a) 1/16
