20 flashcards · Shared on 19 August 2026 by AtomAI Library
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What is an allele?
An alternative form of a gene
What is an allele?
An alternative form of a gene
Which term describes an organism's combination of alleles for a gene?
Genotype
What is a phenotype?
The physical or observable expression of a trait
For a gene with alleles A and a, which genotype is heterozygous?
Aa
Which pair contains two homozygous genotypes?
AA and aa
In simple Mendelian inheritance, what makes an allele dominant?
It is expressed in a heterozygous individual
If A is dominant to a, which genotype produces the recessive phenotype?
aa only
What does the law of segregation state?
The two alleles for a gene separate during gamete formation
Which alleles can appear in the gametes of an individual with genotype Aa?
A or a
What does each box inside a Punnett square represent?
A possible allele combination in an offspring
Where are the parental alleles normally placed when constructing a Punnett square?
Along the top and side of the grid
What genotype ratio is expected from the cross Aa × Aa under simple Mendelian inheritance?
1 AA : 2 Aa : 1 aa
If A is completely dominant to a, what phenotype ratio is expected from Aa × Aa?
3 dominant : 1 recessive
What is the probability that a cross between AA and aa produces an Aa offspring?
100%
A heterozygous individual is crossed with a homozygous recessive individual. What proportion of offspring is expected to show the recessive phenotype?
50%
Why is a test cross performed?
To determine whether an individual with a dominant phenotype is homozygous or heterozygous
What is incomplete dominance?
The heterozygote has a phenotype intermediate between the two homozygotes
How does codominance affect the phenotype of a heterozygote?
Both alleles are fully expressed
For two independently assorting genes, what phenotypic ratio is expected from AaBb × AaBb when each gene shows complete dominance?
9:3:3:1
Why might the observed results of a small genetic cross differ from a Punnett square's predicted ratio?
Punnett squares describe probabilities rather than guaranteed outcomes