8 mistakes learners make with genetics and inheritance, each one named and explained.
Two alleles per gene, one from each parent, and the dominant one shows.
Chromosome, gamete or ribosome is given where allele is wanted.
Half a dozen technical words arrive in one topic and they all sound equally specialised.
Question. The different forms of the same gene
A common answer. chromosomes
The answer. alleles
Why. A chromosome is the whole thread; an allele is one version of one gene on it.
Learn them as a nesting order, biggest to smallest. Then they cannot be substituted.
A heterozygous individual is described as being in between the two features.
Mixing is how almost everything else in the physical world combines.
Question. A Tt pea plant, T tall and t short
A common answer. medium height
The answer. tall
Why. Alleles are separate instructions; they are not mixed together like paint.
Inheritance is particulate. The alleles stay whole and separate through every generation.
Two identical alleles is called heterozygous.
The two words differ by one prefix and are always defined in the same sentence.
Question. Two identical alleles for a gene
A common answer. heterozygous
The answer. homozygous
Why. Homo means same, so homozygous is the one where both alleles match.
The prefix carries the whole meaning, and it is the same prefix as in homogeneous.
A Bb by Bb cross is read as 1 to 1, or a carrier cross is given as a 50 per cent risk.
Three of the four boxes look alike at a glance, and one of them is easy to lose.
Question. Bb crossed with Bb
A common answer. 1:1
The answer. 3:1
Why. The four boxes are BB, Bb, Bb and bb: three show the dominant feature and one does not.
Fill all four boxes, then group them. Never count before the grid is finished.
1 to 2 to 1 is given where the question asked for the ratio of features shown.
Both ratios come out of the same grid, and both are correct answers to some question.
Question. Ratio of dominant to recessive phenotypes from Bb x Bb
A common answer. 1:2:1
The answer. 3:1
Why. Phenotype is what you can see, and BB and Bb look identical.
Genotype counts the letters. Phenotype counts what you would actually observe.
A Tt plant is described as short, because the recessive allele is present.
Both alleles are visibly there in the genotype, so it seems unfair that only one counts.
Question. A pea plant with genotype Tt, where T is tall
A common answer. short
The answer. tall
Why. The dominant allele is expressed whenever it is present, whatever it is paired with.
The recessive feature appears only when there is no dominant allele at all.
Two X chromosomes, or two Y chromosomes, is given as what makes a human biologically male.
X and Y are learned as a pair and which combination is which is a bare fact with no logic behind it.
Question. What makes a human biologically male
A common answer. two X chromosomes
The answer. one X and one Y
Why. Everyone has at least one X. The Y is the one that is present in only one of the two cases.
The Y is the deciding chromosome, and nobody has two of them.
Having 46 chromosomes is given as what determines biological sex.
46 is the number most firmly attached to human chromosomes, so it surfaces first.
Question. What determines biological sex
A common answer. having 46 chromosomes
The answer. having one X and one Y
Why. Every human body cell has 46, so it cannot distinguish anybody from anybody.
A fact that is true of everybody can never be the answer to what makes someone different.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.