GED Science Heredity and DNA Summary

DNA (deoxyribonucleic acid) is found in chromosomes. Its sequence of bases holds the instructions (genes) for making proteins, which shape an organism's traits.

Wrong choices

• Glucose: Glucose is a sugar used for energy.
• Starch: Starch is a stored form of sugar in plants.
• Protein: Proteins are made by following DNA's instructions. They do not store the instructions.

A dominant allele shows its trait even when only one copy is present. Pp has one dominant P, so the flowers are purple. The recessive p is hidden.

Wrong choices

• White: White flowers appear only when a plant has two recessive alleles (pp).
• Half purple and half white: The dominant allele controls the whole trait. The flowers are not split.
• Pink: With complete dominance, the traits do not blend into pink.

1. Each parent can pass on P or p.
2. The Punnett square gives PP, Pp, Pp, and pp.
3. Only pp is white: 1 out of 4 = 25%.

Check: 1 PP + 2 Pp + 1 pp = 4 boxes.

Wrong choices

• 75%: 75% is the chance of purple flowers (PP or Pp), not white.
• 0%: Both parents carry p, so a pp offspring is possible.
• 50%: 50% is the chance of a Pp offspring, which is purple.

1. The Pp parent passes P or p. The pp parent always passes p.
2. The Punnett square gives Pp, Pp, pp, pp.
3. Pp is purple: 2 out of 4 = 50%.

Wrong choices

• 75%: 75% is the result for Pp × Pp, not Pp × pp.
• 25%: 25% is the chance of white in a Pp × Pp cross.
• 100%: The pp parent can pass only p, and the Pp parent passes p half the time, so some offspring are white.

A phenotype is an observable trait, such as eye color or height. A genotype is the combination of alleles (such as Bb) that helps produce that trait.

Wrong choices

• Having a gene on chromosome 15: The location of a gene is not a trait you can observe.
• Having a certain order of DNA bases: The DNA base order is genetic information, not an observable trait.
• Having the alleles Bb: Bb is a genotype, the set of alleles a person has.

Each egg and each sperm carries one allele for each gene. When they join, the child has two alleles for that gene: one from each parent.

Wrong choices

• Two alleles from the mother and none from the father: Each parent passes on one allele for each gene, not just the mother.
• The alleles form new in each person after birth: Alleles are inherited from parents. They are not made new after birth.
• Both alleles from whichever parent is taller: Height has nothing to do with which parent passes alleles.

The information in a gene (DNA) is copied into messenger RNA (transcription). The RNA is then read to build a protein (translation). This is called the central dogma of molecular biology.

Wrong choices

• DNA → protein → RNA: RNA is made before the protein, not after it.
• RNA → DNA → protein: The usual order starts with DNA, which is copied into RNA.
• Protein → RNA → DNA: This is the reverse of the usual flow.

A recessive trait shows only with two recessive alleles. The child has the trait, so the child is aa and got one a from each parent. The parents do not show the trait, so each must be Aa (a carrier).

Wrong choices

• The child did not inherit the trait from either parent.: The child received one allele from each parent, so the trait was inherited.
• Only the father carries the allele for the trait.: For a recessive trait not on a sex chromosome, the child needs two recessive alleles, one from each parent.
• The trait is dominant, and both parents have two dominant alleles.: If the trait were dominant, a parent with the allele would show it. Neither parent shows it.

A mutation is a change in the DNA base sequence. Mutations can be harmful, helpful, or have no effect. They are the source of new alleles.

Wrong choices

• dominant trait: A dominant trait is one shown with a single allele. It is not a change in DNA.
• phenotype: A phenotype is an observable trait, not a change in DNA.
• Punnett square: A Punnett square is a chart used to predict offspring.

In Siamese cats, the gene for dark color works best at cooler temperatures. The cat's DNA stays the same, but temperature changes whether the gene's effect shows. This is an example of the environment affecting the expression of a trait.

Wrong choices

• Fur color in these cats is not controlled by genes.: The color pattern is inherited, so genes are involved. Temperature only changes how the gene works.
• The cat's dark fur trait was passed on by the vet.: Traits are not passed on by a vet. The cat already had the gene.
• Cooling the skin changed the cat's DNA.: The DNA did not change. The same gene simply worked differently at a cooler temperature.