The Basics of Inheritance Flashcards
What is an allele?
An allele is a different version of a gene. Each gene has two alleles, one from each parent. These alleles determine traits, such as eye color or hair type. For example, the gene for eye color may have an allele for brown eyes (B) and an allele for blue eyes (b).
What is the difference between a genotype and a phenotype?
A genotype is the genetic code an organism has (e.g., Bb, BB, or bb for eye color). A phenotype is the physical trait that results from that genotype (e.g., brown or blue eyes). Even if someone carries a recessive allele (Bb), their phenotype will show the dominant trait (brown eyes) unless they have two recessive alleles (bb).
What is a dominant trait?
A dominant trait is a characteristic that appears if at least one dominant allele is present. It “overpowers” a recessive allele. For example, in eye color, the B allele for brown eyes is dominant, so someone with BB or Bb will have brown eyes.
What is a recessive trait?
A recessive trait only appears if an organism inherits two copies of the recessive allele. For example, blue eyes (b) are a recessive trait, so a person must have bb (one recessive allele from each parent) to have blue eyes. If they have Bb, the dominant brown (B) will be expressed instead.
What does homozygous mean?
A: Homozygous means having two identical alleles for a gene.
Homozygous dominant: BB (both alleles are dominant).
Homozygous recessive: bb (both alleles are recessive).
This determines whether a dominant or recessive trait is expressed.
What does heterozygous mean?
Heterozygous means having two different alleles for a gene (e.g., Bb). The dominant allele (B) will determine the phenotype, while the recessive allele (b) is hidden but can still be passed on to offspring.
What is co-dominance?
In co-dominance, both alleles are fully expressed, meaning neither is dominant over the other. For example, in AB blood type, a person inherits A from one parent and B from the other, and both are expressed equally, resulting in blood type AB.
What is incomplete dominance?
: In incomplete dominance, the two alleles blend together to create an intermediate phenotype. For example, if a red flower (RR) is crossed with a white flower (R’R’), the offspring will have pink flowers (R R’) because neither allele is completely dominant.
How does a Punnett square help predict inheritance?
A Punnett square is a grid that shows how alleles from parents combine in their offspring. It helps predict the probability of different genotypes and phenotypes. For example, if one parent is Bb (brown eyes) and the other is bb (blue eyes), their children have a 50% chance of Bb (brown eyes) and a 50% chance of bb (blue eyes).
If a mother is homozygous dominant for brown eyes (BB) and the father is heterozygous (Bb), what percentage of their children will have brown eyes?
100% of their children will have brown eyes because every child will inherit at least one B allele:
BB × Bb results in 50% BB and 50% Bb, both of which cause brown eyes.
Since B is dominant, all children will have brown eyes, even if some carry the recessive b allele.
Q: In incomplete dominance, if a red carnation (RR) is crossed with a blue carnation (R’R’), what are the possible genotypes and phenotypes of the offspring?
A:
Genotypes: 100% R R’ (heterozygous)
Phenotypes: 100% Purple flowers
📌 Explanation: Since all offspring inherit one R (Red) allele and one R’ (Blue) allele, they all appear purple because neither allele is fully dominant.
In incomplete dominance, what is the expected outcome when two purple carnations (R R’) are crossed?
A:
Genotypes:
25% RR (Red)
50% R R’ (Purple)
25% R’R’ (Blue)
Phenotypes:
25% Red 🌺
50% Purple 💜
25% Blue 💙
📌 Explanation: Each offspring has a 1 in 4 (25%) chance of inheriting two R alleles (Red), a 1 in 2 (50%) chance of inheriting one R and one R’ (Purple), and a 1 in 4 (25%) chance of inheriting two R’ alleles (Blue).
