Science 8

What is reproductive probability?

The chance that a specific trait or genetic combination will appear in offspring.

What is a gene?

A segment of DNA that controls a specific trait.

What is an allele?

A version or form of a gene (e.g., B or b).

What does dominant mean?

The allele that is expressed even if only one copy is present (e.g., B).

What does recessive mean?

The allele that is hidden unless two copies are present (e.g., bb).

What is a genotype?

The genetic makeup of an organism (e.g., BB, Bb, bb).

What is a phenotype?

The physical expression of a trait (e.g., brown eyes).

What does homozygous mean?

Having two identical alleles for a trait (BB or bb).

What does heterozygous mean?

Having two different alleles for a trait (Bb).

What is Mendel’s Law of Segregation?

Each parent’s alleles separate during gamete formation so each gamete gets one allele.

What is Mendel’s Law of Independent Assortment?

Alleles for different traits separate independently of one another.

What is the multiplication rule in genetics?

Multiply probabilities when two independent events must both happen.

What is the addition rule in genetics?

Add probabilities when either one of two events can occur.

In a Bb × Bb cross, what are the genotype and phenotype ratios?

Genotypes = 1 BB : 2 Bb : 1 bb; Phenotypes = 3 brown : 1 blue.

What is the probability of blue eyes in a Bb × Bb cross?

25% chance (bb).

What is the phenotypic ratio of a dihybrid cross (RrYy × RrYy)?

9:3:3:1.

What does incomplete dominance mean?

Neither allele is completely dominant; offspring show a blended trait (e.g., red × white = pink).

What does codominance mean?

Both alleles are expressed equally (e.g., blood type AB).

What are sex-linked traits?

Traits carried on the X or Y chromosome (e.g., color blindness, hemophilia).

What are the possible outcomes for two carriers of cystic fibrosis (Ff × Ff)?

25% affected, 50% carriers, 25% unaffected.

What are the possible blood types from AO × BO parents?

25% each: A, B, AB, and O.

If a colorblind father (XʸY) and normal mother (XᴺXᴺ) have children, what are the results?

0% sons affected, all daughters are carriers.

What are the steps to calculate reproductive probability?

1. Identify parent genotypes. 2. List gametes. 3. Fill Punnett square. 4. Count results. 5. Convert to probabilities.

What does a Punnett square show?

The possible genetic outcomes and their probabilities in offspring.

What’s the key idea of reproductive probability?

Inheritance is based on chance, not certainty; Punnett squares predict possible, not guaranteed, results.