Mendelian Genetics Q&A

Who is considered the “father of genetics” and why?

Gregor Mendel; he studied pea plants and discovered patterns of inheritance, establishing the foundation of genetics.

What is inheritance or heredity?

The process by which traits are passed from one generation to the next.

What are true-breeding (P) plants?

Plants that always produce offspring with the same trait.

How did Mendel prevent self-fertilization during cross-pollination?

He removed the male organs of the plant receiving pollen.

What is the parent (P) generation?

The original plants used in a cross.

What happened when Mendel crossed yellow and green seed plants?

All F1 offspring were yellow; green did not appear.

What is the F2 generation and what did it show?

Offspring of F1 plants self-fertilizing; showed a 3:1 yellow to green ratio.

Which trait is dominant and which is recessive in Mendel’s pea seed color?

Yellow = dominant; Green = recessive.

What is an allele?

An alternative form of a gene that passes from generation to generation.

How did Mendel explain why green seeds reappeared in F2?

The green allele was hidden in F1 (recessive) but segregated out in F2.

How are dominant and recessive alleles represented?

Dominant = capital letter (Y), Recessive = lowercase letter (y).

Define homozygous.

Two identical alleles for a trait (YY or yy).

Define heterozygous.

Two different alleles for a trait (Yy).

Can you tell if a yellow plant is homozygous or heterozygous just by looking?

No, both YY and Yy appear yellow.

Define phenotype.

Observable trait of an organism (what it looks like).

Define genotype.

The combination of alleles inside an organism.

What is a hybrid?

Offspring heterozygous for a trait (Yy).

State Mendel’s Law of Segregation.

Each parent contributes one allele per trait; alleles separate during gamete formation.

What is a Punnett square used for?

To predict possible offspring genotypes from known parent genotypes.

In a monohybrid cross Yy × Yy, what are the possible genotypes?

YY, Yy, yy

Genotypic ratio for Yy × Yy?

1 YY : 2 Yy : 1 yy

Phenotypic ratio for Yy × Yy?

3 yellow : 1 green

Why do genotype and phenotype ratios differ?

Because YY and Yy produce the same phenotype (yellow).

In a 2×2 Punnett square, why are there 4 squares?

Each parent produces 2 types of gametes, so 2 × 2 = 4 combinations.

Genotypes in a 2×2 Punnett square for F × f?

1 FF, 2 Ff, 1 ff

Phenotypic ratio in that 2×2 Punnett square?

3 freckles : 1 no freckles

Traits for a dihybrid cross example?

Seed shape: R = round (dominant), r = wrinkled (recessive); Seed color: Y = yellow (dominant), y = green (recessive)

Parental genotypes in the dihybrid example?

YYRR × yyrr

F1 generation in that dihybrid cross?

All YyRr → yellow round seeds, hybrids

How many gametes does each F1 parent produce in a dihybrid cross?

4 gametes: YR, Yr, yR, yr

How big is the Punnett square for a dihybrid cross?

4 × 4 = 16 squares

Typical phenotypic ratio for F2 in dihybrid cross (YyRr × YyRr)?

9:3:3:1

• 9 = both dominant

• 3 = first dominant, second recessive

• 3 = first recessive, second dominant

• 1 = both recessive

How is inheritance like flipping a coin?

Each allele has a 50% chance of being passed on, like heads/tails in a coin flip

Why don’t small numbers of offspring always match predicted ratios?

Probability can vary in small samples; chance causes deviations.

Why do larger numbers of offspring match predicted Punnett square ratios more closely?

Law of probability evens out with larger sample sizes.