BIO202 - Genetics & Heredity Flashcards

Question 1

Law of Segregation (Mendel's First Law)

Accepted Answer

States that an organism carries two alleles for each gene, which separate (segregate) during gamete formation (meiosis) so that each gamete carries only one allele for each gene.

Question 2

Law of Independent Assortment (Mendel's Second Law)

Accepted Answer

States that alleles of two (or more) different genes get sorted into gametes independently of one another, provided the genes are located on different chromosomes or far apart on the same chromosome.

Question 3

Gene vs. Allele

Accepted Answer

A **gene** is a specific sequence of DNA that encodes a functional product (protein or RNA). An **allele** is a specific variant or alternative form of a gene (e.g., eye color gene vs. blue eye allele).

Question 4

Genotype vs. Phenotype

Accepted Answer

**Genotype** refers to the specific genetic makeup or allele combination of an organism (e.g., $Aa$). **Phenotype** refers to the observable physical or functional traits resulting from that genotype (e.g., brown eyes).

Question 5

Incomplete Dominance

Accepted Answer

A form of intermediate inheritance where neither allele is completely dominant, resulting in a heterozygous phenotype that is a blend of both homozygous phenotypes (e.g., red $RR$ $	imes$ white $rr$ $ightarrow$ pink $Rr$).

Question 6

Codominance

Accepted Answer

A genetic scenario where both alleles for a gene are fully and simultaneously expressed in the heterozygous phenotype (e.g., ABO blood group $I^A I^B$ producing type AB blood).

Question 7

Monohybrid Cross Ratios

Accepted Answer

For two heterozygous parents ($Aa 	imes Aa$):
- **Genotypic Ratio:** $1\,AA : 2\,Aa : 1\,aa$ ($1:2:1$)
- **Phenotypic Ratio:** $3	ext{ Dominant} : 1	ext{ Recessive}$ ($3:1$)

Question 8

Dihybrid Cross Phenotypic Ratio

Accepted Answer

The classic phenotypic ratio produced by crossing two individuals heterozygous for two unlinked genes ($AaBb 	imes AaBb$) is **$9:3:3:1$**.

Question 9

Testcross

Accepted Answer

A cross performed between an individual displaying a dominant phenotype (genotype unknown: $A\_$ ) and an individual with a homozygous recessive genotype ($aa$) to determine if the dominant parent is homozygous or heterozygous.

Question 10

Sex-Linked Traits (X-Linked Recessive)

Accepted Answer

Traits caused by genes on the X chromosome. Males ($XY$) are hemizygous and will express the trait if they inherit a single recessive allele, making X-linked recessive disorders significantly more common in males.

Question 11

Gene Linkage

Accepted Answer

The tendency of genes located close together on the same chromosome to be inherited together during meiosis, violating Mendel's Law of Independent Assortment.

Question 12

Recombination Frequency Equation

Accepted Answer

Calculated as:
$$	ext{Recombination Frequency (RF)} = \left( \frac{	ext{Number of Recombinant Offspring}}{	ext{Total Offspring}} ight) 	imes 100\%$$
$1\%$ recombination frequency equals $1	ext{ map unit}$ ($1	ext{ cM}$ or centimorgan).

Question 13

Hardy-Weinberg Allele Frequency Equation

Accepted Answer

For a gene with two alleles ($A$ and $a$):
$$p + q = 1$$
Where $p$ is the frequency of the dominant allele ($A$) and $q$ is the frequency of the recessive allele ($a$).

Question 14

Hardy-Weinberg Genotype Frequency Equation

Accepted Answer

For a population in equilibrium:
$$p^2 + 2pq + q^2 = 1$$
- $p^2$: Frequency of homozygous dominant genotype ($AA$)
- $2pq$: Frequency of heterozygous genotype ($Aa$)
- $q^2$: Frequency of homozygous recessive genotype ($aa$)

Question 15

Conditions for Hardy-Weinberg Equilibrium

Accepted Answer

Five essential assumptions:
1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size (no genetic drift)
5. No gene flow (no migration)

Question 16

Silent Mutation

Accepted Answer

A single nucleotide substitution (point mutation) that changes a codon to another codon coding for the **same amino acid**, resulting in no change to the translated protein.

Question 17

Missense Mutation

Accepted Answer

A single nucleotide substitution that changes a codon so that it codes for a **different amino acid**, potentially altering protein structure and function.

Question 18

Nonsense Mutation

Accepted Answer

A point mutation that converts an amino-acid-coding codon into a premature **stop codon** (UAA, UAG, UGA), truncating the polypeptide chain.

Question 19

Frameshift Mutation

Accepted Answer

An insertion or deletion of a number of nucleotides not divisible by three, shifting the translational reading frame and completely altering all downstream amino acid sequences.

Question 20

Epistasis

Accepted Answer

A form of gene interaction in which the allele of one gene hides, masks, or modifies the phenotypic expression of an allele at a completely different gene locus.

Question 21

Pleiotropy vs. Polygenic Inheritance

Accepted Answer

- **Pleiotropy:** A single gene influences multiple, seemingly unrelated phenotypic traits (e.g., Sickle-cell allele).
- **Polygenic Inheritance:** Multiple independent genes contribute additively to a single phenotypic trait (e.g., human height or skin color).

BIO202 - Genetics & Heredity

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