Genetics - Mendelian Inheritance & Population Genetics Flashcards

Question 1

What is a test cross and why is it used?

Accepted Answer

A test cross involves breeding an individual with an unknown genotype (showing the dominant phenotype) with a homozygous recessive individual. It's used to determine if the unknown individual is homozygous dominant or heterozygous.

Question 2

What is a gene?

Accepted Answer

A segment of DNA that codes for a specific protein or functional RNA molecule, determining a particular trait.

Question 3

What is an allele?

Accepted Answer

An alternative form of a gene, found at the same locus on homologous chromosomes.

Question 4

Distinguish between genotype and phenotype.

Accepted Answer

**Genotype** refers to the genetic makeup of an individual (e.g., `AA`, `Aa`, `aa`), while **phenotype** is the observable physical or biochemical characteristics expressed by that genotype (e.g., tall, short, red eyes).

Question 5

Define homozygous and heterozygous.

Accepted Answer

**Homozygous** means having two identical alleles for a particular gene (e.g., `AA` or `aa`). **Heterozygous** means having two different alleles for a particular gene (e.g., `Aa`).

Question 6

State Mendel's Law of Segregation.

Accepted Answer

This law states that during gamete formation, the two alleles for a heritable character separate (segregate) from each other such that each gamete receives only one allele.

Question 7

State Mendel's Law of Independent Assortment.

Accepted Answer

This law states that alleles for different genes assort independently of each other during gamete formation, provided they are on different chromosomes or far apart on the same chromosome.

Question 8

What is the purpose of a Punnett Square?

Accepted Answer

A Punnett Square is a diagram used to predict the genotypes and phenotypes of offspring resulting from a genetic cross, based on the genotypes of the parents.

Question 9

Describe a monohybrid cross and its typical F2 phenotypic ratio.

Accepted Answer

A monohybrid cross involves tracking the inheritance of a single character. When crossing two heterozygotes ($$Aa 	imes Aa$$), the typical F2 phenotypic ratio is $3:1$ (dominant:recessive).

Question 10

Describe a dihybrid cross and its typical F2 phenotypic ratio.

Accepted Answer

A dihybrid cross involves tracking the inheritance of two different characters simultaneously. When crossing two heterozygotes ($$AaBb 	imes AaBb$$), the typical F2 phenotypic ratio is $9:3:3:1$.

Question 11

Explain incomplete dominance.

Accepted Answer

Incomplete dominance occurs when the phenotype of heterozygotes is intermediate between the phenotypes of the two homozygotes (e.g., a red flower and a white flower producing pink offspring).

Question 12

Explain codominance.

Accepted Answer

Codominance occurs when both alleles in a heterozygote are fully and simultaneously expressed, resulting in offspring with a phenotype that shows both parental traits (e.g., ABO blood group `AB` expresses both A and B antigens).

Question 13

What is autosomal dominant inheritance?

Accepted Answer

A mode of inheritance where a single copy of a disease allele on an autosome is sufficient to cause the disease. Affected individuals typically have an affected parent, and the trait appears in every generation.

Question 14

What is autosomal recessive inheritance?

Accepted Answer

A mode of inheritance where two copies of a disease allele on an autosome are required for the disease to manifest. Affected individuals often have unaffected parents (carriers), and the trait can skip generations.

Question 15

What is X-linked inheritance?

Accepted Answer

A mode of inheritance where the gene responsible for the trait is located on the X chromosome. Males are more frequently affected than females because they only have one X chromosome. Affected fathers cannot pass the trait to their sons.

Question 16

Define population genetics.

Accepted Answer

The study of how genetic variation changes within populations over time, focusing on allele and genotype frequencies.

Question 17

What is a gene pool?

Accepted Answer

The total aggregate of genes and their alleles in a population at any one time.

Question 18

State the Hardy-Weinberg equilibrium equation and what each term represents.

Accepted Answer

The equation is $$p^2 + 2pq + q^2 = 1$$, where:
*   $p^2$ = frequency of homozygous dominant genotype (`AA`)
*   $q^2$ = frequency of homozygous recessive genotype (`aa`)
*   $2pq$ = frequency of heterozygous genotype (`Aa`)
Also, $$p + q = 1$$, where $p$ is the frequency of the dominant allele and $q$ is the frequency of the recessive allele.

Question 19

What does the Hardy-Weinberg equilibrium describe?

Accepted Answer

It describes a hypothetical population that is not evolving, meaning allele and genotype frequencies remain constant from generation to generation. It serves as a null hypothesis for evolutionary change.

Question 20

List the five conditions (assumptions) for a population to be in Hardy-Weinberg equilibrium.

Accepted Answer

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 21

What is genetic drift?

Accepted Answer

A change in the allele frequencies of a population due to random chance events, particularly significant in small populations. It can lead to the loss of alleles or fixation of others.

Question 22

Distinguish between the bottleneck effect and the founder effect in genetic drift.

Accepted Answer

**Bottleneck effect**: Occurs when a population undergoes a drastic reduction in size due to a sudden environmental change, leading to a non-representative gene pool in the surviving population.
**Founder effect**: Occurs when a small group of individuals separates from a larger population and establishes a new colony, carrying only a subset of the original population's genetic diversity.

Genetics - Mendelian Inheritance & Population Genetics

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