Biology CPE: Monohybrid Cross Quiz - Roberts

gene

A piece of DNA that encodes for a specific protein determining a trait.

locus

The specific location on a chromosome where a gene is found.

homologous chromosomes

Chromosomes that have the same type of gene at the same locus on each chromosome.

allele

A version of a gene.

homozygous

Two alleles for a gene are the same (e.g., AA or aa).

heterozygous

Two alleles for a gene are different (e.g., Aa).

phenotype

The physical expression or observable traits of an organism.

genotype

The genetic makeup of an organism, represented by the alleles it carries.

dominant allele

Expressed in the phenotype if at least one copy is present (uppercase letter, e.g., A).

recessive allele

Expressed in the phenotype only if two copies are present (lowercase letter, e.g., a).

Punnett square

A grid used to predict the possible genotypes and phenotypes of offspring from a genetic cross.

monohybrid cross

A cross that examines the inheritance of only one specific characteristic (e.g., pea shape).

monohybrid cross in a Punnett square

A cross using 1 gene type, 2 alleles, 2 possible gamete genotypes per parent, 4 possible offspring genotypes (may be duplicates), and 25% probability for each grid box.

genotype ratio

The ratio of the different genotypes (e.g., homozygous dominant: heterozygous: homozygous recessive).

phenotypic ratio

The ratio of the different physical traits (e.g., dominant phenotype: recessive phenotype).

genotypic ratio of a heterozygous x heterozygous cross

1 homozygous dominant: 2 heterozygous: 1 homozygous recessive.

phenotypic ratio of a heterozygous x heterozygous cross

3 dominant phenotype: 1 recessive phenotype.

recessive phenotype

It must be homozygous recessive (aa).

dominant phenotype

Its genotype could be homozygous dominant (AA) or heterozygous (Aa).

test cross

A cross between an organism with an unknown genotype (but dominant phenotype) and an organism with the recessive phenotype.

test cross help determine the unknown genotype

If all offspring show the dominant phenotype, the unknown genotype is homozygous dominant (AA). If any offspring show the recessive phenotype, the unknown genotype is heterozygous (Aa).

perform a test cross

Cross the unknown genotype organism with a recessive homozygous organism (aa). If all offspring show the dominant phenotype, the unknown genotype parent is homozygous dominant (AA). If any offspring show the recessive phenotype, the unknown genotype parent is heterozygous (Aa).

Heterozygous x heterozygous cross

The Punnett square will show a genotypic ratio of 1:2:1 (homozygous dominant: heterozygous: homozygous recessive) and a phenotypic ratio of 3:1 (dominant phenotype: recessive phenotype).

Genotypic ratio for AA x Aa cross

1 AA : 1 Aa.

Calculating probabilities from a Punnett square

Each box in the Punnett square represents a 25% chance for a particular genotype to occur, as long as the alleles are equally likely.

Mendel's Law of Segregation

Organisms inherit two copies of each gene (one from each parent) and donate only one copy in their gametes.

Dihybrid cross

A cross that examines the inheritance of two specific traits/characteristics, such as pea color and pea shape.

Law of Independent Assortment

Allele pairs separate independently of each other during gamete formation (meiosis). Different traits are inherited separately.

Monohybrid vs Dihybrid cross

A monohybrid cross looks at one trait, while a dihybrid cross looks at two traits.

Genome

The complete set of an organism's genetic material, determining all of its traits.

Purpose of meiosis

Meiosis produces haploid gametes, each with only one allele from each parent.

Hybrid

An organism with two different alleles for a specific gene (heterozygous).

Purebred

An organism with two identical alleles for a specific gene (homozygous).

Significance of the Punnett square

It allows for predicting the possible outcomes of a cross, including genotype and phenotype probabilities.

Traits not following Mendelian patterns

Most traits occur in a range and do not follow simple patterns (e.g., incomplete dominance, co-dominance, polygenic traits).

Identifying genotype from phenotype

If the organism is showing a recessive phenotype, its genotype must be homozygous recessive (aa). If the organism is showing a dominant phenotype, its genotype could be homozygous dominant (AA) or heterozygous (Aa).

Possible gametes of Aa parent

The possible gametes are A and a.

Difference between genotype and phenotype

Genotype refers to the genetic makeup (e.g., AA, Aa, aa), while phenotype refers to the physical expression of a trait (e.g., purple flowers, white flowers).

Dominant allele representation

A dominant allele is represented by an uppercase letter (e.g., A).

Recessive allele representation

A recessive allele is represented by a lowercase letter (e.g., a).

Difference between gene and allele

A gene is a piece of DNA that codes for a protein, while an allele is a version of that gene.

Inheritance of alleles

Each parent donates one allele to its offspring, which combine to form the genotype of the offspring.

Purpose of a Punnett square in predicting offspring

It helps determine all possible genotypes and phenotypes of offspring resulting from a genetic cross.

Heterozygous x homozygous recessive cross

The offspring will be 50% heterozygous and 50% homozygous recessive, resulting in a phenotypic ratio of 1:1.