Genetics Chapter 2 Quiz

Transmission Genetics

• Each individual has a unique genome, distinct from those before and after them.
• Transmission genetics describes how genetic differences are passed between generations.

Pea Plant Traits

• Pea plants exhibit various traits including seed color (yellow/green), seed shape (round/wrinkled), pod color (green/yellow), pod shape (smooth/indented), flower color (purple/white), flower position (stem/tip), and plant height (tall/dwarf).

Pea Plant Crossing

• Pea flowers possess sperm and egg-producing structures allowing self-fertilization.
• Mendel's controlled crosses involved removing sperm-producing structures to prevent self-fertilization and ensure specific crosses.
• Mature pollen collected from a flower on the male parent is deposited on the stigma of the female parent to achieve cross-pollination.
• After fertilization, a cloth bag is tied around the fertilized flower to prevent pollen from other plants entering and contaminating the cross.

Yellow vs. Green Seed Traits

• True-breeding strains with yellow seeds and true-breeding strains with green seeds were crossed to produce the first filial (F1) generation, which displayed only yellow seeds
• The trait that appeared in the F1 generation (yellow seeds) is dominant
• The other trait is recessive (in this case, green seeds)

Genotype → Phenotype

• Mendel proposed that a hereditary factor (gene) determines traits.
• Contemporary understanding attributes contrasting traits to different forms of a gene, called alleles.
• Allele combinations constitute an individual's genotype.
• The expressed trait or physical characteristic is the phenotype.

F2 Generation

• The F2 generation (second filial) showed the reappearance of the recessive trait, with a dominant to recessive ratio of 3:1.
• The cross of first generation peas resulted in a second generation (F2) in which there was a reappearance of the recessive trait.

The Principle of Segregation

• Each reproductive cell (gamete) possesses only one allele for each gene.
• Fertilized egg cells (zygotes) are formed via the random combination of gametes from both parents.

The Principle of Independent Assortment

• Segregation of one set of alleles of a gene pair is independent of another set of alleles in a different gene pair, meaning that traits are inherited independently.
• The F2 generation from independent crosses results in a 9:3:3:1 ratio for different seed characteristics.

Segregation of Alleles in Meiosis

• Segregation is the observed separation of homologous chromosomes during meiosis I, ensuring that each gamete receives only one allele for each gene during the process of gamete formation.

Incomplete Dominance

• Neither allele is completely dominant over the other.
• The heterozygous phenotype is intermediate between the two homozygous phenotypes – an example of incomplete dominance.

Codominance

• Both alleles are expressed fully and distinctly in the heterozygous individual.

Probability

• Possible outcomes of a cross are expressed as probabilities ranging between 0 and 1.
• Multiplication rule: probabilities of independent events multiply.
• Addition rule: Probabilities of mutually exclusive events add.

Multiplication Rule

• Probabilities of simultaneous occurrences are products of their individual probabilities if the occurrences are independent.

Addition Rule

• Probabilities of mutually exclusive occurrences are summed.

Addition/Multiplication Rules

• To determine the probability of a particular combination of traits, the multiplication rule can be used for simultaneous, independent events. The addition rule can be used to find the likelihood of any one of several possible mutually exclusive events.

Independent Assortment

• Traits are inherited independently.
• Expected progeny ratio for a dihybrid cross is 9:3:3:1. The possible genotypes can be determined, but there are four phenotypes.

Mendel's Laws

• Mendel's laws of Segregation and Independent Assortment explain inheritance patterns for traits.
• Not all genes display independent assortment, some genes are "linked" together on the same chromosome and do not assort independently.

Epistasis

• Two or more genes interact to affect the same trait.
• The expression/presence of one trait can mask the expression of another.

Patterns of Inheritance in Humans

• Pedigree analysis is used to study inheritance patterns in humans.
• A pedigree chart shows family history of a particular trait to help understand inheritance patterns like whether it's dominant or recessive.

Pedigree of a Dominant Allele

• Affected individuals appear in each generation.
• Affected individuals are equally likely to be male or female.
• Most matings with affected offspring have one affected parent.

Pedigree of a Recessive Allele

• Affected individuals may skip generations.
• Affected individuals are equally likely to be male or female.

Genetic Testing

• Genetic testing identifies genotypes and helps predict trait risk.
• Benefits include personalized healthcare decisions and risk understanding for reduction in anxiety, which impacts quality of life.
• Risks include limited answers, psychological and emotional impact, and concerns regarding privacy and implications on health and life insurance.

Uncommon Inheritance Patterns

• Inheritance can involve genetic material from the mitochondria only passed down through the female parent.

Human Sex Chromosomes

• Very few genes on the Y chromosome have counterparts on the X chromosome, with roughly 1000 genes on the X chromosome and approximately 50 genes on the Y.

Segregation of Sex Chromosomes

• Meiosis in females only produces X-bearing eggs.
• Meiosis in males produces a 1:1 ratio of X-bearing and Y-bearing sperm.
• Random fertilization leads to a 1:1 ratio of male and female offspring.

X-linked Genes

• Traits associated with the X chromosome can be observed in crosses of fruit flies showing recessive mutations; only in males, the ratio of red to white eyes is 1:1 for the F2 generation.

X-linkage

• "Crisscross" inheritance refers to X-chromosome inheritance patterns.
• Males with X-linked recessive traits will have heterozygous carrier daughters and unaffected sons. All F1 offspring will have red eyes.

Heterozygous Cross

• Among progeny from a heterozygous carrier female, half the daughters will be heterozygous carriers, and half of the sons are expected to be affected.

Morgan's Fruit Fly Crosses

• The inheritance pattern of the white-eyed mutation is similar to the pattern of X-chromosome inheritance in fruit flies.

Normal Chromosome Separation

• In normal chromosome separation for X-linked genes in fruit fly crosses, white-eyed females and red-eyed males result in female progeny with red eyes and male progeny with white eyes.

Abnormal Chromosome Separation: Nondisjunction

• Non-disjunction occurs during meiosis resulting in eggs or sperm possessing abnormal numbers of chromosomes.
• Nondisjunction in females produces offspring with XXY females and XO males.

Nondisjunction of Sex Chromosomes in Humans

• Nondisjunction in females can produce eggs with either two X chromosomes or no X chromosome.

Nondisjunction of Autosomes in Humans

• In humans, nondisjunction can occur in autosomes resulting in individuals with extra or missing chromosomes.
• Aneuploidy, such as Trisomy 21 or Down syndrome, can result.

Test your understanding of transmission genetics and Mendelian principles with this quiz. Explore key concepts such as genotype, phenotype, and the ratios from genetic crosses. Answer questions related to Mendel's experiments and principles of inheritance.