Untitled Quiz

Gregor Mendel and Mendelian Genetics

• Gregor Mendel (1823-1884) studied heredity.
• Mendelian genetics is the study of heredity.
• Mendel worked with pea plants.
• Pea plants are inexpensive, easy to control reproduction, and produce many offspring with contrasting characteristics.
• Contrasting characteristics include: seeds (round or wrinkled), seed color (yellow or green), height (tall or short), flowers (white or purple), and pod color (yellow or green).

Mendelian Genetics: F2 Generation Results

• Mendel's experiments involved cross-pollination of pure plants with contrasting characteristics.
• Examples include:
  • Purple flowers x White flowers
  • Yellow seeds x Green seeds
  • Round seeds x Wrinkled seeds
• The F2 generation (the second filial generation) exhibited traits in a specific ratio, like 3.15:1 for purple to white flowers, and 3.01:1 for yellow to green seeds.

Mendel's Principles of Heredity

• Dominance: One form of a hereditary trait dominates the other.
• Segregation: Segregation of chromosomes during meiosis.
• Recombination: Combining of chromosomes from sperm and egg (fertilization).
• Independent Assortment: Independent segregation of genes forming gametes.

Pea Plant Characteristics

• Peas reproduce sexually.
• Each trait is influenced by two alleles (one from each parent).
• Alleles are represented by letters.

Mendel's Work: The Next Generation

• Mendel cross-pollinated pure plants. For example, he crossed "pure tall" with "pure short".
• The F1 generation (first filial generation) showed only one trait. The offspring were all tall.
• Mendel then used two F1 tall plants and crossed them, creating the F2 generation.
• The F2 generation showed both tall and short traits in a 3:1 ratio.

Punnett Square

• A tool used to predict the outcome of genetic crosses.
• Each box represents a possible offspring.
• Mendel used Punnet Squares accurately predict the outcomes of crosses he didn't even perform.

Hybrid Cross

• A cross between two heterozygotes.
• There are three possible genotypes in a 1:2:1 ratio.
• The phenotypic ratio is 3:1 (3 dominant:1 recessive).

Test Cross

• Determining the genotype of an organism displaying a dominant phenotype by crossing it with a recessive individual.
• If any recessive offspring result, the original individual is heterozygous (hybrid).
• Example: a brown-eyed individual testing for BB vs Bb

Codominance

• Some traits are controlled by two different dominant alleles. Both alleles are expressed.
• Heterozygotes exhibit both phenotypes simultaneously.
• Example: coat color in cattle (Roan).

Incomplete Dominance

• An allele is only partially dominant over another.
• In heterozygotes, the phenotype is a blend of the two homozygous forms.
• Example: Snapdragons (flower color).

Mendel's Law of Independent Assortment

• Two traits are inherited independently if the genes are on different chromosomes.
• During gamete formation, alleles for different traits segregate independently of each other.

Gene Linkage

• If genes for different traits are on the same chromosome, they are linked (inherited together).
• Examples include eye and hair color.
• Crossing over in meiosis can cause recombination of linked genes, increasing variability in the offspring.

Multiple Alleles

• Some traits are controlled by more than two different alleles.
• Example: human blood types (controlled by three alleles: IA, IB, and i).

Sex Determination

• Males and females differ in one pair of chromosomes (sex chromosomes). Humans have 23 pairs of chromosomes in total. XX determines a female and XY determines a male. The man determines the sex of the child.
• In humans, the sex chromosomes are "X" and "Y".
• Genes on the X chromosome are called sex-linked. Often recessive genes on the X chromosome are expressed more often in males because males have only one X chromosome.

Sex Linkage

• Some genes are located on the X chromosome.
• Recessive sex-linked genes are more commonly expressed in males because they only have one copy of the X chromosome.
• Examples include hemophilia and colorblindness. These traits are more frequently observed in males because females need to inherit two recessive alleles.

Pedigree Charts

• Illustrate the inheritance of traits in families.
• A tool used to track the inheritance of genetic traits across multiple generations.
• Example: pedigree illustrating albinism.

Heredity and the Environment

• Environment interacts with genes affecting the expression of inherited traits. Example: effect of light on chlorophyll production in plants. Example: Effect of temperature on the coat color of Himalayan rabbits.