Genetics Study Notes - Unit 8...

Unit 8: Genetics

Introduction to Genetics

  • Heredity: The transmission of traits from one generation to the nect parents edited into her the future generation traits

  • Genetics: The scientific study of heredity, which began with Gregor Mendel’s experiments. genius scietfific study helps us become geniuses about thd inherited traits

    • Mendel's work focused on characters and traits: Characters are heritable features that vary among individuals, whereas traits are the specific variants of a character.

    • Mendel \

  • character vs trait character is category(floer color) while trait is type so such as purple or white

Mendel's Experiment

  • Procedure:

    1. A stamen from ay

      that could be classified as dominant or recessive:

    • Flower color:

    • Dominant: Purple

    • Recessive: White

    • Flower position:

    • Dominant: Axial

    • Recessive: Terminal

    • Seed color:

    • Dominant: Yellow

    • Recessive: Green

    • Seed shape:

    • Dominant: Round

    • Recessive: Wrinkled

    • Pod shape:

    • Dominant: Inflated

    • Recessive: Constricted

    • Pod color:

    • Dominant: Green

    • Recessive: Yellow

    • Stem length:

    • Dominant: Tall

    • Recessive: Dwarf

Mendel’s Laws

Mendel’s Law of Segregation

  • Describes the inheritance of a single character:

    • Hypothesis 1: There are alternative versions of genes (alleles) accounting for variations in inherited characters.

    • Hypothesis 2: For each character, an organism inherits two alleles of a gene, one from each parent.

    • Homozygous: An organism with two identical alleles for a gene.

    • Heterozygous: An organism with two different alleles for a gene.

    • Hypothesis 3: If the two alleles of a pair differ, one determines the organism’s appearance (dominant allele), and the other has no noticeable effect (recessive allele).

    • Hypothesis 4: A sperm or egg carries only one allele for each inherited character due to segregation during gamete formation.

Cross Breeding of Homozygous Parents

  • Experiment Steps:

    1. P generation consists of true-breeding parents (purple and white flowers).

    2. F1 generation results: all plants display purple flowers (hybrids).

    3. F2 generation: includes both purple and white flowers after fertilization among F1 plants.

    4. Results yield a phenotypic ratio of 3 purple to 1 white in the F2 generation and a genotypic ratio of 1:2:1 (1 PP: 2 Pp: 1 pp).

The Role of Chromosomes

Homologous Chromosomes

  • In every diploid cell, there are pairs of homologous chromosomes that carry alleles for the same genes at identical locations.

Anatomy of Chromosomes

  • Alleles:

    • Dominant allele: Represented by uppercase letters (P).

    • Recessive allele: Represented by lowercase letters (p).

    • Genotype examples: Homozygous dominant (PP), Homozygous recessive (rr), Heterozygous (Pp).

Mendel’s Law of Independent Assortment

  • Definition: Alleles of one pair segregate independently of another pair during gamete formation.

  • Monohybrid Cross: Cross between individuals heterozygous for one character.

  • Dihybrid Cross: A cross between organisms homozygous for two characters.

Dihybrid Cross Example

  • P generation: RRYY crossed with rryy.

  • Gametes produced: RY × ry.

  • Expected phenotypic ratio in F2 generation from dihybrid cross: 9:3:3:1.

Test Cross

  • Definition: A testcross is a mating between an individual of unknown genotype and a homozygous recessive individual.

  • This can reveal the unknown genotype by examining the offspring produced.

Probability in Genetics

  • Rule of Multiplication: Calculates the probability of two independent events occurring.

  • Rule of Addition: Calculates the probability of an event that can occur in alternative ways.

Family Pedigrees and Genetic Traits in Humans

  • Definition: A pedigree is a family tree that helps determine individual genotypes.

  • Specific traits, such as hairlines (widow's peak versus straight), can be tracked through generations using pedigrees.

Single Gene Disorders

  • Types of Disorders:

    • Recessive Disorders (e.g., Cystic Fibrosis, Albinism) require both parents to be carriers.

    • Dominant Disorders (e.g., Huntington's Disease) can manifest with a single allele.

Variations on Mendel's Laws

Incomplete Dominance

  • Definition: Occurs when the phenotype is intermediate between the parental varieties.

    • Example: Red and white flower parents produce pink hybrids in F1 generation.

Codominance

  • Definition: A situation where both alleles are expressed in heterozygous individuals.

    • Example: ABO blood groups demonstrate three alleles (IA, IB, i) and four phenotypes (A, B, AB, O).

Pleiotropy and Polygenic Inheritance

  • Pleiotropy: A single gene influences multiple traits (e.g., sickle-cell disease).

  • Polygenic Inheritance: Many genes contribute to a single phenotypic character.

    • Example: Human height is a result of multiple genes contributing to the trait.

Sex Chromosomes and Sex-linked Genes

  • Sex Chromosomes in Humans: Males have XY, females have XX.

  • Sex-linked Gene: Genes located on sex chromosomes; X-linked traits exemplify different inheritance patterns, often affecting males more prevalently.