Genetics and Inheritance Exam Review

Exam Results

  • Exam 3 Results:

    • Grades distribution: A: 4, B: 5, C: 9, D: 7, F: 5

    • Highest score: 100

    • Average score: 72

Genetics and Inheritance

  • Inheritance refers to the transmission of genetic information from one generation to the next.

  • Genetic information is stored in DNA.

Review of Key Concepts

DNA

  • Central structure of genetics containing genetic information.

Chromosomes

  • Structures made up of DNA and proteins that carry genetic information.

Genes

  • Basic units of heredity made of DNA.

Nucleus

  • The organelle containing DNA in eukaryotic cells.

Vocabulary Terms

  • Gene and Allele:

    • A gene is a sequence of DNA that encodes a trait, while an allele is a variant of a gene.

  • Genotype and Phenotype:

    • Genotype refers to the genetic constitution of an individual, while phenotype is the expression of the genotype, observable in traits.

  • Homozygote and Heterozygote:

    • A homozygote carries two identical alleles for a trait; a heterozygote carries two different alleles.

  • Autosomal vs. Sex-Linked:

    • Autosomal genes are located on chromosomes 1-22, whereas sex-linked genes are located on the sex chromosomes.

Alleles and Mutations

  • Different alleles arise from mutations, defining specific mutations of genes.

  • Example: Hemoglobin gene has normal and sickle-cell variants.

Genotype vs. Phenotype

  • Genotype: Genetic composition (e.g., AA, Aa, aa).

  • Phenotype: Observable characteristics (e.g., red, blue flowers).

Allelic Combinations in Diploid Individuals

  • Diploid individuals have two alleles for each gene.

  • Homozygous: Either both alleles are dominant (AA) or both are recessive (aa).

  • Heterozygous: One dominant and one recessive allele (Aa).

Autosomal vs. Sex-Linked Inheritance

  • Autosomal genes are inherited regardless of the offspring's sex.

  • Sex-linked genes, present on the 23rd pair, determine inheritance patterns based on sex.

Gregor Mendel and Mendelian Genetics

  • Gregor Johann Mendel:

    • Conducted extensive experiments with pea plants between 1856-1863, studying inheritance patterns.

    • Found traits of parents retained in offspring, establishing himself as the “Father of Genetics.”

Mendelian Principles

  • Dominant-Recessive Inheritance:

    • Example: Flower color in peas where B (purple) is dominant over b (white).

  • Cystic fibrosis example:

    • C (normal) and c (abnormal) protein function.

Mendel's Experiments

  • True Bred: Self-pollinated plants producing identical traits.

  • Cross-Pollination:

    • Mixing two true-bred parents produces offspring (F1) reflecting dominant traits.

    • F2 generation may exhibit a 3:1 phenotypic ratio (purple:white).

  • Example of flower color:

    • Cross BB (purple) with bb (white) produces F1 all Bb (purple).

    • F2 from Bb x Bb yields 75% purple and 25% white (suggesting the hidden trait).

The Punnett Square

  • Tools to determine genotypic and phenotypic ratios:

    • Example: BB x bb

    • F1: All Bb.

    • F2: 3 purple (BB, Bb) to 1 white (bb) gives a phenotypic ratio of 3:1.

    • Genotypic ratio of 1:2:1 for homozygous dominant BB, heterozygous Bb, and homozygous recessive bb.

Cystic Fibrosis

  • Pathophysiology: Abnormal CFTR protein leads to thick mucus in the lungs causing infections.

  • Inheritance:

    • Pedigree Analysis: Diseased individuals must be homozygous recessive (cc).

    • Carrier status in parents (CC or Cc) indicating chance of disease in offspring.

Huntington’s Disease

  • Affects individuals between ages 35-60 with a genetic predisposition (autosomal dominant).

  • Symptoms include cognitive decline and behavioral changes.

  • Affected individuals have a 50% chance of passing the allele to their children.

Pedigree Representation

  • Autosomal Dominant: Affected individuals must have an affected parent. Hh vs. hh.

Non-Mendelian Genetics

  • Incomplete Dominance: Results in a third phenotype rather than two distinct traits.

    • Example: Snapdragons with red (RR) and white (WW), resulting in pink (RW) offspring.

Multiple Alleles

  • Genes with more than two alleles.

  • Example: ABO blood groups: A, B, AB, O. Each individual can carry 2 of these alleles.

Polygenic Inheritance

  • Multiple genes interact to affect a single trait (e.g., height).

  • Traits are categorized as continuous (variational) or discrete (distinct).

Environmental Influence on Traits

  • Phenotypic Plasticity: Genotype can produce various phenotypes based on environmental conditions.

    • Equation: Phenotype = Genotype + Environment.