Genetics and Heredity Overview

Genetics and Evolution - Final Revision Session

• Intended Learning Outcomes: Students will be able to explain genetic material structure and heredity mechanisms, analyze inheritance patterns, discuss evolutionary theory and mechanisms, and understand how inherited and learned traits evolve at the population level.

Assessment Methods

• Written Exam (50%): Genetics exam on 17.12.24. The exam will cover:
  • Structure of genetic material and heredity mechanisms.
  • Analysis of inheritance patterns.
  • The exam will be one hour, divided into two sections:
    • Section A: 60% - short answer and multiple choice questions.
    • Section B: 40% - inheritance patterns using Punnett Squares.
• Assignment 1 (50%): Genetics case study.
• Assignment 2 (50%): Evolution Booklet (1500 words).

What is Genetics?

• Genetics is the study of genes and chromosomes that hold them.
• It's also the science of heredity, explaining similarities between parents and offspring.
• Genes are units of heredity, transferred from parents to offspring, determining traits.
• Humans have approximately 20,000+ genes (genome).

DNA

• DNA (deoxyribose nucleic acid) is the genetic material inherited from parents.
• It's present in all cells' nuclei, tightly packed as chromosomes.
• DNA controls all cellular chemical changes (e.g., cell type formation – muscle, blood, nerve).
• It determines the organism type.

DNA Molecule

• DNA is a large molecule made of nucleotides.
• Nucleotides have three parts:
  • Deoxyribose (a sugar).
  • Phosphate group (-PO4).
  • Organic base (A, C, T, G).

Nucleotides

• Ribose is a sugar similar to glucose, but with five carbon atoms (mRNA).
• Deoxyribose is almost the same but lacks one oxygen atom and found in DNA.

DNA Double Helix

• The paired DNA strands are coiled into a spiral, called the double helix.
• The sugar-phosphate chains are on the outside, while the bases are on the inside.

Replication

• Before cell division, DNA strands unwind and separate.
• Each strand acts as a template to create a new partner strand by adding nucleotides.
• The result is two identical double-stranded DNA molecules in the nucleus.

Chromosomes

• Chromosomes are found in the nucleus.
• Before cell division, chromosomes condense to become visible.
• Proteins called histones attach to DNA, forming chromatin.

Sister Chromatids & Centromere

• Replicated copies of chromosomes are called sister chromatids.
• They join at the centromere.

Chromosomes and Genes

• Since chromosomes are in pairs, corresponding genes are also paired.
• Each member of a gene pair is inherited from either the maternal or paternal parent.

Mitosis

• Mitosis occurs throughout the animal's life, allowing growth and repair of damaged cells.
• It results in two identical cells with the same number of chromosomes (2n).

Meiosis

• Meiosis happens only in sperm and egg cells.
• It results in four haploid (n) cells with half the original number of chromosomes compared to the parent cell.
• Each new cell is genetically unique from each other and the parent cell.

Mendel's Laws of Genetics

• Mendel used mathematics, quantitatively explaining his experiments on inheritance.
• He predicted the concept of genes occurring in pairs, one gene from each pair being passed to gametes.

Dihybrid Cross

• When F₁ generation self-pollinates, four phenotypes (for example, tall/short, purple/white) are observed in a specific ratio.

Linked Genes

• If genes are physically close on the same chromosome, they are often inherited together.
• Independent assortment of linked genes is less likely compared to genes on separate chromosomes.

Incomplete Dominance

• When a heterozygous genotype results in an intermediate phenotype, it is called incomplete dominance.
• Both alleles are expressed to some extent.

Co-dominance

• In co-dominance, both alleles contribute completely to the phenotype, and the appearance is a mix of both.

Sex Chromosomes

• Females have XX chromosomes, males have XY.
• The Y chromosome is smaller than the X; traits on the Y chromosome are passed from fathers to sons.
• X-inactivation in females involves one X chromosome being randomly inactivated during embryonic development.

Sex-Linked Punnett Squares

• Some traits, like coat color in cats, are determined by genes on the sex chromosomes.
• Males and females can exhibit different phenotypes based on X-linked genes.

Polygenic Traits

• Many traits are controlled by two or more genes, resulting in a range of possible genotypes and phenotypes.
• These traits can be greatly influenced by environmental factors.

Epistasis

• Epistasis is when one gene's expression modifies or impacts the phenotypic expression of another gene.

DNA Transcription and Translation

• Steps in the DNA process for creating proteins.
• Transcription converts DNA into mRNA, which travels from the nucleus to the cytoplasm.
• Translation converts mRNA into a protein.

Types of Mutations

• Mutations are changes in DNA.
  • Germline changes are heritable, somatic changes are not.
  • Point mutations alter single nucleotides.
  • Frameshift mutations shift the reading frame in DNA.

Genetic Engineering

• Techniques for modifying genes by inserting them into another organism, such as introducing genes to bacteria to do a task, introducing genes to make a different type of plant, or improving crops.
• Restriction enzymes are used to cut DNA at specific points.

Cloning

• Natural cloning occurs in asexual reproduction.
• Artificially, the nucleus from a body cell is transferred into an egg cell to create a clone of the body cell.

Stem Cells

• Stem cells are undifferentiated cells with the potential to develop into various body cells.
• Embryonic stem cells can create all body cells.
• Some specialized body tissues, such as skin and bone marrow, have stem cell characteristics that can be manipulated to produce specific cells.