Inheritance & Genetics

Levels of Organization

  • Cell: The basic unit of life.

  • Tissue: A group of similar cells performing a specific function.

  • Organ: A structure composed of different tissues working together.

  • Organ System: A group of organs working together.

  • Organism: A complete living being.

What are Cells Made Of?

  • The four macromolecules:

    • Carbohydrates.

    • Lipids.

    • Proteins.

    • Nucleic Acids.

  • Water.

Proportion of Macromolecules in Cells

  • Water: 70-90\%.

  • Carbohydrates: 3\%.

  • Lipids: 2\%.

  • Proteins: 10-15\%.

  • Nucleic Acids: 5-7\%.

Heredity and Genetics

  • Genetics: The field of biology that studies how traits are passed from parents to offspring.

  • Heredity: The passing of traits from parents to offspring; therefore, genetics is the study of heredity

Traits

  • Traits: Observable characteristics passed down from parent to offspring.

  • Individuals share 99.8\% of their genetic information with everyone else.

  • The remaining 0.2\% makes individuals unique.

Genetic Inheritance

  • Occurs in both sexual and asexual reproduction.

Reproduction

  • Sexual Reproduction: Two organisms contribute DNA to produce a new organism.

  • Asexual Reproduction: One organism provides all the DNA and produces a clone of itself.

  • In both, genetic material is passed from one generation to the next.

Sexual vs. Asexual Reproduction

  • Sexual Reproduction:

    • Involves two parents.

    • Produces genetically different offspring (zygote).

  • Asexual Reproduction:

    • Involves one parent.

    • Produces genetically identical offspring (clones).

Chromosomes and DNA

  • Egg (Ovum): 23 Chromosomes.

  • Sperm: 23 Chromosomes.

  • Fertilization: Zygote with 46 Chromosomes in 23 pairs.

  • Embryo: 46 Chromosomes in 23 pairs.

  • Humans get 50% of their DNA from each parent.

Chromosome Structure

  • DNA: Double helix.

  • Histone: Proteins around which DNA is coiled.

  • Nucleosome: A section of DNA wrapped around a core of histone proteins.

  • Chromatin: The complex of DNA and proteins (histones) that make up chromosomes.

  • Chromosome: A thread-like structure of nucleic acids and protein carrying genetic information in the form of genes.

  • Human Karyotype: We have 46 chromosomes, 23 pairs of chromosomes.

Karyotype

  • A display of the chromosome pairs of a cell arranged by size and shape.

  • Male: XY sex chromosomes.

  • Female: XX sex chromosomes.

Chromosomal Errors

  • Down’s Syndrome (Trisomy 21):

    • Result of inheriting an extra chromosome during fertilization.

    • It is a small chromosome, so not much essential genetic information is affected.

  • Turner’s Syndrome: Only 1 X chromosome.

  • Potential causes of chromosome damage:

    • Radiation.

    • Food Mutagens.

    • Industrial Chemicals.

    • Air Pollution.

Cell Nucleus

  • Every cell in the body has a nucleus, except for red blood cells.

  • Red blood cells lack a nucleus to accommodate maximum space for hemoglobin.

  • The nucleus contains all the cell's DNA.

  • When uncoiled (uncondensed), DNA has a length of 2 meters.

  • When condensed into chromosomes, its size is 6um long, or 0.006mm, or 0.000006cm.

Purpose of DNA Condensation into Chromosomes

  • To make cell division easier.

  • Each chromosome doubles right before division.

Mitosis Stages

  • Interphase.

  • Prophase.

  • Metaphase.

  • Anaphase.

  • Telophase.

Types of Cells and Chromosomes

  • Two types of cells:

    • Sex cells (gametes).

    • Somatic cells (body cells).

  • Two types of chromosomes:

    • Autosomes: Control inheritance of traits.

    • Sex chromosomes: Control sex (male/female) and related traits.

Specific Chromosomes and Their Functions

  • Chromosome 1: Brain and muscle development.

  • Chromosome 4: Skeleton development.

  • Chromosome 11: Sense of smell.

  • Chromosome 19: Eye color and blood type.

  • Chromosome X/Y: Sexual development and puberty.

Meiosis

  • Process by which the number of chromosomes is halved (occurs in sex cells).

Purpose and Process

  • How does this halving happen?

    • In a process called meiosis, where the DNA halves.

  • Meiosis:

    • Only happens in sex cells (gametes).

    • Reduces chromosome number by half (n).

    • Produces haploid cells.

    • When gametes combine to form the zygote, the original chromosome number is restored.

Stages of Meiosis

  • Meiosis is divided into two phases:

    • Meiosis 1: Separates homologous chromosomes (mom sets separate from dad sets).

    • Meiosis 2: Separates sister chromatids (mom sets get split up and dad sets get split up).

Interphase

  • G1: Cells grow and perform many of their required cellular functions.

  • S: DNA is copied (replicated).

  • G2: Makes proteins, grows.

Prophase I

  • Nuclear membrane breaks down.

  • Centrosomes move to opposite sides of the cell.

  • Spindle fibers start to assemble.

  • Duplicated chromosomes condense.

  • Homologous chromosomes pair up.

Metaphase I

  • Homologous chromosome pairs are randomly lined up in the middle of the cell.

  • Chromosomes (some from the father, some from the mother) are lined up along each side of the cell equator.

Anaphase I

  • Paired homologous chromosomes separate from each other and move toward opposite sides of the cell.

  • Sister chromatids remain together.

Telophase I

  • Nuclear membrane forms again (in some species).

  • Spindle fibers disassemble.

  • Cell undergoes cytokinesis.

  • End result: 2 cells that each have a unique combination of 23 duplicated chromosomes coming from both parents.

Prophase II

  • Nuclear membrane breaks down.

  • Centrosomes move to opposite sides of the cell.

  • Spindle fibers assemble.

Metaphase II

  • Spindle fibers align chromosomes at the cell equator.

  • Each chromosome still has two sister chromatids.

Anaphase II

  • Sister chromatids are pulled apart from each other.

  • They move to opposite sides of the cell.

Telophase II

  • Nuclear membranes form around chromosomes.

  • Spindle fibers break apart.

  • Cell undergoes cytokinesis.

  • End result: 4 haploid cells with a combination of chromosomes from both mother and father.

Mitosis vs. Meiosis

  • Mitosis:

    • Creates all the cells in your body (except sex cells).

    • Process of cell division that forms two new cells (daughter cells) each with the same number of chromosomes.

    • 1 cell division.

    • Asexual reproduction.

    • Results in diploid cells (2n).

    • No genetic diversity.

    • To repair damage body cells, growth

  • Meiosis:

    • Sex cells only (egg/sperm).

    • Process of cell division which four new cells are created- each with half the original number of chromosomes.

    • 2 cell divisions.

    • Sexual Reproduction.

    • Results in haploid cells (n).

    • Yes genetic diversity.

    • create sex cells that are needed for reproduction.

Crossing Over

  • When homologous pairs line up opposite of each other at the equator of the cell, parts of the chromatids can become twisted around each other.

  • This results in a new combination of genetic information.

  • Chromosomes transfer their genetic information and exchange it between each other.

  • This means that we receive a unique combination of our parents DNA, instead of our grandparent’s chromosomes.

Independent Assortment

  • Homologous pairs line up opposite each other at the equator of the cell.

  • It’s random which side of the equator the paternal and maternal chromosomes lie.

  • These pairs are separated, so one of each homologous pair ends up in the daughter cell.

  • This creates a large number of possible combinations of chromosomes in the daughter cells produced.

Non-Disjunction

  • Mistake during meiosis where the chromosomes aren't split evenly.

Gene Mutation

  • Diseases associated with mutation of a single nucleotide, are:

    • Sickle cell disease.

Hemoglobin

  • A protein in your red blood cells, it helps your red blood cells carry oxygen

Sickle Cell Trait

  • A condition where a person inherits one normal hemoglobin gene and one sickle cell gene from their parents.

  • People with the trait usually don’t have symptoms but can pass the gene to their children.

  • It’s different from sickle cell disease, which requires inheriting two sickle cell genes and causes more serious health problems.

Statistics

  • About 1 in 13 Black or African-American babies is born with sickle cell trait (SCT).

Relationship between Sickle Cell Traits and Malaria

  • People with sickle cell trait are partially protected against severe malaria because the sickle cell red blood cells make it difficult for the malaria parasite to grow and replicate.

  • People with sickle cell trait are generally healthy and don't experience the same symptoms as those with sickle cell disease, who have two copies of the sickle cell gene.

Mendelian Genetics

  • Heredity: The passing of traits from one generation to the next.

Gregor Mendel

  • Known as the father of genetics.

  • Born in 1822 in Austria.

  • Became a monk and worked in the monastery gardens.

  • Fascinated with inheritance of traits.

  • Mendel’s experiments with peas were able to show that genes are discrete units that keep their separate identities when passed from generation to generation.

  • Mendel used peas because they were easy to grow and had many traits that were easily distinguishable (color, shape, height, etc.).

Mendel's Laws

  • Mendel observed traits in his pea plants (7 to be exact).

  • Traits are distinguishing characteristics that are inherited.

  • Scientists knew that traits were inheritable (passed from one generation to the next), but they didn’t know how

  • In genetics, we refer to the mating of two organisms as a cross.

  • Mendel noticed that when he crossed a purebred, white-flowered pea plant with a purebred, purple-flowered pea plant, the resulting offspring looked like this:

  • Mendel drew three important conclusions which are known as Mendel’s laws:

    • Law of Segregation.

    • Law of Independent Assortment.

    • Law of Dominance.

Law of Segregation

  • Organisms inherit two copies of each gene, one from each parent.

  • Genes are pieces of DNA that provide instructions to make a certain protein.

  • Genes determine your traits (features or characteristics that are passed on to you - or inherited - from your parents).

Alleles

  • There can be different versions of genes called alleles.

  • You receive one from each parent.

  • Represented by letters (ex: Y for yellow color or y for green color in peas).

  • The alleles that an organism receives from its parents can be the same (homozygous).

  • Or… the two alleles might be different (heterozygous).

  • A genotype refers to an organism’s combination of alleles.

  • ex. BB, Bb, bb.

  • The physical characteristics, or traits, of an individual organism make up its phenotype.

  • ex. blue eyes, smooth peas, tall plant, brown fur.

  • As Mendel learned, one allele might be dominant over another.

  • A dominant allele is the allele that is expressed when two different alleles or two dominant alleles are present.

  • Dominant alleles are represented with uppercase letters.

  • ex. AA, Aa

  • A recessive allele is the allele that is only expressed when two copies are present.

  • ex. aa

  • Recessive alleles are represented with lowercase letters.

  • ex. Aa, aa

  • an organism’s genotype might be:

    • homozygous dominant (TT).

    • heterozygous (Tt).

    • homozygous recessive (tt).

Punnett Square

  • A Punnett square is used to show possible offspring of a genetic cross.

    • monohybrid- crosses one trait (4 boxes).

    • dihybrid- crosses two traits (16 boxes).

Practice

  • X/Y chromosomes – sexual development, puberty But also

  • The X chromosome has the genes for balding and color blindness

Baldness

  • Baldness (gene is on your X chromosome)

  • You don't inherit baldness from your father, but your mother

Color Blindness

  • Color blindness (gene is on your X chromosome)

Blood Type

  • A and B are dominant alleles

  • O is a recessive allele

Punnett squares for different blood type parent

  • Parents: Type A (Ao) × Type B (Bo)

  • Parents: Type AB (AB) × Type O (oo)

  • Parents: Type A (AA) × Type O (oo)

  • Parents: Type AB (AB) × Type AB (AB)

  • Parents: Two Type O parents

  • Parents: Type A (Ao) × Type AB (AB)

DNA and RNA

  • DNA and RNA are nucleic acids (1 of the 4 macromolecules we talked about before).

  • They both are made of nucleotides. (3 parts)

    • sugar (deoxyribose or ribose).

    • phosphate.

    • nitrogenous base.

      • adenine (A).

      • thymine (T) (DNA only).

      • guanine (G).

      • cytosine (C).

      • uracil (U) (RNA only).

DNA

  • DNA stores genetic information using its sequence of A’s, T’s, C’s, and G’s.

  • This genetic information is the instructions to make an organism's proteins.

  • You can think of DNA like a recipe book for proteins.

  • What: DNA= Deoxyribonucleic Acid

  • Structure:

    • DNA has a double helix shape.

    • It is double stranded (like a twisted ladder).

    • made of deoxyribose sugar.

    • nitrogenous bases: adenine, thymine, cytosine, guanine.

  • Where: in the nucleus of eukaryotes

  • Human DNA is 3 BILLION nucleotides long!!

RNA

  • RNA helps DNA to make proteins.

  • 3 types of RNA

    • mRNA- messenger RNA

    • rRNA- ribosomal RNA

    • tRNA- transfer RNA

  • Each type has its own job.

  • What: RNA= Ribonucleic Acid

  • Structure:

    • RNA is single stranded.

    • made of ribose sugar

    • nitrogenous bases: adenine, uracil, cytosine, guanine

  • Where: found in nucleus and cytoplasm

DNA Structure

  • Nucleotides link together to form long chains.

  • The nitrogenous bases match up in the middle to form a two stranded molecule

  • Sugar and phosphate are on the outside= backbone bases pairing in the middle 3 billion in humans

Base Pairing Rules

  • The nitrogenous bases pair up in a specific way.

    • A pairs with T.

    • C pairs with G.

    • In RNA: A pairs with U.

  • The pairs (and the two sides of DNA) are held together by hydrogen bonds.

DNA vs. RNA

  • DNA

    • Number of strands: 2

    • Type of sugar: deoxyribose

    • Nitrogenous bases: adenine, thymine, guanine, cytosine

    • Base pairing rules: A=T; C=G

  • RNA

    • Number of strands: 1

    • Type of sugar: ribose

    • Nitrogenous bases: adenine, uracil, guanine, cytosine

    • Base pairing rules: A=U; C=G

Discovery of DNA's Structure

  • James Watson and Francis Crick

  • Maurice Wilkins and Rosalind Franklin

DNA Replication

  • Whenever cells divide (mitosis), DNA must be copied.

  • DNA replication is the process of making a copy of DNA.

  • The DNA made during DNA replication is an exact copy of the original DNA.

  • This happens in S phase of interphase!!!

Rules

  • The bases in DNA match up in a certain way:

    • A pairs with T.

    • C pairs with G.

  • Therefore, DNA can be used as a template to make new DNA.

  • Since replication uses existing DNA as a template, it is semiconservative.

  • Semiconservative means that each DNA molecule consists of an original strand and a new strand.

  • Copying DNA requires many enzymes (proteins).

Enzymes and function

  • Helicase - separates DNA strands

  • DNA Polymerase - adds nucleotides and proofreads

  • Ligase - links new pieces of DNA.

Replication facts

  • It takes cells around 6-8 hours to replicate DNA.

  • Your cells have replicated trillions of times in your lifetime.

  • Mistakes do happen sometimes, but DNA polymerase fixes it most of the time.

  • Errors are limited to around 1 per 1 billion nucleotides.

Protein Synthesis

  • DNA contains instructions to make all of an organism's proteins.

  • RNA helps DNA make proteins.

  • This idea that DNA → RNA → Proteins is called the Central Dogma.

  • The central dogma explains how life is determined through DNA.

DNA Contains Genes

  • A section of DNA that codes for a protein is called a gene.

  • The gene is read, and the message is used to make a protein.

  • Proteins then determine traits such as eye color or dimples.

Protein Synthesis

  • Protein synthesis is the process of making proteins.

  • There are two steps:

    • Transcription- mRNA copies DNA instructions.

    • Translation- ribosomes uses mRNA to make proteins.

Transcription

  • Location: Nucleus.

  • Players involved: DNA and mRNA.

  • What happens:

    • DNA unwinds where the gene is.

    • RNA polymerase uses DNA as a template to make an mRNA copy (transcript).

    • Now the mRNA copy can leave the nucleus.

  • mRNA has codons- a sequence of 3 nucleotides that code for an amino acid (the building blocks of proteins) U A C G C U mRNA segment codon codon

  • You can think of codons like the words of the genetic code. You need to translate all of the words in order to get the message (protein).

Summary of different types of RNA

  • mRNA: carries DNA message as codons.

  • rRNA: makes up ribosomes.

  • tRNA: matches anti-codon to mRNA codon to bring the correct amino acid.

Step2: Translation

  • Location: ribosomes.

  • Players involved: mRNA, ribosome (rRNA), and tRNA.

  • What happens:

    • mRNA finds a ribosome and binds to it.

    • The mRNA codons are read by the tRNA.

    • tRNA brings in the right amino acid that matches the codon.

    • The amino acids link together to form a protein.

  • Each gene carries a series of coded instructions ('code words') for the synthesis of proteins.

  • Each 'code word' on the DNA is made up of three bases (three 'letters') in a certain sequence.

  • Each 'code word' - called a triplet - corresponds to a single amino acid in a protein.

  • The sequence of bases in DNA is therefore a series of coded instructions for the building up of amino acids into proteins.

  • The proteins then give the cell or organism a particular characteristic.

  • This relationship between DNA bases and amino acids is called the genetic code.

  • Sometimes changes will happen in the nucleotide sequence, this changes the amino acid sequence, and so changes the protein structure This is called a mutation!!!