GENETICS The study of heredity and variation in organisms
Inherited traits Passed from one generation to the next. They are encoded by DNA. Examples: Eye color Left- or right-handedness Butterfly wing patterns Animal fur color Acquired traits Develop or occur after an organism is born. They occur in response to environmental factors such as stress, overall health, nutritional choices, and chemical exposure. They are not a result of the organism s genetic code. Examples: Straightened teeth from wearing braces The loss of a limb in an accident
DNA A string-like molecule that stores the information needed to build an organism from one cell all the way up to trillions of cells. DNA = deoxyribonucleic acid Stored in the nucleus of nearly every cell in the body
Individual DNA strings are called chromosomes There are 23 different chromosomes in the human genome Each chromosome has two copies, so human cells are called diploid
1 chromosome from mom and 1 from dad Because the pairs are nearly identical, they are called homologous A karyotype is an image where all the chromosomes have been lined up in their pairs
DNA sometimes winds up and condenses making distinct chromosomes visible under a microscope
Sex Chromosomes Females have two homologous X-chromosomes
MOM X X DAD X XX XX Y XY XY Males have only one X-chromosome and a Y-chromosome
DNA and Protein DNA contains the instructions to make proteins ONLY Each chromosome has thousands of segments that each encode a single protein. Proteins are important structural parts of the body, hair, fingernails, cartilage
DNA and Protein enzymes and hormones are proteins that regulate cell functions (chemical messengers). e.g. the SRY gene encodes the SRY protein also known as the testis determining factor
The SRY gene is located on the Y-chromosome Around the 6 th week, the gene starts making SRY protein, which turn on other genes which produce other proteins, such as testosterone a hormone which stimulates the development of male sex organs If this gene fails, the fetus will develop into a female despite having the y-chromosome
CELL DIVISION You begin as a single cell and grow to ~40 trillion cells This is accomplished by cell division. Every time a cell divides, all of the DNA must be replicated and packaged into the two daughter cells
The 1 st 8 weeks of development The embryo grows and develops through cell division
2 Types of Cell Division: 1) MITOSIS: the division of the genetic material and the other contents of the nucleus into two complete and separate sets Regular (autosomal) cells
Mitosis is needed for: Growth Maintenance Repair The daughter cells must have the correct genetic information The DNA of the parent cell must be replicated accurately One complete set of chromosomes must be divided into each of the new nuclei
Mitosis DNA replicates Chromosomes align along the centre Chromosomes separate to opposite ends Cell Divides
Cancer In your body ~150 billion cell divisions happen each day Specific proteins in cells act as start or stop signals for cell division When these control mechanisms are disrupted resulting in rapid, uncontrolled cell division is causes a variety of diseases collectively termed CANCER.
The mass of dysfunctional cells is called a TUMOUR
2) MEIOSIS The formation of eggs (ova) and sperm in the ovaries and testes through cell division is called MEIOSIS.
DNA replicates Meiosis Cell division Homologous Chromosomes pair up Crossing over occurs (random exchange of DNA segments) Separation of chromosomes Another cell division to form gametes Gametes: egg (ovum) or sperm. They are haploid (only one copy of DNA)
Fertilization Two gametes (sperm and egg) join to form a diploid zygote, which develops into an embryo and then a fetus The fetus gets one copy of all 23 chromosomes from the sperm and one copy from the egg
Heredity & Variation
For 1000 s of years humans have realized that parents pass on traits to offspring SELECTIVE BREEDING uses this idea
GREGOR MENDEL S EXPERIMENTS
Mendel, an Austrian monk, published his work on pea plant inheritance in 1860s but it was ignored until 1900 He studied 7 traits that were expressed each in two easily distinguishable forms Before he began he chose plants that, when they selfpollinated, produced that same traits generation after generation (i.e. they were true-breeding)
Each trait he studied had a dominant and recessive allele. Alleles are different varieties of the same gene. A gene is a segment of DNA that controls a single trait. Explain the cross to the right.
PHENOTYPES AND GENOTYPES Alleles are different versions of the same gene
Phenotype - The physical trait expressed in the individual Genotype - The alleles present in the individual s DNA
We use Punnet squares to determine the probability of genotypes and phenotypes in offspring
USING PUNNET SQUARES
When an individual has two different alleles (e.g. Aa) for a trait, they are called a HETEROZYGOTE When an individual has two copies of the same allele (e.g. AA or aa), they are called a HOMOZYGOTE
TRAITS ENCODED BY THE X-CHROMOSOME e.g. Colour-blindness
Normal colour vision Red-green colour Blind Left Right Left Right 25 29 25 spots
Normal colour vision Red-green colour Blind Left Right Left Right 45 56 Spots 56
Normal colour vision Red-green colour Blind Left Right Left Right 6 8 Spots Spots
SEX-LINKED INHERITANCE Traits found on the sex chromosomes x-linked y-linked A common x-linked trait in humans red-green colour blindness
More Practice: p. 104
DNA S 3D STRUCTURE No, Timmy!! the nitrogenous base is linked to the 1 carbon
DNA (deoxyribonucleic acid) contains genetic information and is located in the nucleus of nearly every cell in the human body. DNA is made up of units called NUCLEOTIDES
Nucleotides are made up of Sugar (deoxyribose) & phosphates that link together to form a backbone Nitrogen BASE PAIRS
Factoids: Human DNA is 3 billion base pairs and about 2 m in length. 50% of the genes found in humans are also found in bananas We have 65% genetic similarity to fruit flies -
There are 4 different nitrogen bases that link together The sequence of the bases constitute the information stored by the DNA molecule (ribose)
Adenine (A) fits together with thymine (T) Guanine (G) fits together with cytosine (C) DNA is made up of two COMPLEMENTARY strands
Complementary strands that are joined naturally wind into a DOUBLE HELIX structure
Hydrogen Bonds The bases are held together by hydrogen bonds Electrons in 1 atom are weakly attracted to another atom
ROSALIND FRANKLIN In the 1950s, she used x-ray crystallography to study DNA s structure
Franklin concluded that DNA must have a HELICAL structure...and that the sugarphosphate backbone was located on the outside
WATSON AND CRICK In 1953, James Watson and Francis Crick Combined the experimental evidence into a 3D model that is now the accepted structure of DNA
DNA REPLICATION Every time a cell divides (mitosis), all of the DNA must be replicated. Enzymes unwind and separate the two strands. Other enzymes bring freefloating complementary nucleotides and attach them to each strand. The result is two identical strands.
THE HUMAN GENOME The word GENOME refers to the sum of all the DNA contained in the nucleus of each cell of an organism The human genome has about 3 billion base pairs and 20 25 thousand genes This includes large regions that don t appear to code for anything at all
SEQUENCING GENOMES The first organism (a virus) was sequenced in 1977 Faster methods have since been developed
SEQUENCING GENOMES In 2003, an international team of researchers completed the HUMAN GENOME PROJECT, in which they sequenced the entire human genome
GENE EXPRESSION DNA contains the information needed to build specific proteins Each gene is a segment of DNA that encodes a single protein.
GENE EXPRESSION The sequence of DNA has to be translated into a sequence of amino acids the building blocks of proteins
Transcription During gene expression, DNA is copied into a molecule called RNA using amino acids The RNA then moves out of the nucleus into the cytoplasm
In a gene, the base pairs are divided into threes called base triplets or CODONS. Each codon corresponds to an amino acid
Translation To make the proteins needed by a cell, it must translate the codons into a series of amino acids The nucleotides in the RNA are translated into proteins in the cytoplasm Some codons are stop signals to end protein manufacture
The genetic code is continuous, no spaces, or punctuation some codons do not code for amino acids, they are stop signals for protein building Genetic code is redundant, some codons will make the same amino acid
P 114: #33, 34 Practice if needed
Gene Expression The condition, called diprosopus, is also seen in humans is apparently caused by an overexpression of the sonic hedgehog gene, a control gene in patterning many parts of the body. larger-than-normal quantities can widen one face into two.
Proteins can turn genes off and on The patchy colours of the cat are the result of pigmentation genes in different areas of the skin.
Belgian Blue Cattle a naturally occurring mutation of the gene for myostatin, a protein that regulates muscle growth. This mutation results in accelerated lean muscle growth.
from the Isle of Man, with a naturally occurring mutation that shortens the tail. Manx Cat
Black jaguars have at least one copy of a mutant MC1R sequence allele
Red hair appears in people with two copies of a recessive gene on chromosome 16 which causes a change in the MC1R protein. Red Hair
1 amino acid is changed which causes red hair
CAUSES OF MUTATIONS Some chemicals called MUTAGENS
SPONTANEOUS MUTATIONS Not caused by external agents, but rather occur naturally One cause is incorrect base pairing by DNA polymerase during DNA replication
Radiation High-energy (ionizing) radiation Particles (alpha and beta radiation) Electromagnetic Radiation (EMR) (Gamma radiation, X- rays, Ultraviolet Radiation)
Mutations caused by ultraviolet radiation can result in melanoma (a type of skin cancer)
TYPES OF MUTATIONS POINT MUTATION: the substitution of a single nucleotide for another GTT CAT TTG ACT CCC GAA GAA val his leu thr pro glu glu GTT CAT TTG ACC CCC GAA GAA val his leu thr pro glu glu
Harmful mutation GTT CAC TTG ACA CCC GAA GAA Val his leu thr pro glu glu GTT CAC TTG ACA CCC GTA GAA Val his leu thr pro val glu
BRCA Genes BRCA1 and BRCA2 are human genes that produce tumor suppressor proteins. These proteins help repair damaged DNA Everyone has these genes
Men with BRCA1 or BRCA2 mutations have a higher risk of prostate cancer. Men and women with BRCA1 or BRCA2 mutations may be at increased risk of pancreatic cancer
Mutation Example 4: An original mrna sequence with the amino acids they encode FRAMESHIFT MUTATION An addition or deletion of a nucleotide that causes the codons to be read in an alternate pattern Original strand: Replicated: ATG GGA GTT CA TGG GAG TTC A The 1 st base is deleted which causes the other bases to shift one space left in the order
GENETIC DISORDERS IN HUMANS
Nondisjunction Caused when chromosomes do not separate properly during meiosis Produces gametes with too many or too few chromosomes Trisomy is when a cell has 3 copies of a chromosome
Most autosomal (non-sex chromosomes) trisomies are lethal
Nondisjunction: trisomy of chromosome 18
P 121
TRACING GENETIC DISEASES -using pedigree charts
Autosomal non-sex chromosome Recessive Must be homozygous to be expressed in the phenotyp How can we tell?
Autosomal Dominant How can we tell?
https://www.youtube.com/watch?v=-ho6hmh1kbm
X-linked recessive How can we tell?
A CARRIER is an individual who possesses a recessive allele, but doesn t express the phenotype e.g. the allele for hemophilia is recessive and X-linked. Only females can be carriers, because they have two X chromosomes, while males only have one. CARRIER GENOTYPE: X H X h PHENOTYPE: NORMAL (NON-HEMOPHELIAC)
Are mutations always harmful?
Mutations provide variations needed for evolution to occur.
Bacteria evolve to be resistant to antibiotics because of variations caused by mutation
GENETIC FINGERPRINTING A method the genetically distinguish between two individuals of the same species It is not practical to sequence the entire DNA sample (3 x 10 9 base pairs in the human genome) APPLICATIONS: Forensic science (DNA from skin, hair, saliva, blood semen) Identification of remains Paternity/Maternity testing Organ donor matching Phylogenetics (relatedness between species) Tracing lineages and migrations in the past It is not literally a fingerprint
https://www3.nationalgeographic.com/genographic/
GENE THERAPY Can be used to replace defective or missing genes The gene is isolated in a healthy individual and removed using enzymes A vector (such as a virus) is used to insert the gene
Genetic Therapy for Colourblindness
GENETIC SCREENING People can be tested for certain alleles from a blood, saliva or skin sample Fetuses can be tested by collecting cells by amniocentesis