Genetics 3.1 Genes 3.2 Chromosomes

Genetic Material All organisms need to undergo cell division in order to grow and to reproduce. During cell division, genetic material is duplicated and passed on from a parent cell to new daughter cells GENETICS: is the study of heredity and variation. It explains how living things inherit traits from their parent.

Most organisms store their genetic information in the form of the molecule DNA (deoxyribonucleic acid). DNA contains a lot of information, and can be very long. In order to keep it organized, the cell condenses DNA into chromosomes.

Chromosomes are found in the nucleus of eukaryotic cells. The size, shape, and number of chromosomes vary based on the species. Ex: Humans have 46 chromosomes in each of their body cells but dogs have 78, and fruit flies have 8.

Prokaryotic Chromosome Bacteria have 1 chromosome in their nucleoid region made of 1 circular DNA molecule. Their DNA is “naked” – not associated with proteins (such as histones) Remember some prokaryotic cells also have plasmids which are extra DNA molecules found in the cytoplasm. They are small, circular, naked and only contain a few genes.

Prokaryotic DNA

Eukaryotic Chromosome Too thin to be visible during interphase. During the division of nuclear material (mitosis or meiosis) the chromosome condense becoming shorter, fatter, and visible under the microscope Since DNA replication occurs during interphase, at the beginning of mitosis and meiosis eukaryotic chromosome are double stranded.

Eukaryotic Chromosomes

Eukaryotic Chromosomes There are at least 2 different types of chromosomes in a eukaryotic cell. Humans have 23 different types (and 2 of each type! – to give a total of 46)

What’s different about each type of chromosome? The size (the length of the DNA that comprises it) The position of the centromere holding together the sister chromatid strands Most importantly, the type of genes located on the chromosomes

Gene a segment of a DNA molecule that codes for a particular trait (codes for a protein!) found at a specific location on a chromosome. The sequence can be hundreds or thousands of nitrogen bases long.

Locus (Plural: loci) The location of gene on a chromosome.

Alleles various specific forms of a gene. Brown eyes and blue eyes are different alleles for the eye colour gene. If Jason has blue eyes and Ellen has brown eyes, the locus for these genes are at the same place on the same chromosome of each individual.

Alleles

Alleles Alleles differ from each other by one or a few bases only. Usually only one or a very small number of bases are different. Ex: Adenine might be present in a particular position in one sequence and cytosine in that position in another allele

Alleles Alleles differ from each other by one or a few bases only. Usually only one or a very small number of bases are different. Ex: adenine might present in a particular position in one sequence and cytosine that position in another allele.

Homologous Chromosomes Chromosomes of the same type. They have the same size, shape and sequence of genes in the same loci. However, they are not exactly the same because they likely come from different parents. Ex: You have two copies of chromosome #1. One came from your mom, the other from your dad

Homologous Chromosomes Each chromosome in a homologous pair of chromosomes may be referred to as a homolog If a pair of homologous chromosomes have the same type of allele for a gene, they are said to be homozygous. Ex: if they both have the allele for brown eyes.

Homologous Chromosomes If the alleles on the homologous chromosomes are different, they are heterozygous Ex: If one homolog has the allele for brown eyes and the other has the allele for blue eyes

Homologous Chromosomes

Homologous Chromosomes

Diploid vs Haploid Cells If the nucleus of a cell contains homologous chromosomes, i.e. 2 of every type of chromosome, then the cell is said to be diploid. Somatic cells (normal body cells) are diploid.

Diploid vs Haploid Cells If the nucleus of a cell only contains one of every type of chromosome (only 1 homolog), it is said to be haploid. Gametes (sex cells) are haploid.

Diploid vs Haploid Cells

Genome all the genetic information of an organism

The Human Genome Project This was a collaborative project amongst many scientists. Its purpose was to find the base sequences of the entire human genome. Began in 1990. Completed in 2003. While an entire genome was sequenced, Scientists are still interpreting the genes. Work continues to find variations in the sequence between different individuals (and different alleles)

Human Genome Project Analysis has shows that the vast majority of base sequences are shared by all humans, but there are also many single nucleotide polymorphisms which contribute to human diversity. Genomes for many other species have also been determined Comparisons between genomes of different species is key in understanding the evolutionary relationship and history of living organisms.

Mutations Mutations are random changes in DNA sequences. New alleles are formed from mutated sequences. Evolution is the result of mutation (and the natural selection of new alleles!)

Mutations A substitution mutation is when one base in the sequence is replaced by a different nitrogen base. Ex: if in a particular gene sequence, adenine was substituted for another base such as cytosine. phenylalanine proper mRNA sequence 5’ AGG CUG UUU GGA 3’ mutated sequence 5’ AGG CUG UUA GGA 3’ leucine

Mutations If the wrong nitrogen base was found in the sequence, it would result in a different codon and possibly a different amino acid in the protein. The new amino acid could cause the protein to fold differently affecting the function of the protein.

Mutations Mutations may be beneficial, neutral, or harmful Sometimes mutations can be lethal and cause death to the cell where the mutation occurs. If a mutation occurs in a somatic cell (body cell), it will be eliminated when the individual dies and will not be passed on to the next generation

Mutations i.e. If you develop a mutation in your skin cells causing skin cancer, it will not be passed on to the next generation. However, if the mutation occurs in a gamete (a sex cell used to create a new individual), it will be passed on to the offspring (the next generation)

Sickle Cell Anemia A common genetic disease that causes the production of a sickle celled shaped red blood cell, opposed to the normal biconcave shape. Effect: Blocks capillaries, less efficient at transporting O2 Symptoms: lack of O2  Physical weakness, heart, and kidney damage; can even lead to death

Sickle Cell Anemia Sickle-cell anemia is caused by a substitution mutation. For normal hemoglobin, on the DNA, the 6th codon on the coding strand should be GAG. The mutation causes GTG instead. This means the mRNA strand will read GUG which codes for valine instead of glutamic acid

Sickle-Cell Substitution Mutation

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Reproduction Organisms inherit genetic information from their parents via reproduction. There are 2 basic types of reproduction: asexual and sexual.

Asexual Reproduction Production of offspring (a cell or an organism) from a single parent The offspring are genetically identical to the parent

Cell division (which includes mitosis) is a form of asexual reproduction. It is what causes growth of the overall organism. Cloning is a form of asexual reproduction

Advantage of Asexual Reproduction: The parent cell/organism does not have to seek out a mate (conserves energy), perform mating rituals or posses specialized anatomy. Disadvantage: there is little genetic variation It is the most common form of reproduction amount unicellular organisms. Many multicellular organisms use it too (plants, fungi)

Binary Fission Occurs in bacteria; Similar to mitosis

Budding Occurs in yeast and some multicellular organisms such as hydra. The organism grows and extensions, a “bud”, that eventually breaks off the parent.

Spore Formation Occurs in bacteria and mold The parent organism produces smaller cells called “spores” that can detach from the parent, land in another area and grow

Vegetative Propagation Occurs in many plants such as strawberries The plant produces a long stem-like feature called a “runner” that can detach from the plant and grow roots easily. (Also called vegetative reproduction)

Fragmentation Occurs in algae, and some plants and animals A new organism is formed when part of the parent is broken off. Ex: when a starfish or earthworm is broken in half, 2 new organisms will grow.

Aphids In the spring female aphids can produce more female aphids that are essentially clones of themselves. In the fall, changes in their hormone levels causes them to produce males. Then male and female aphids can reproduce sexually.

Videos http://www.youtube.com/watch?v=jk2RJm5R BEk

Sexual Reproduction A form of reproduction in which individuals are produced from the fusion of two sex cells (gametes) The sex cells usually come from 2 different parent organisms

Sexual Reproduction Ie: Females produce egg cells, males produce sperm cells. When they combine, they form a fertilized egg called a zygote. We were all zygotes at one point.

The offspring of sexual reproduction are not genetically identical to either of its parents Offspring obtain half of their DNA from each of their 2 parents. Remember, even if an organism uses sexual reproduction to reproduce, the individuals will still undergo asexual reproduction to grow.

DISADVANTAGES Must have specialized organs to produce sex cells Must expend energy to find a suitable mate, and may also put oneself in danger from predators to make oneself visible to potential mates

ADVANTAGE Genetic variation!

GENETIC VARIATION Genetic Variation allows for evolution. If all the individuals of a species were genetically identical, when the environment changes, it can potentially wipe out all those individuals. But if a few individuals happen to possess different genes, genes that would allow them to potentially survive the environmental change, then life would perpetuate.