Genetics

4.1  The Nature of Heredity

Heredity: The passing of traits from parents to offspring

Genetics:

Deoxybronucleic Acid (DNA):A molecule that carries genetic information in cells

Gene: A segment of a DNA molecule that codes for a particular trait; found at a specific location on a chromosome

Locus: The location of a gene on a chromosome

Polyploid: Having more than two sets of chromosomes; many plants are polyploids 

Asexual reproduction: The production of offspring from a single parent; the genetic makeup of the offspring is identical to that of the parent

Sexual Reproduction: The production of offspring from the fusion of two sex cells (usually from two different parents); the genetic makeup of the offspring is different from that of either parent

Summuray:

•A fundamental aspect of reproduction is the passing on of genetic information from one generation to the next. 

• Genetic information is stored in DNA molecules within the chromosomes of cells. • Portions of the DNA molecule, called genes, carry heritable information and are found at distinct locations on a chromosome. 

• Chromosome number, shape, and size vary from species to species.

 • Asexual reproduction results in offspring that are genetically identical to their single parent. 

• Sexual reproduction results in offspring that are genetically variable. Offspring inherit half of their genetic information from each of two parents.

4.2 Asexual Reproduction Copies and Clones

Fragmentation: A method of asexual reproduction in which a piece or body fragment of the parent organism develops into a mature individual

Mitosis:The process by which a eukaryotic cell divides the genetic material in its nucleus into two new identical nuclei 

Interphase: The portion of the cell cycle between mitotic divisions when the genetic material (in the form of chromatin) is duplicated 

Chromatin: The tangled strands of DNA and protein within a eukaryotic nucleus Sister chromatid: The identical copy of a single chromosome that remains attached to the original chromosome at the centromere

Cytokinesis: The process in which a eukaryotic cell divides its cytoplasm into two new daughter cells

Cloning: The process of producing one individual that is genetically identical to another, using a single cell or tissue 

Biotechnology: The use and modification of organisms for applications in engineering, industry, and medicine

Genetically Modified Organism: An organism in which the genetic material has been altered using genetic engineering techniques

4.2 Summary

• Asexual reproduction results in offspring that are genetically identical to a single parent. 

• Cell division produces two daughter cells that are genetically identical to each other and to the original parent cell.

 • Clones have little or no genetic variability. • Mammals have been cloned from adult cells, but only with limited success.

 • Applications of biotechnology include the production of valuable pharmaceutical and commercial products, high-quality plants and livestock, and prize individual animals. 

• Cloned plants and animals are more vulnerable to changes in the environment and new diseases than are populations that exhibit genetic variability.

 • Cloning may prove valuable in the fight to protect endangered species.

4.3 Sexual Reproduction (Adding Variety)

Gamete: A sex cell; includes sperm cells in males and egg cells in females Fertilization: The formation of a zygote by the joining together, or fusion, of two gametes 

Zygote: A cell produced by the fusion of two gametes

Meiosis: A two-stage cell division in which the resulting daughter cells have half the number of chromosomes as the parent cell; results in the formation of gametes or spores

Homologous Chromosomes: Matching pairs of chromosomes, similar in size and carrying information for the same genes.

Tetrad: a pair of homologous chromosomes, each with two sister chromatids Synapsis: The physical pairing up of homologous chromosomes during prophase I of meiosis

Crossing Over: The exchange of chromosome segments between homologous pairs during synapsis

Gametogenesis: The production of gametes (sex cells) in animals Spermatogenesis: The production of mature sperm cells 

Oogenesis the production of mature egg cells

Karyotype: The chromosomes of an individual that have been sorted and arranged according to size and type

Sex Chromosomes: Chromosomes that differ in males and females of the same species; the combination of sex chromosomes determines the sex of the offspring

Autosomes: Non-sex chromosomes

4.3 Summary

• Sexual reproduction produces genetically variable offspring by combining the genetic information from two parents.

 • During meiosis I, chromosomes exchange genetic information, known as crossing over, during prophase I.

 • Homologous chromosomes are assorted independently of other pairs. 

• The formation of genetically variable sex cells in meiosis II is called gametogenesis.

 • There are many different sex-determination systems in living things. 

• Mammals have X and Y sex chromosomes and use an X X/ X Y system for female/ male sex determination.

4.4 Abnormal Meiosis and / or fertilization

:Non-disjunction: The failure of homologous chromosomes to move to opposite poles of the cell during meiosis; results in an abnormal number of chromosomes in the daughter cells

Trisomy: A chromosomal abnormality in which there are three homologous chromosomes in place of a homologous pair 

Monosomy: A chromosomal abnormality in which there is a single chromosome in place of a homologous pair

Down syndrome: A chromosomal abnormality in which an individual has three copies of chromosome number 21; also referred to as trisomy 21

Prenatal Testing: Testing for a genetic order that occurs prior to birth

Turner syndrome: One X and no Y sex chromosome. Approximately 1:2500 female births. Female in appearance but do not mature sexually and are sterile. Most Turner syndrome fetuses are miscarried before the 20th week of pregnancy.

Klinefelter syndrome: Two X and one Y sex chromosome. Approximately 1:500 male births. Males are usually sterile and exhibit some feminine body characteristics, but severity varies.

Patau syndrome: Trisomy of chromosome 13. Approximately 1:25 000 live births. Many serious developmental problems, including brain, kidney, and heart defects. Children rarely live more than a few months.

Edwards syndrome: Trisomy of chromosome 18. Approximately 1:6000 live births. Many organ system defects. Very low survival rate. Most fetuses die before birth. Average life expectancy of live-born infants is less than one month.

4.4 Summuray

• Errors in meiosis, including non-disjunction, can result in abnormal numbers of chromosomes and can cause serious genetic disorders. 

• Karyotypes can be used to evaluate chromosome numbers and diagnose genetic disorders.

 • Prenatal testing can be used to determine the likelihood of certain genetic disorders.

 • Assisted reproductive technologies may be used when a couple is infertile in order to enhance their chances of conceiving a child. 

• There are many applications of reproductive technologies in agriculture, industry, and wildlife conservation. 

• The use of many reproductive technologies is highly controversial.

4.5 Cytoplasmic Inheritance

Maternal Inheritance: A type of inheritance in which a zygote formed from two gametes inherits cytoplasmic DNA from only the female gamete

Paternal Inheritance: A type of inheritance in which a zygote formed from two gametes inherits cytoplasmic DNA from only the male gamete

Horizontal Gene Transfer: The transfer of genetic information from one species into a different species

ENDOSYBIOIC THEORY: The mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). 

4.5 Summary

• Mitochondria and chloroplasts are organelles within the cytoplasm that contain their own genetic material.

 • The genes in mitochondria and chloroplasts provide information necessary for performing cellular respiration and photosynthesis.

 • The genetic information in mitochondria and chloroplasts is usually inherited maternally.

 • The combination of genetic variation within organelles and the random assortment of organelles into daughter cells can produce genetic variation within the cells of individuals.

 • Some observable characteristics and genetic disorders are inherited through these cytoplasmic sources of DNA.

 • Horizontal gene transfer can result in one organism exhibiting a characteristic of an entirely different organism.

Chapter 5

Trait: trait a particular version of a characteristic that is inherited, such as hair colour or blood type

True - Breeding Organism: organism an organism that produces offspring that are genetically identical for one or more traits when self- pollinated or when crossed with another true-breeding organism for the same traits

Hybrid: the offspring of two different true- breeding plants

Cross: cross the successful mating of two organisms from distinct genetic lines

P Generation: the parent plants used in a cross

F1 Generation: generation the offspring of a P-generation cross

Monohybrid: the offspring of two different true-breeding plants that differ in only one characteristic

Monhybrid Cross:a cross designed to study the inheritance of only one trait

F2 Generation: generation offspring of an F1 generation cross

Law of Segregation: a scientific law stating that (1) organisms inherit two copies of genes, one from each parent, and (2) organisms donate only one copy of each gene to to their gametes because the genes separate during gamete formation

Allele: a specific form of a gene

Homozygous: describes an individual that carries two of the same alleles for a given characteristic

Heterozygous: describes an individual that carries two different alleles for a given characteristic

Genotype: the genetic makeup of an individual

Phenotype: an individual's outward appearance with respect to a specific characteristic

Dominat Allele: the allele that, if present, is always expressed

Recessive Allele: the allele that is expressed only if it is not in the presence of the dominant allele, that is, if the individual is homozygous for the recessive allele

Punett Squares: a diagram that summarizes every possible combination of each allele from each parent; a tool for determining the probability of a single offspring having a particular genotype

Probabilty: the likelihood that an outcome will occur if it is a matter of chance

Test Cross: a cross used to determine the genotype of an individual expressing a dominant trait

5.1 Summary: 

• Gregor Mendel studied heredity in pea plants. He was the first person to

successfully record and quantify heredity data.

• Genes have alternate forms known as alleles. Individuals have two alleles for

each gene.

• The two alleles are found at specific matching locations on homologous

chromosomes.

• Each parent passes on to its offspring only one of its two alleles for each gene.

This is called the law ofsegregation.

• Some alleles are dominant, while others are recessive. Dominant alleles are

always expressed in the phenotype, but recessive alleles do not show up unless

they are the only type of allele present in the genotype.

• A Punnett square is a tool that can be used to illustrate how alleles are

distributed from parent to offspring and to predict the frequency of

phenotypes and genotypes within a set of offspring.

Complete Dominance: a situation where an allele will determine the phenotype,

regardless of the presence of another allele

Incomplete Dominance: a situation where neither allele dominates the other and both have an influence on the individual; results in partial expression of both traits

Codominance: a situation where both alleles are expressed fully to produce offspring with a third phenotype

5.2 Summary 

Alleles that determine the phenotype regardless ofthe presence of other

alleles follow a pattern ofinheritance called complete dominance.

• A heterozygous individual with an intermediate phenotype between

the phenotypes ofthe two homozygous individuals follows a pattern of

inheritance called incomplete dominance.

• Co-dominance occurs when both alleles are fully expressed. Type A) B blood is

an example of co-dominance.

• Blood type is an example of a gene with multiple alleles. The three blood type

alleles are IA), IB, and i. Different combinations ofthe three alleles produce type

A), type B, type A)B, and type O blood.

Pedigree: a diagram of an individual's ancestors used in human genetics to

analyze the Mendelian inheritance of a certain trait; also used for selective breeding of plants and animals

Autosomal Inheritance: inheritance of alleles located on autosomal (non-sex) chromosomes

Sex-Linked: describes an allele that is found on one of the sex chromosomes,

X or Y, and when passed on to offspring is expressed

X-linked: phenotypic expression of an allele that is found on the X chromosome

Y-linked: phenotypic expression of an allele that is found on the Y chromosome

5.3 Summary 

• Pedigree charts are visual representations of a family tree that can be used to

follow the inheritance of a trait.

• If an allele is located on an autosome, or a non-sex chromosome, it is

transmitted through autosomal inheritance.

• Sex-linked inheritance occurs when a recessive allele is found on the X or Y

chromosome and that chromosome is passed on to the offspring.

• In X-linked inheritance, the sexes exhibit different phenotypic ratios. More

males than females will express the recessive phenotype, but more females are

carriers of the recessive X-linked allele.

• In Y-linked inheritance, traits are controlled by single alleles passed on from

fathers to sons on the Y chromosome.

Dihybrid Cross: a cross that involves two genes, each consisting of heterozygous alleles

Law of independent assortment: if genes are located on separate chromosomes,

they will be inherited independently of one another

Product Law: the probability of two independent random events both

occurring is the product of the individual probabilities of the events

Continous Variation: when the product of one gene is affected by the product of another gene, the gene products may be additive, or one product may negate another product

Addictive Allele: an allele that has a partial influence on a phenotype

5.7 Summary 

• Dihybrid crosses are crosses between individuals who differ in two pairs of

alleles; ifindividuals are heterozygous for both alleles, the phenotype ratio of

the offspring is 9:3:3:1.

• Mendel's law of independent assortment states that alleles of different genes

separate into gametes independently of each other.

• The probability of two independent events both occurring may be calculated

using the product law.

• Punnett square ratios are one way to show probability.

• Discontinous variation occurs when a trait is either expressed or not. There is

no in-between trait.

• Continuous variation occurs in nature when the expression of a characteristic

is the sum ofthe expression of all alleles involved.

Chapter 6

Nuclien: the original name given to DNA when it was discovered in the nucleus of cells by Friedrich Miescher in 1869

Nucleotide: the repeating unit in DNA; it comprises a deoxyribose sugar, a

phosphate group, and one of the four nitrogenous bases

X-ray crystallography: a technique in which a pure substance is subjected to X-rays; the pattern in which the X-rays bend and spread helps reveal the structure of the pure substance

Scientific Model: a simplified representation of a concept; can be tangible or conceptual

Complementary Base Pairing: pairing of the nitrogenous base of one strand of DNA with the nitrogenous base of another strand; adenine (A.) pairs with thymine (T), and guanine (G) pairs with cytosine (C)

6.1 Summary

 • Deoxyribonucleic acid (DNA) stores and transmits genetic information from

parent to offspring.

• DNA is made up of repeating nucleotides. Each nucleotide consists of a sugar,

a phosphate group, and a nitrogenous base.

• DNA has four nitrogenous bases: thymine (T), cytosine (C), adenine (A.), and

guanine (G).

• Thymine (T) and adenine (A.) are complementary bases. Guanine (G) and

cytosine (C) are complementary bases.

• James Watson and Francis Crick determined the structure of DNA. DNA

consists of two strandsthat run in opposite directions. Each strand is made up

of alternating phosphate and sugar molecules with nitrogenous bases attached

to the backbone.

Point Mutation: a small-scale change in the nitrogenous base sequence of a DNA;

the mutation may be beneficial, harmful, or neutral (having no effect on the organism)

Chromosome Mutation: an error that involves an entire chromosome or a large part of a chromosome

Spontaneous Mutation: a mutation that is not caused by any outside factors; it occurs randomly

Induced Mutation: a mutation that occurs because of exposure to an outside factor; second-hand smoke increases the chance of developing lung cancer

Antibiotic Resistance: describes strains of bacteria that are no longer susceptible to the effects of antibiotics; are sometimes called “superbugs” and are prevalent in hospital settings

6.2 Summary 

• A mutation is change in the genetic code of an allele.

• Examples of point mutations are base-pair substitutions, insertions, and

deletions. All result in a different protein being built by ribosomes.

• Lactose intolerance is the inability to digest lactose. Conversely, lactose

tolerance is the ability to digest lactose. Lactose tolerance is the result of a

mutation.

• Bacteria have developed antibiotic resistance due to mutations including those

in the gene that directs the shapes of cell wall building-block molecules.

• Transposons are sequences of DNA that can move along and between

chromosomes, possibly causing a change in an organism's phenotype.

Restriction enzymes:a molecule that has the ability to cut DNA at a specific site;

different restriction enzymes recognize and cut different sites

Recombination DNA: a fragment of DNA consisting of nucleotide sequences from at least two different sources

6.4 Summary 

• Genetic engineers can cut a gene from the genome of one organism and insert

it into the genome of a different organism, where it is expressed.

• Restriction enzymes are chemicalscissors that are able to cut out a gene

fragment from a DNA source.

• Plasmids are circular pieces of DNA that are able to exit and enter bacteria

cells and can be used to introduce new genes into an organism.

• Recombinant DNA technology uses plasmids and restriction enzymes to

produce organisms with new characteristics.

• The agriculture, health, and manufacturing industries use recombinant DNA

technology to increase disease resistance in crops and improve nutrition in

foods.

• Recombinant DNA spider silk is a product that one day may be used in

numerous applications as an alternative material.

• Bt corn has a gene that codes for a pesticide embedded within its genome. The use of Bt corn allows farmers to use less pesticides in cornfields.