Exam 3 Bio Study Guide

Chromosome theory of inheritance

Chromosome theory of inheritance

states that genes are located on chromosomes, and that the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

Homologous chromosome

chromosomes that are similar in shape, size, and genetic content

Sex Linked gene

a gene that is located on either chromosome 

X linked gene

genes on the X chromosome  

• Recessive disorders are much more common in males than in females 

• have genes for many unrelated to sex  

• For a recessive __ trait to be expressed 

• A female needs two copies of the allele (homozygous)  

• A male needs only one copy of the allele (hemizygous)  

Y linked gene

genes on the Y chromosome

- have genes help determine sex  

Nondisjunction

pairs of homologous chromosomes do not separate normally during meiosis I or sister chromatids do not separate during meiosis I or sister chromatids do not separate during meiosis II 

• As a result, one gamete receives two of the same type of chromosome, and another gamete recieves no copy  

Aneuploidy

results from fertilization involving gametes in which nondisjunction occurred  

• Offspring with this condition have an abnormal number of a particular chromosome

Monosomic

a ___ zygote has only one copy of  a particular chromosome 

Trisomic

a ___ zygote has three copies of a particular chromsome

Polyploidy

a condition in which an organism has more than two complete sets of chromosomes 

• Triploidy (3n) is three sets of chromosomes 

• Tetraplody (4n) is four sets of chromosomes 

• Is common in plants but not in animals  

Deletion

removes a chromosomal segment 

Duplication

repeats a segment 

Inversion

reverses orientation of a segment within a chromosome

Translocation

moves a segment from one chromosome to another 

Character

distinct heritable features (such as flower color)

Trait

character variants (such as purple or white flowers)

True Breeding

plants that produce offspring of the same variety when they self-pollinate  

P generation

the true breeding parents

F1

the hybrid offspring of the P generation

F2 generation

produced when F1 individuals self-pollinate/cross pollinate with other F1 hybrids   

Law of Segregation

states that during gamete formation, each parent passes one of their two copies of a gene to their offspring at random  

• According to this law, only one of the two gene copies present in an organism is distributed to each gamete that it makes 

• The two alleles for a heritable character separate during gamete formation and end up in different gametes  

• Corresponds to the distribution of homologous chromosomes to different gametes in meiosis 

Allele

alternative versions of a gene  

• Two of these are inherited, one from each parent 

Dominant Allele

determines the organism’s appearance if two alleles at a locus differ 

Recessive Allele

has no noticeable effect on appearance  

Homozygous/ Homozygote

an organism with two identical alleles for a character is said to be ____ for the gene controlling that character 

Homozygous dominant

two copies of the dominant form of a gene (TT)  

Homozygous recessive

two copies of the recessive form of the gene (tt)  

Heterozygous/heterozygote

two different genes (Tt): an organism that has two different alleles for a gene is said to be _____ for the gene controlling that character  

• Aren't true breeding  

Phenotype

the physical appearance (tall or short)  

Genotype

the letters that represent genetic makeup (TT, Tt, tt)

Test Cross

breeding the individual with a recessive homozygote is called a ____ because it can reveal the genotype of that organism  

Monohybrid/monohybrid cross

the F1 offpspring produced in this cross were ____, individuals that are heterozygous for one character  

• A cross betwen such hetereozygotes is called a ____ 

Dihybrid/ dihybrid cross

produced by crossing two true breeding parents differing in two characters in the F1 generation, heterozygous for both characters 

• A cross between F1 ____, can determine whether two characters are transmitted to offspring as package or independently 

Law of independent assortment

states that each pair of alleles segretgates independently of any other pair during gamete formation  

• Only applies to genes on chromosomes that are not homologous, or those far apart on the same chromosome 

• Genes located near each other on the same chromosome tend to be  inherited together

Complete dominance.

one form is completely dominant or completely recessive (red OR white)  

• Occurs when phenotypes of the heterozygote and dominant homozygote are indsitinguishable  

Incomplete dominance

mix of two traits (red + white = maroon)  

• The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varietes  

Codominance

both traits are dominant, meaning you can see them simaltaneously (commonly seen with coloration of animals and the ABO blood type system) 

• Two dominant alleles affect the phenotype in separate, distinhuisable ways  

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus

Polygenetic inheritance

an additive effect of two or more genes on a single phenotype 

Pedigree

a family tree that conmtains a family’s history for a particular trait  

Carrier

heterzygous individuals who carry the recessive allele but are phenotypically normal 

Multifactorial disorder

characters influenced by genetic and environmental factors collectively  

Genes

The units of heredity and are made up of segments of DNA

Gametes

• The reproductive cells that allow genes to be passed down  

• Sperm or egg; contains a single set of chromosomes and is haploid (n) 

• Only type of human cells produced by meiosis rather than mitosis  

• Fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism 

Somatic Cell

the cells of the body except for gametes and their precursors  

• In humans have 23 pairs of chromosomes 

Locus

specific locations for each gene on the chromosome

Asexual Reproduction

reproduction in which a single individual passes gene to its offspring without the fusion of gametes 

Clone

a group of genetically identical individuals from the same parent, produced asexually  

Sexual reproduction

reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from two parents 

Karyotype

an ordered display of the pairs of chromosomes from a cell  

homologous chromosome

the two chromosomes in each pair 

• The chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited characters  

Sex chromosome

a package of DNA with part of/all of the genetic material  

• Determine the sex of the individual; called X and Y 

• Females have a homologous pair of X chromosomes (XX) 

• Males have one X and one Y chromosome 

Autosome

the remaining pairs of chromosomes aside from the sex chromosomes 

Diploid

(2n) an organism has two complete sets of chromosomes 

• 23 from the mother; 23 for the father; total of 46 

Haploid

an organism that has one set of unpaired chromosomes; 23n  

• Each set of 23 consists of 22 autosomes and a single sex chromosome 

Fertilization

the union of gametes (the sperm and the egg cell)  

• Zygote (egg after union) has one set of chromosomes from each parent and so is diploid  

• Zygote produces somatic cells by mitosis   

Meiosis

• Takes place in two sets of cell divisions, which result in 4 daughter cells each of which only have half as many chromosomes as the parent cell  

• Produce gametes 

• Results in one set of chromosomes in each gamete 

• This, when combined with fertilization, maintain chromosome number 

• Reduces the number of chromosomes sets from two (diploid) to one (hapoloid), producing cells that differ genetically from each other and from the parent cell  

• Produces 4 new haploid cells 

Meiosis I

• Prophase I: synapsis and crossing over 

• Homologous chromosomes physically connect and exchange genetic information  

• Two members of a homologous pair associate along their length, allele by allele 

• Metaphase I: alignment of homologous pairs; homologous pairs of chromosomes are positioned there in the first phase of this 

• Homologous pairs line up at the platem with one chromosome facing each pole 

• Microtobules from one pole are attatched to the kinetochore of one chromosome of each tetrad 

• Anaphase I: Separation of homologs 

• One chromosome moves toward each pole, guided by the  spindle apparatuus 

• Telophase I: at the beginning of this stage, each half of the cell has a haploid set of chromosomes 

• Each chromosome still consists of two sister chromatids 

• Cytokinesis usually occurs simultaneously, forming two haploid daughter cells  

Meiosis II

• Occurs in four phases: 

• Prophase II: 

• Spindle apparatus forms 

• Later in this stage chromosomes (each still comprised of two chromatids) move toward the metaphase plate 

• Metaphase II: the sister chromatids are arranged at theplate 

• Because of crossing over in in the first version of this stage, the two sister chromatids of each chromosome are no longer genetically identical 

• The kinetochores of sister chromatids attatch to microtubles extending from extending opposite poles 

• Anaphase II:  

• In this stage, the sister chromatids separate 

• The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles  

• Telophase II + cytokinesis  

• Nuclei form, and the chromosomes begin decondensing  

• At the end of meiosis, there are four daughter cells, each with a haploid set of unduplicated chromosomes 

• Each daughter cell is genetically distinct from the others and from the parent cell  

Chromosomes

Each one replicated consists of two identical sister chromatids 

Sister chromatid

identical copies of a chromosome that are joined together by a centromere 

Crossing Over

nonsister chromatids exchange DNA segments  

• Produces recombinant chromosomes- combine DNA inherited from each parent  

• Contributes to genetic variation by combining DNA, producing chromosomes with new combinations of maternal and paternal alleles 

Independent Assortment

one of the mechanisms that contributes to genetic variation 

• Homologous pairs of chromosomes orient randomly at metaphase I of meiosis 

• Each pair of chromosomes sorts maternal and paternal homologs into daughter cells independetly of the other pairs  

• Number of combinations possible when chromosomes assort independently into gametes is 2n 

Recombinant Chromosome

combine DNA inherited from each parent 

Random Fertilization

adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg) 

• Each zygote has a unique genetic identity  

Prophase I

Metaphase I

Anaphase I

Telophase

Meiosis II

Polymer

long molecule consisting of many buildings' blocks; composed of monomers  

Monomer

The subunit that serves as the building block of a polymer. 

Dehydration Synthesis

occurs when 2 monomers bond together through the loss of a water molecule 

Hydrolysis

polymers that are disassembled to monomers through the process of adding water   

Enzyme Section

speed up chemical reactions without being consumed in the reaction 

Polypeptide

A polymer of many amino acids linked together by peptide bonds. 

Amino Acid

are organic molecules with carboxyl and amino groups 

Protein

biologically functional molecule that consists of one or more polypeptides 

Peptide Bond

The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a dehydration reaction. 

Catalyst

A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction

Protein Structure

A protein’s structure determines its function 

• Have 4 levels of structure: 

• Primary: protein’s unique sequence of amino acids 

• Secondary: consists of coils and folds in the polypeptide chain  

• The result of hydrogen bonds between constituents' of the polypeptide backbone 

• Include the α helix and the β pleated sheet 

• Tertiary: the overall shape of a polypeptide 

• Determined by interactions among various side chains (R groups)  

• Quaternary Structure: arises when a protein consists of two or more polypeptide chains 

• Results from interactions between multiple polypeptide chains 

Denaturation

the loss of a protein’s native structure 

• Is biologically inactive 

Nucleic Acids

• 2 Types  

• DNA (Deoxyribonucleic Acid) 

• Provides directions for its own replication  

• Directs synthesis of messenger RNA (mRNA) ad, through mRNA, controls protein synthesis, a process called gene expression  

• Contains thymine  

• RNA (Ribonucleic Acid) 

• Contains uracil 

Polypeptide

molecules made up of nucleotides that are linked together by covalent bonds to form a chain 

Ribose

the sugar in RNA

Deoxyribose

the sugar in the DNA

Double Helix

formed by DNA molecules have two polynucleotides spiraling around an imaginary axis 

Carbohydrate

macromolecules are polysaccharides, polymers composed of many sugar building blocks 

Monosaccharide

The simplest carbohydrates; AKA simple sugars serve as major nutriets for cells and as raw materials for building molecules

Disaccharide

formed when a dehydration reaction occurs joins two monosaccharides 

Glycosidic Linkage

Positions determine the structure and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages 

Polysaccharide

the polymers of sugars, have storage and structural roles 

• The structure and function of a ____ are determined by its sugar monomers and the positions of its glycosidic linkages 

Starch

a storage polysaccharide of plants, consists entirely of glucose monomers 

• Plants store surplus as granules 

• Most animals have enzymes that can hydrolyze this, making glucose available as a nutrient 

Glycogen

is a storage polysaccharide in animals 

Lipid

• do not form true polymers 

• Has little to no affinity for water 

• Are hydrophobic because they mostly consist of hydrocarbons, which form nonpolar covalent bonds 

• Most biologically important forms are fats, phospholipids, and steroids 

Fat

type of lipid; constructed from two types of smaller molecules: glycerol and fatty acids 

• separate from water because water molecules hydrogen bond to each other and exclude the fats 

• Primary function is energy storage 

Fatty Acid

consists of a carboxyl group attached to a long carbon skeleton 

• Two tails tails are hydrophobic; the phosphate group and its attachments form a hydrophilic head 

Saturated fatty acid

have the maximum number of hydrogen atoms possible and no double bonds 

Unsaturated fatty acid

have one or more double bonds 

Phospholipid

two fatty acids and a phosphate group are attached to glycerol  

• are major constituents of cell membranes 

• When are added to water, they self- assemble into a bilayer, with the hydrophobic tails pointing toward the interior  

• This feature results in the bilayer arrangement found in cell membranes 

• bilayer forms a boundary between a cell and its external environment