AP Biology Unit 5

Interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases

Prophase I

The first phase of meiosis I. the replicated chromosomes condense, homologous chromsomes pair up, crossing over occurs between homologous chromosomes, the spindle is formed, and the nuclear envelope breaks apart into vesicles. the longest phase of meiosis.

Metaphase I

Assembly of the spindle apparatus is completed, and the chromosome pairs (bivalents) line up across the center of the cell between the two centrioles.

Anaphase I

homologous chromosomes are separated (the bivalent is split) and pulled to opposite sides of the cell.

Telophase I

2 haploid daughter cells formed each with only one chromosome from each homologous pair

Prophase II

The first phase of meiosis II in which spindle fibers begin to reappear and centrioles move to opposite poles

Metaphase II

chromosomes line up along the equatorial plan

Anaphase II

centromere splits, sister chromatids are pulled to opposite poles by the spindle fibers

Telophase II

A nuclear envelope forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells, each with a haploid set of chromosomes.

Chromosomes

structures made of one DNA molecule and proteins

Somatic Cells

body cells

Gametes

reproductive cells

Chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes.

Centromere

Point on a chromosome by which it is attached to a spindle fiber during cell division.

Sister Chromatids

Identical copies of a chromosome; full sets of these are created during the S subphase of interphase.

Mitosis

division of the nucleus into two identical daughter nuclei containing the same number of chromosomes

Cytokinesis

division of the cytoplasm to form two separate daughter cells(immediately after mitosis, meiosis I, or meiosis II.)

Meiosis

Cell division producing haploid gametes

Mitotic (M) Phase

mitosis and cytokinesis

Mitosis: Cell separates and divides chromosomes

Cytokines: Cell divides cytoplasm and organelles.

G1 phase

Cell grows, duplicates organelles, and gathers materials for DNA replication.

S phase

DNA replication occurs

G2 Phase

growth and final preparation for division, nucleus well defined.

Mitotic Spindle

a structure made of microtubules that controls chromosome movement during mitosis

Centrosome

A structure that functions as the microtubule organizing center and is important during cell division, has two centrioles.

Kinetochore

A structure within the centromere containing the motor protein dynein. Moves the chromosomes apart during anaphase.

Diploid

2 sets of chromosomes

Haploid

having a single set of unpaired chromosomes

Fertilization

Fusion of an egg and sperm cell

Zygote

diploid fertilized egg

Crossing Over

exchange of genetic material between homologous chromosomes during prophase I of meiosis

Tetrad

structure containing 4 chromatids that forms when homologs pair during meiosis

True Breeding

have identical alleles of a given gene/ homozygous

Hybridization

The cross of two true-breeding parents. (BB x bb)

P generation

Parental Generation

Alleles

Different forms of a gene

Punnet Square

A chart that shows all the possible combinations of alleles that can result from a genetic cross

Homozygous

having two identical alleles for a trait. BB or bb

Heterozygous

having two different alleles for a trait. Bb

Phenotype

physical characteristics of an organism (blue eyes)

Genotype

genetic makeup of an organism (bb)

Mendel's Law of Segregation

Alleles segregate from one another during the formation of gametes. (due to independent assortment)

Monohybrid

A cross between individuals that involves one pair of contrasting traits

Dihybrid Cross

a cross between individuals that involves two pairs of contrasting traits

law of Independent Assortment

non-linked genes separate into gametes independent of one another in meiosis

Codominance

A condition in which both proteins produced by the alleles for a gene are fully expressed. (spots/stripes)

Incomplete Dominance

Cases in which one allele is not completely dominant over another. The two proteins produced by the alleles mix. (blended colors)

Multiple Alleles

A gene that has more than two alleles, like blood type (A,B,O)

polygenetic inheritance

many genes are involved in specifying traits that exhibit continuous variation (ie. a normal/bell-shaped curve). Ex: Human height, skin color

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Wild Type

An individual with the normal (most common in nature) phenotype. Ex: red eyes in fruit flies

Mutant

An individual with a mutated form of an allele, not common in nature. Ex: white eyes in fruit flies

Linked genes

Genes located adjacent on the same chromosome that tend to be inherited together in genetic crosses.

X inactivation

one of two X chromosomes in a female is randomly inactivated and remains coiled as a Barr body

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate.

Aneuploid

Abnormal number of chromosomes.

Monosomatic

Only has one copy of a chromosome

Polyploid

condition in which an organism has extra SETS of chromosomes

Deletion

removes a chromosomal segment

Duplication

repeats a segment

Inversion

reverses a segment

Translocation

moves a segment from one chromosome to another

Down Syndrome

(Trisomy 21) Occurs when an individual has 3 chromosomes of the 21st pair instead of 2; caused by NONDISJUNCTION

Turner Syndrome

A chromosomal disorder in females in which either an X chromosome is missing ( making the person XO instead of XX) or part of one X chromosome is deleted.

Extranuclear Genes

genes found in organelles in the cytoplasm; inherited maternally (mitochondria in the egg)

DNA methylation

The addition of methyl groups to bases of DNA after DNA synthesis; may serve as a long-term control of gene expression.

locus

Location of a gene on a chromosome

Define true breeding

Breeding where organisms have 2 copies of the same allele (homozygous).

Define P generation

parental generation

Define F1 generation

The generation of offspring that results from the cross pollination of the P generation

define f2 generation

The generation of offspring that results from the self pollination of the F1 generation

what is mendel's law of segregation?

states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.
-when any individual produces gametes, the two copies separate, so each gamete receives only copy

difference between dominant and recessive

dominant will be shown, recessive will show only if homozygous recessive

difference between homozygous and heterozygous

Homozygous = 2 identical alleles
Heterozygous = 2 different alleles

difference between genotype and phenotype

genotype is the set of alleles for a gene an organism has.
Phenotype is the physical appearance of the trait; or the trait expressed.

Explain how a test cross can be used to determine if an individual with the dominant phenotype is homozygous or heterozygous.

A testcross is the breeding of an organism of an unknown genotype with a recessive homozygote (white flower). If all of the offspring are purple, the unknown genotype is PP. If some of the offspring are white, the unknown genotype must be Pp.

define mendel's law of independent assortment

The inheritance of one character has no effect on the inheritance of another character.
-one trait is not automatically inherited with another trait
-alleles for separate trait can be packaged in every possible combination into gametes
-alleles of different genes assort independently of one another during gamete formation

example of incomplete dominance and explain why it is not evidence for the blending theory of inheritance

Incomplete dominance can happen in flowers such as snap dragons where a red flower plant and a white flower plant have an offspring that is neither red nor white but is a mix so in this case it would be pink. It does not support the blending theory as it does not get its colour from the dominant plant in this case but from both.

Explain how the phenotypic expression of the heterozygote differs with complete dominance, incomplete dominance, and codominance.

-Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical.
- In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties•
-In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways.

Explain why dominant alleles do not necessarily mean that the allele is more common in the population. Illustrate your explanation with the character polydactyly.

describe the inheritance of ABO blood system and explain why the I^A and I^B alleles are said to be co-dominant

An example is the ABO blood group in humans. The gene I encodes an enzyme involved in the attachment of sugars to a glycoprotein present on the surfaces of red blood cells. There are three alleles of the gene: IA, IB, and IO. The IA and IB alleles both encode active enzymes, but the enzymes attach different sugars to the glycoprotein. The IO allele does not encode an active enzyme, so no sugar is attached at that position on the glycoprotein. When two different alleles (e.g., IA and IB) are present, both alleles are expressed (both enzymes are made, so both types of glycoproteins are made). The A and B glycoproteins are antigenic: if a red blood cell with the A glycoprotein on its surface gets into the bloodstream of a person who lacks the IA allele, the recipient produces antibodies against the "nonself" cells (FIGURE 8.11). While the A and B glycoproteins are antigenic in people who do not have the IA or IB alleles, respectively, the O glycoprotein does not provoke antibody production. This makes people who are IOIO good blood donors.

define and give an example of epistasis

definition: Interaction between genes in which the presence of a particular allele of one gene determines how another gene will be expressed. OR
-occurs when the phenotypic expression of one gene is affected by another gene. For example, two genes (B and E) determine coat color in Labrador retrievers:
An EE or Ee dog with BB or Bb is black; one with bb is brown. A dog with ee is yellow regardless of whether B or b alleles are present. Clearly, gene E determines the phenotypic expression of gene B, and is therefore epistatic to B

Describe a simple model for polygenic inheritance and explain why most polygenic characters are described in quantitative terms

Polygenic inheritance refers to an additive effect of two or more genes on a single phenotypic character. An example is skin pigmentation in humans which is controlled by at least 3 separate inherited genes.

It is usually described in quantitative terms because it is not based on an 'either-or' scenario but multiple genes and characters vary in the populations.

Many genes determine height, weight, and melanization
Simplified example of melanization
Three genes with two incompletely dominant alleles of each.
Trihybrid cross gives six phenotypes in a normal distribution

Three genes with two incompletely dominant alleles of each.

Trihybrid cross gives six phenotypes in a normal distribution

describe how environmental conditions can influence the phenotypic expression of a character

Leaves of a tree can vary in size, shape, and greenness depending on exposure to the sun. For humans, nutrition influences height, exercise alters build, sun-tanning darkens skin. The environment influences phenotype in tandem with genotype.

Environment can have powerful effects on phenotype

Simple example: temperature sensitive genes

"Norm of reaction" = phenotypic range of a genotype depending on environment

Diseases with environmental and genetic components are multifactorial

Explain why lethal dominant genes are much rarer than lethal recessive genes.

A lethal dominant gene prohibits the organism from reproducing irregardless of the paired gene, so it is removed from the gene pool as soon as it appears. A lethal recessive gene, on the other hand, does not prevent reproduction unless it is paired with another lethal recessive, so it may be passed down through many generations before becoming paired and preventing reproduction.

Describe the inheritance and expression of cystic fibrosis.

Common autosomal recessive, half survive to 30Altered trans-membrane conductance regulator, a chloride channel
High extracellular chloride excess clogging mucus

Among people of European descent, 1 out of 25 (4%), are carriers of the cystic fibrosis allele. The disease expresses itself through mucus buildup in the pancreas, lungs, digestive tract and other organs due to abnormally high concentration of extracellular chloride. Untreated children die by age 5, in the US more than half live to their 20s and 30s.

common autosomal recessive, half survive to 30, altered trans-membrane conductance regulator, high extracellular chloride excess clogging mucus

Describe the inheritance and expression of sickle-cell disease.

Sickle-cell disease is the most common inherited disorder among people of African descent (1 out of 400). It is caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells. Sickle cells clump and clog small blood vessels which can lead to physical weakness, pain, organ damage, and even paralysis. No cure; often treated through regular blood transfusions and drugs.
Autosomal recessive, many successful new treatments
Point mutation in beta-hemoglobin, changes RBC shapeRBCs clog vessels and damage tissue

autosomal recessive, many successful new treatments, changes RBC shape

describe the inheritance and expression of tay-sachs

autosomal recessive, lethal within a few years , missing hexosaminidase

Explain how carrier recognition, fetal testing , and newborn screening can be used in genetic screening and counseling.

alert prospective parents, preparations and strategies defined, ultrasound, amniocenetesis, chorionic villus sampling, risk of fetal death, allows the choice of termination, allows earliest treatment possible

Given a simple family pedigree, deduce the genotypes for some of the family members.

Suggestions for analysis Consanguinity?
Suggestions for analysis Consanguinity?
rare recessive
All affected are males? sex-inked
Every affected has an affected parent? dominant
Warning: often too little data to make definite conclusions

Define and compare linked genes and sex-linked genes. Explain why the inheritance of linked genes is different from independent assortment.

Linked genes are located on the same chromosome Sex-linked are on the X or Y chromosome

Genes on the same chromosome tend to separate together, not randomly

Comparison Linked genes are located on the same chromosome
Sex-linked are on the X or Y chromosome Genes on the same chromosome tend to separate together, not randomly

Explain why linked genes do not assort independently.

Linked genes tend to be inherited together because they are located on the same chromosome.

explain how crossing over can unlink genes

In crossing over, which occurs while replicated homologous chromosomes are paired during prophase of meiosis 1, there is an exchange of one maternal and paternal chromatid, end portions of two nonsister chromatids trade places each time a crossover occurs.

what is a genetic/linkage map?

a representation of markers on a chromosome in linear order with distances between them expressed as percent of recombination