Bio semester fall review non paper

Turner's syndrome

Caused by nondisjunction of the X chromosomes; X instead of XX

From Molecule to Phenotype

Changes in the DNA sequence of a gene can change proteins:
- Altering amino acid sequences
- Affecting the phenotype

Karyotype

the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size

Sex Chromosomes

Two of the chromosomes in the human genome are sex chromosomes.
- Females: XX
- Males: XY
- More than 1400 genes are found on the human X chromosome
- The human Y chromosome contains only ~158 genes

Autosomal chromosomes

all the other genes in the body that are not sex-linked.

Transmission of Human Traits

Many human traits follow a pattern of simple dominance.
Ex: the gene MC1R helps determine skin & hair color
- The alleles allow for many human genes to display codominant inheritance

simple inheritance

Phenotype determined by interactions between a single pair of allele

Sex-linkage in Human Genetics

- The X and Y chromosomes determine sex
- The genes located on them show sex linkage
- Colorblindness is a sex-linked trait

X chromosome inactivation

Most genes in one of the X chromosomes are switched off, forming a region known as a Barr body.
- Female calico cats are tri-colored
- The color of spots on their fur is controlled by a gene on the X chromosome

Pedigree

A chart that shows how a trait and the genes that control it are inherited within a family. Shaded = presence of condition, square = male, circle = female

Nondisjunction

When homologous chromosomes don't separate as they should; gametes with an abnormal number of chromosomes may result. In meiosis I, all gametes are abnormal; in meiosis II, half of the gametes produced are abnormal--the other half are normal

Trisomy

3 copies of a chromosome

Monosomy

missing a chromosome

Down Syndrome (Trisomy 21)

The most common form of trisomy that involves 3 copies of chromosome 21

Klinefelter's syndrome

a chromosomal trisomy caused by nondisjunction, where males have an extra X chromosome, resulting in XXY instead of XY

cystic fibrosis (CF)

- In most cases, it's the result of the deletion of 3 bases in the DNA of a single gene
- The body doesn't produce CFTR
- Causes thick mucus to build up in the organs, leading to breathing problems

Genetic Advantages

Some alleles that cause disease may also have benefits.
- Carrying one copy of the sickle cell provides protection from malaria
- Carrying one copy of the CF (cystic fibrosis) allele provides protection from typhoid bacterium

Genome

All the genetic information in an organism; all of an organism's chromosomes.

Trait

specific characteristic (e.g., seed color, plant height) of an individual

Hybrid

created from cross of true-breeding individuals

Cross-pollination

pollination of a flower or plant with pollen from another flower or plant.

Genes

passed from one generation to the next; determines an individual's characteristics

Alleles

the different forms of a gene. Characteristics such as seed color are determined by genes

Dominant allele

An allele whose trait always shows up in the organism when the allele is present. Represented using a capital letter

Recessive allele

An allele that is hidden whenever the dominant allele is present. Represented using a lowercase letter

segregation

Separation of alleles during gamete formation; Mendel's first law

Homozygous

has two identical alleles for a gene

Heterozygous

has two different alleles for a gene

Genotype

genetic makeup

Phenotype

physical traits of an organism. Two organisms may share the same phenotype but have different genotypes (ex., GG & Gg)

Independent assortment

Genes for different traits can segregate independently during the formation of gametes; Mendel's second law

1st generation (F1) Punnett Square

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

2nd generation (F2) Punnett Square

A chart that shows all the possible combinations of alleles that can result from cross pollination/self pollination the bigger one

Genotype ratio

the ratio of the genotypes that appear in offspring; homozygous dominant : heterozygous : homozygous recessive (ex., 1:2:1)

F1 Phenotype ratio

the ratio of phenotypes produced by a cross; dominant : recessive (ex., 3:1)

F2 Phenotype ratio

Dominant for both traits : Dominant for the first trait & recessive for the second : Recessive for the first trait & dominant for the second : Recessive for both traits (ex., 9:3:3:1)

Incomplete dominance

One allele is not completely dominant over another

Codominance

The phenotypes for both alleles are clearly expressed

Multiple alleles

Genes that exist in more than two forms (ex., human blood types, fur color in rabbits)

Genotypes of blood types

A: IAIA or IAi

B: IBIB or IBi

AB: IAIB

O: ii

Polygenic traits

- Many traits are produced by the interaction of several genes

- Examples: eye color in fruit flies, coat color in dogs

- Traits typically show a wide variety of phenotypes

Gender genotypes

XX - female

XY - male

Homologous

chromosomes with the same genes, are originally from each of the organisms parents

Mitosis

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

Diploid

containing both sets of homologous chromosomes; 2N

Haploid

containing only a single set of chromosomes; (1)N

Gamete

a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote; sex cell

Somatic Cells

any cell of a living organism other than the reproductive cells.

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

Crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis.

Prophase I

The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.

Metaphase I

The pairs of homologous chromosomes line up in the center of the cell. The centromere of each chromatid pair attaches to one spindle fibre.

Anaphase I

Homologous chromosomes are pulled to opposite ends of the cell. Note that chromatids do not separate - each duplicated chromosome still has two chromatids.

Telophase I and Cytokinesis

Two haploid cells form; each chromosome still consists of two sister chromatids

Prophase II

The duplicated chromosomes and spindle fibers reappear in each new cell.

Metaphase II and Anaphase II

Chromosomes line up in the center of the cell and sister chromatids are pulled apart.

Telophase II and Cytokinesis

A nuclear envelope forms around each set of chromosomes. the cytoplasm divides. The end product is four daughter cells that have half the normal chromosome number

Gene Linkage

Alleles of different genes tend to be inherited together when those genes are located on the same chromosome

Chromosome

A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins

Chromatid

one of two identical "sister" parts of a duplicated chromosome

Centromere

Area where the chromatids of a chromosome are attached

Tetrads

the paired chromosomes consisting of four chromatids

RNA

- ribose sugar
- generally single-stranded
- contains uracil (U) instead of thymine (T)

RNA types

mRNA, tRNA, rRNA

Messenger RNA (mRNA)

A type of RNA, synthesized from DNA and attached to ribosomes in the cytoplasm; it specifies the primary structure of a protein.

Ribosomal RNA (rRNA)

A type of RNA that helps build the ribosome, which is made up of 2 subunits. These subunits consist of several molecules of rRNA and many proteins (up to 80!).

Transfer RNA (tRNA)

During protein synthesis, tRNA molecules carry amino acids from the cytoplasm to the rRNA

Transcription

Segments of DNA serve as templates to produce complementary mRNA molecules. First step of RNA synthesis

RNA polymerase

An enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription. It can proofread, though only to an extent.

Promoters

RNA Polymerase (enzyme) binds only to promoters ("regions") of DNA that have specific base sequences.

Codon

A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

Start Codon

A codon that signals to ribosomes to begin translation; codes for the first amino acid in a protein. AUG (methionine) is the start codon

Stop codon

UAG, UAA, or UGA; the codon that ends all RNA.

Amino Acid

Building blocks of protein

Translation

The process by which mRNA is decoded and proteins are produced. Starts when a ribosome attaches to an mRNA molecule. Then, tRNA molecules, carrying amino acids with them, bind to (mRNA) codons. The ribosome helps form a peptide bond. It breaks the bond holding the first tRNA molecule to its amino acid. The ribosome reaches a stop codon, releasing the newly synthesized polypeptide and the mRNA molecule, completing the translation process.

Gene Expression in Prokaryotes

-no nucleus
-transcription and translation are coupled
-DNA binds proteins that regulate genes by controlling transcription
-One of the keys to gene transcription in bacteria is the organization of genes into operons

Operon

a group of genes that operate together

Lac operon

When lactose is not present, the lac genes are turned off by regulating proteins that bind to DNA and block transcription

operator

Region of DNA that controls RNA polymerase's access to a set of genes with related functions.

lac repressor

a protein that binds to the operator site of the lac operon and inhibits transcription

Gene Expression in Eukaryotes

-transcription in nucleus
-translation in cytoplasm
-mRNA processing precedes translation
-has a TATA box

TATA box

crucial promoter DNA sequence in eukaryotic genes

Transcription Factors

control the expression of these genes by binding to certain DNA sequences (ex., DNA polymerase)

Homeotic Genes

-regulate organ development
-code for transcription factors
-HOX genes determine the identities of each body segment

Homeobox genes

Homeobox genes are a type of homeotic gene that encode proteins that bind to DNA; these proteins tell cells in various segments of the developing embryo what type of structures to make.

Environmental Effects

-Environmental factors (ex., pollution) can affect gene regulation
-Temperature can affect the development of some animals

Epigenetics

The study of influences on gene expression that occur without a DNA change; genes that can turn on and off during certain stages of an organism's life cycle

Mutations

random heritable changes in DNA. There's gene mutations and chromosomal mutations

Gene Mutations

Mutations that produce changes in a single gene (ex., sickle cell anemia)

Point Mutation

Gene mutation involving changes in one or a few nucleotides.

Substitution

A mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide

silent mutation

Consequence of substitution where the new codon produces the same amino acid. The protein remains unchanged.

missense mutation

Consequence of substitution where the new codon produces a different amino acid. ONE amino acid is changed in the sequence.

nonsense mutation

Consequence of substitution where the new protein signals "stop" instead of producing an amino acid. The protein becomes shorter.

insertion mutation

a mutation in which one or more nucleotides are added to the code

deletion mutation

a mutation in which one or more pairs of nucleotides are removed from the code

Frameshift mutation

Consequence of insertion & deletion that causes ALL following codons to be regrouped, which changes EVERY amino acid after the point of insertion/deletion

Chromosomal Mutations

deletion, duplication, inversion, translocation; changes in the cell's chromosome section

Deletion mutation

a mutation in which one or more pairs of nucleotides are removed from a gene

duplication mutation

a mutation that involves the duplication of a region of DNA on the same strand