Genetics Flashcards
DNA Contains
- Basic genetic information
- Its expressions as proteins determines the various functions of that cell
DNA Structure
Base (A, T, G, C) + sugar + phosphate
Chromosomes
23 pairs
22 autosomes, 1 sex chromosomes
Chromatin
DNA + protein (histones)
DNA Replication
- S phase of cell cycle
- Maintains genomic information using DNA polomerase
- Semi-conservative replication
- DNA repair of damaged due to replication errors or exposures
Mutation
Alteration in the DNA sequence
- May involve the insertion or deletion of nucleotides
- Can result in an aberrant protein sequence
- Improper protein structure can affect function
Redundancy
(in the genetic code) not all mutations cause amino acid changes
Silent Mutations
Mutations that do not change the amino acid
Missense Mutations
Mutations that alter the amino acid and may or may not alter protein structure and thus function
Nonsense Mutations
Mutations that may introduce a stop to protein synthesis
Human Genome Project
- Identify mutations associated with disease
- Identify markers of disease or predictors of disease risk or likelihood of response to certain drug treatments
Somatic Cells
- Are cells other than the gametes (sperm & ova)
- Contain 23 pairs of chromosomes located within the nucleus of the cell
- Are DIPLOID - having 2 copies of each chromosome
Gamate Cells
- Sperm & ova
- Are haploid - have only one copy of each chromosome
Diploid Nature
- Of somatic cells is maintained by Mitosis
Haploid Nature
-Of gamete cells is maintained by Meiosis
Male sex chromosome
XY
Female sex chromosome
XX
Homologues Chromosomes
The members of each pair of autosomes
- their sequences are very similar
- Have different alleles or copies of each of the genes
Recombination
Genetic exchange of maternal and paternal information during meiosis
Mitosis
The division of the nuclear material of a cell
-goes from 1 diploid cell to 2 diploid cells
Prophase
Phase of mitosis
-The nuclear membrane dissolves and two copies of chromosome (sister chromatides) attach to at the centeromere
Metaphase
Phase of mitosis
-The chromosmes are highly condensed and line up on the equatorial plane of the cell
Anaphase
Phase of mitosis
- The sister chromotids separate, and the chromosomes are pulled apart
Telophase
Phase of mitosis
-Where the nuclear membrane forms around the two sets of chromosomes
Cytokinesis
Follows mitosis, forming two daughter or progeny cells
Meiosis
Reduction divisions that take the chromosomal content of germline cells from diploid (23 pairs of chromosomes) to haploid (23 individual chromosomes)
-The process that produces the gamates - sperm and ovum that will fuse during fertilization to form the zygote
Before meiosis and mitosis
the DNA is copied to form sister chromatids
Meiosis I
the reduction division stage that results in the formation of 2 haploid cells per diploid cell
- Homologous chromosomes line up in the middle of the cell —- separate to opposite sides of the cell
- Random shuffling of maternal & paternal chromosomes occurs
- Crossing over between homologous segments of the sister chromotids that make up each homologous chromosome occurs = genetic recombination = genetic information to offspring is unique
- Result is 2 cells that contain 23 individual chromosomes, each has two copies or is composed of sister chromotids
Meiosis II
- Further separation of the sister chromotids generated in meiosis I to generate 4 cells each with one copy of the 23 homologous chromosomes
- From the original diploid parent cell there are now 4 haploid cells that contain 1 copy of each chromosome
Genotype
Genetic makeup
Phenotype
observable properties (traits) due to interaction between genotype and environment
Germline Mutation
A genetic change found in the gametes
-Can be transmitted to offspring or inherited
Somatic Mutation
A genetic change in one of the cells of the body and cannot be transferred to the offspring or inherited
Mendel’s First Law
The principle of segregation
- States that the two members of a gene pair (alleles) segregate (separate) from each other in the formation of gametes
- Half of the gametes carry one allele, and the other half carry the other allele
Mendel’s Second Law
The principle of independent assortment
-States that genes for different traits assort independently of one another in gamete production
Polyploidy
Complete sets of extra chromosomes
Aneuploid
Chromosome number not 23 - Trisomy - nondisjunction is common cause (failure of that chromosome to split)
-Trisomy 21 = downs syndrome
Alterations of chromosomal structure
- Inversions
- Deletions
- Translocations
- The truncated chromosome 22 - Philadelphia chromosome - associated with chronic myeloid leukemia
Complex Genetic Disorders
Complex, multifactorial or polygenic
-Indicates possibly multiple mutations or genetic changes associated with a specific disease or that there is a combination between genetic and environmental factors, or both
P
The generation that refers to the parental generation
F1
For filius or son refers to the first generation, the first filial generation of the progeny of those parentals
F2
Offspring of the F1 generation
Homozygous trait
If both copies of the gene are the same at a specific allele
Heterozygous trait
If there are two different alleles for that genetic locus
- Parents are both heterozygous for a trait = Aa, Aa
1: 4 (25%) chance that the offspring will have the disease - and will be homozygous recessive (aa) - 2:4 (50%) chance the offspring will be a carrier
- 1:4 (25%) chance the child will be free of disease (wild)
Single Trait Genetic Cross
If 2 parents are heterozygous for a trait (eg cystic fibrosis), the likelihood that any one of their children will have CF is:
- – If a trait is dominant - 3/4 chance the child will exhibit trait
- – If the trait is recessive - 1/4 chance the child will exhibit the trait
- – 3/4 chance the child will be a carrier
Single Gene disorders
- Caused by mutations in individual genes
- May be present on one or both alleles
Chromosomal disorders
-Caused by an excess or deficiency of genes contained within a whole chromosome or chromosome segment
Multifactorial inheritance disorders
- Caused by a combination of variables in a number of genes that together produce or predispose an individual to a serious defect
- Often related to environmental factors
Autosomal recessive traits
Single-locus genetic disorder
- Cystic Fibrosis
- Sickle cell anemia
Autosomal dominant traits
Single-locus genetic disorder
- Achondroplasia (dwarfism)
- Marfan syndrome (connective tissue defects)
X-linked recessive (sex linked)
Single-locus genetic disorder
- Duchenne muscular dystrophy
- Hemophilia A
Mitochondrial
Single-locus genetic disorder
- Affects energy metabolism
- Presents with multiple copies
- Is inherited from the mother only
Nondisjunction
Occurs during meiosis when there is failure to separate chromosomes (meiosis I) or sister chromatids (meiosis II)
Turner Syndrome
Chromosomal disorder involving sex chromosomes
-absence of all or part of the X chromosome
Klineferlter Syndrome
Chromosomal disorder involving sex chromosomes
- One or more additional X chromosomes with a normal male composition (XY)
