genetic Flashcards
Structure of Deoxyribonucleic Acid (DNA)
-made up of nucleotides
-sugar, phosphate group, one of 4 bases ACGT
-arranged in double helix with hydrogen bonds in the middle
Chromosomes
threadlike DNA composed of
chromatin only visible during cell division
-humans have 23 pairs of chromosome
-entire set of human chromosomes is the human genome
-we also have non coding DNA called pseudo genes - genetic information that is not used or is edited out of mRNA before proteins are made.
Gene
-on a chromosome a short sequence of DNA that will be transcribed to premRNA then protein
-always found a fixed location (locus)
-introns are non coding portions that interpret sequences
-during RNA splicing introns -intervening sequences are removed and exons EXpressed
Alleles
-different versions of a gene found at the same loci causing different phenotype
-everyone has 2 copies of each gene so you can have 2 different or 2 same alleles
-homologous chromosomes are matching pair of chromosomes
-loci are alleles can be hetero or homo
Dominant gene
A gene whose effects are seen and is capable of masking the effects of
a recessive gene for the same trait (often represented by uppercase letters)
Codominance:
Both dominant genes are expressed. 2 or more genes that are dominant and when they appear together produce a combined effect in offspring e.g. blood type Group AB has both the A and the B antigens
Genetic carrier:
A person who carries a recessive gene but does not show its effects because it is masked by dominant gene
Hereditary Traits
Dominant genes/alleles
Recessive genes/alleles
Co-dominant genes:
Dominant genes/alleles: phenotype is always present
Recessive genes/alleles: phenotype is always masked by the Dominant allele and will only be expressed in the
HOMOZYGOUS state
Co-dominant genes: both alleles will express the phenotype
Traits can be physical attributes or hereditary diseases
How do we inherit genes
Inheritance is known as:
* Autosomal if the gene is found on chromosomes 1-22
* Sex-Linked if the gene is found on the X or Y chromosome
1 chromosome from each parent = 1 gene from each parent through meiosis dividing chromosomes into haploid gametes
➢Two potential alleles
Genetic Variation
what are autosomes
Normal variation among offspring is increased by:
autosomes-Twenty-two pairs of chromosomes. they are almost identical
the leftovers are called sex chromosomes and dont match
Normal variation among offspring is increased by:
Independent assortment of chromosomes during gamete formation
➢Crossing-over of genes between partners during meiosis.
-Meiosis produces gametes with 23 chromosomes each. When two gametes join they form a zygote with 46 chromosomes
Crossing-Over
-form of recomb
-genes from one location “cross over” to the same location on the matching gene and as the chromosome separates and gets back together each will pick up new genetic material from the other
Nondisjunction:
failure of a chromosome pair to separate
during gamete production, causing trisomy or monosomy in the offspring.
Aneuploidy -Numerical Abnormalities
-abnormal number of chromosomes.
-non modal chromosome amount either 1 extra -47 or 1 less -45. Happens in both autosomes and sex chromosomes
Down Syndrome: Trisomy 21
Chromosomal Disease
-extra copy of chromosome 21
-mental impairment
-structural defects- short hands/feet, heart disease, large tongue
Klinefelter Syndrome
Chromosomal Disease
-long legs, low intelligence, sterility , pulmonary disease
-two or more X with a Y so a man with womanly features
Turner Syndrome XO syndrome:
Chromosomal Disease
-nondisjunction of sex chromosome during gamete formation
-monosomy of sex chromosomes - XO genotype- affects women only one x chromosome is missing
- failure of sex organs to mature causing sterility, short stature, learning disorders but only in certain area like math but not reading
Gene Mutation checkpoints
what happens if a cell is too damaged
cell either continues or undergoes apoptosis
G1- before S phase. Check to make sure cell is proper size and has correct proteins for synthesis. Cell growth checkpoint. Where spontaneous mutations are repaired
G2- DNA synthesis checkpoint which occurs during 2 phase before mitosis. checks to see if DNA has been replicated properly
cytokinesis is the physical process of division
if a cell is too damaged it will go through
senescence - dormancy
apoptosis
unregulated division causing a tumor
what is a mutagen
-causes mutations that changes DNA structure , bases or alter pairings, they can distort the helix
Can be chemical
Alkylating agents (e.g. mustard gas)
➢Intercalating agents (e.g. ethidium bromide used in Molecular
➢Radiation: X-rays, UV light
➢Viruses
Mutations in cells
somatic
germ line
SOMATIC mutations occur in non-gamete
cells that cause a mutated protein which can be passed through mitosis and cause disease like cancer
germ-line - spontaneous but it will get passed through meiosis and become hereditary
mutation can be beneficial, harmful or have no harm like albinism or color blindness
Colour-blindness
-recessive x linked so a female carrier can have sons with color blindness
Red-green color blindness is sex linked but blue blindness affects both men and women as it is non sex linked
➢Epigenetics
imprinting
science describing how offspring can have mutations that not passed down but environmental. for example diet or lifestyle that can turn the gene off or on. So like twins that are genetically predisposed to lung cancer but only the one that smokes gets it
Mitochondrial Inheritance
-Inheritance of mDNA from mother ONLY
-mitochondria from sperm do not survive after ovum fertilization
-mDNA has genetic code only for enzymes in metabolic pathway that recharges ATP but this also increases potential for carrying mutations that cause disease
Acquired versus Inherited
acquired - mutation in specific cells at some time in a persons life- skin cancer
inherited - occur during reproduction present throughout the persons life in every cell - Trisomy 21
Cystic fibrosis:
Single-Gene Disease
recessive autosomal
-excessive sweating and mucus production affecting digestive and respiratory tracts
