UNIT 11 - HUMAN GENETICS Flashcards
Hereditary
Transmission of traits from one generation to the next
Genetics
Scientific study of heredity and hereditary variation
Gene (6)
- Unit of hereditary that controls particular character
- Sequence of DNA
- Specific location on a chromosome
- Determines particular character
- Controls cellular structure/activities
- Determines chemical structure of structural proteins of cell & enzymes
Allele
Specific form of gene which controls trait (eg. Specific allele for a hair color gene determines that an individual will have trait brown hair)
Character
Observable feature such as hair color and eye color
Trait
Variant of a character such as red hair or brown hair
Phenotype
An organism’s physical appearance
Genotype
An organism’s genetic makeup
Chromatin
Complex of DNA and protein that form chromosomes
Chromatid
Duplicated strands of DNA joined at the centromere during cell division
Chromosome
Large condensed and organized structures formed by tightly coiled chromatids
Diploid cell
2 sets of chromosomes found in all body cells except gametes
Haploid cell
1 set of chromosomes found only in gametes (sperm and egg)
Somatic cell
Cells in the body other than sperm and egg cells and contain 46 chromosomes (23 pairs) where each pair is from maternal and paternal sources
Autosomes
Any non-sex chromosome; 22 pairs
Sex chromosomes
1 pair of sex chromosomes
Female sex chromosome
XX
Male sex chromosomes
XY
Homologous
Means same information
Mitosis
Process by which one cell gives rise to 2 daughter cells
Why must cells divide by mitosis (2)
- Growth: From fertilized egg to multi celled organism
- Repair & renewal: Replace cells that die from normal wear and tear or injury
Cell cycle (5)
- Interphase (non-dividing): Cell growth, DNA replication, organelle replication
- Mitotic phases (prophase, prometaphase, metaphase, anaphase, telophase): Duplicated chromosomes separate
- Cytokinesis: Division of cytoplasm
- Two daughter cells produced
- Identical to parent cell
Interphase:
Cell prepares for division
Prophase
Condensation of chromatin into visible chromosomes
Metaphase
Alignment of chromosomes at the cell’s equator
Anaphase
Separation of sister chromatids towards opposite poles
Telophase
Nuclear envelope forms and chromatin relaxes
Cytokinesis
Cytoplasm divides and two genetically identical daughter cells form
Meiosis
Reproductive cell division that occurs in gonads and produce cells (gametes) with a haploid number of chromosomes and fertilization restores the diploid number of cells
Major differences between mitosis and meiosis
Mitosis occurs in somatic cells, two daughter cells formed, number of chromosomes remains diploid in daughter cells, necessary for growth and repair, and crossing over does not take place. Meiosis occurs in gametic cells, four daughter cells formed, number of chromosomes become haploid in daughter cells, meiosis is necessary for sexual reproduction and crossing over takes place
Nondisjunction
Refers to the failure of paired chromosomes to separate normally resulting in abnormal distribution of chromosomes in daughter cells
Crossover and genetic recombination (3):
- Homologous chromosomes synapse during prophase of meiosis I. Each chromosome consists of two sister chromatids
- One chromatid segment exchanges positions with a homologous chromatid segment and crosses over (chiasma)
- Each haploid gamete has one of the four chromosomes, two of the chromosomes are recombinant (new combination of genes)
Dominant alleles
Masks the expression of another allele; do not skip generations and not hidden
Recessive alleles
Presence is masked by dominant alleles; may be present but not expressed, can skip generations, expressed when both alleles recessive, MUST have 2 recessive alleles for trait to show
Dominant and recessive alleles symbols
Dominant gene upper case, recessive gene lower case
Homozygous
Same alleles on homologous chromosomes
Homozygous dominant
RR
Homozygous recessive
rr
Heterozygous
Different alleles on homologous chromosomes (Rr)
Autosomal inheritance
Involves characteristics coded by genes on autosomes (1-22 AKA non sex chromosomes)
ABO gene
Located on chromosome 9, everyone has two copies of chromosome 9 so you have two ABO genes (from mom and dad)
Mutation (5)
- Sudden change in cell’s genetic material
- Permanent alteration
- Can be inherited
- Spontaneous/induced (chemicals, irradiations)
- Affect single gene and affect number of chromosomes at once
How would a gene mutation be expressed in offspring
The mutation would have to be dominant, or would have to be present in a cell with a recessive allele inherited from other parent
Wildtype allele
Used to describe the most common allele of any particular gene and used in situations where they may be an interest in comparing a rare mutant allele with the normal or wild type
Albinism
Characterized by lack of pigmentation (melanin) in skin, hair and eyes caused by inability of melanocytes to manufacture tyrosinase which converts tyrosine to melanin
Downsides of albinism (3)
- Visual problems
- Possible blindness due to light damage of retina
- Sensitivity to UV radiation from sunlight
Dominant disorders:
Usually lethal and much rarer than recessive disorders (eg. Polydactylism, Huntington’s disease, achondroplasia)
Huntington’s disease
Gradual degeneration of nervous tissue and mental function, symptoms appear after 40
Aneuploidy
Cell from which one or more chromosome has been added or deleted
Monosomic:
Missing a chromosome (2n-1)
Trisomic
Has an extra chromosome (2n+1)
Down syndrome:
Aneuploidy either during gametogenesis or during early embryonic development and occurs in 1 in 900 births, most prevalent in older mothers (eg. 47, XX, +21; trisomy 21)
Down syndrome features (8)
- Mental retardation
- Short head
- Short neck
- Short torso
- Heart defects
- Poor skeletal development
- Slanted eyes
- Enlarged tongue
Turners syndrome
Result of aneuploidy in sex chromosomes, missing 1 X chromosome (45, X0)
Turners syndrome features (4)
- Lack of breast development and other secondary sex characteristics
- Small in body size
- Growth retardation
- Webbing of neck
Klinefelter syndrome
Sex chromosome aneuploidy, extra X chromosome in male (47, XXY)
Klinefelter syndrome features (6)
- Poorly developed secondary sex characteristics
- Sterility (no sperm)
- Small testes
- Breast development
- Increased height, long limbs
- Decreased mental abilities
Sex linked inheritance
Gene located on either sex chromosomes, generally refers to genes on X chromosome
Colorblindness
Sex linked condition where females may be carriers and males are typically affected
