Chapter 7: Heredity Flashcards
Gregor Mendel
Studied inheritance using garden peas.
Particulate Inheritance
Inheriting characteristics through genes.
Multiplication Rule
The rule of probability used when there are two independent events.
Addition Rule
The rule of probability used when there are related events.
Law of Dominance
If you cross a homozygous dominant organism with a homozygous recessive organism, you will get a hybrid, but it will have the dominant phenotype.
Law of Segregation
During the formation of gametes, the traits of the parents separate.
Monohybrid Cross
Cross between two hybrids.
Testcross
A cross used to determine the genotype of an organism, because an organism that has a dominant phenotype is either TT or Tt.
Law of Independent Assortment (Dihybrid Cross)
When a cross is carried out between tow individuals hybrid for two or more traits on different chromosome.
If genes are linked (if the gene for yellow seed color was linked to gene for tall), they will not assort independently.
Incomplete Dominance
Also known as blending. For example, a red (RR) Japanese 4 o’clock flower crossed with a white (WW) 4 o’clock flower will create pink (RW) offspring.
Codominance
Where both traits are present. A good example is the MN blood group, where its surface molecules are those of MM and NN.
Multiple Alleles
When there are more than two allelic forms of the same gene, such as the four blood types: A, B, AB, and O.
Pleiotropy
The ability of a gene to have multiple affects on the organism. An example is cystic fibrosis, where the thickening of mucus on cells causes poor absorption of nutrients and chronic bronchitis.
Epistasis
When a trait is controlled by two genes, but one gene masks the other one. For example, in agouti mice, the mouse can only come in three colors: agouti, black, and white. However, the gene for B is epistatic to A, so when B is gone, the mouse will be white.
Polygenic
Where the phenotype of the genes can vary along a spectrum. For example, skin color and tallness are examples, because the tallness and color skin varies between all people.
Multifactorial Disease
When an underlying genetic component has a substantial environmental influence. For example, risk for heart disease can increase with bad genetics, but also can be caused through unhealthy foods and meat.
Penetrance
The percentage of organisms with a genotype that actually exhibits the expected phenotype.
For example, many people with the genotype for breast cancer do exhibit it sometime in their life, but some never develop breast cancer.
Linked Genes
Genes on the same chromosome.
Sex-Linked Traits
Traits carried on the X chromosome (Few are carried on the Y chromosome).
Recessive Sex-Linked Traits
A female will express the phenotype only if she carries two mutated genes. Examples include color blindness, hemophilia, and Duchenne muscular dystrophy.
Dominant Sex-Linked Traits
A female will express the phenotype if she inherits only one mutated gene. Males inherit only one X linked gene, so if he inherits a mutated one, he will express it.
Chiasma
A physical bridge made at the place where crossing over occurs.
Recombination
The result of a cross-over.
Recombination Frequency
The likelihood that the cross-over will occur.
Barr Body
The dark spot of condensed chromosome that an inactive X becomes.
Mutations
Changes in the genome that can occur in gametes or somatic cells, and often by random chance.
PKU
Autosomal recessive disease that causes an inability to break down phenylalanine.
Cystic Fibrosis
Autosomal recessive. Characterized by buildup of extracellular flu in the lungs, digestive tract, etc.
Tay-Sachs Disease
Autosomal recessive. Caused by the lack of enzyme to break down lipids for brain function.
Huntington’s Disease
Autosomal dominant. A degenerative disease of the nervous system.
Hemophilia
Sex-linked recessive. Caused by the absence of normal proteins used for blood clotting.
Color blindness
Sex-linked recessive.
Duchenne muscular dystrophe
Sex-linked recessive. Progressive weakening of the muscles and loss of control.
Sickle-cell disease
Autosomal recessive. Mutation that results in deformed blood cells, but carriers are resistant to malaria.
Down Syndrome
47 chromosomes due to trisomy 21. Mental retardation, characteristic facial features, prone to leukemia.
Karyotype
Procedure that shows the size, number, and shape of chromosomes to alert abnormalities.
Chromosomal Mutation Types
- Deletion: a fragment of the chromosome is lost during cell division.
- Inversion: when a chromosomal fragment detaches and reattaches in the opposite orientation.
- Translocation: when a fragment of a chromosome reattaches to a wrong chromosome.
- Polyploidy: when a cell or organism has an extra set of chromosomes.
Nondisjunction
When chromosomes fail to separate as they should, often in meiosis.
Aneuploidy
Any abnormal number of chromosomes.
Trisomy
When a chromosome is present in a triplicate.
Triploid
An organism that has an extra set of chromosomes.
Genomic imprinting
A variation in phenotype depending on whether the trait is inherited from the mother or the father. Occurs during gamete formation.
Extranuclear Genes
Genes located in the mitochondria or chloroplasts. Linked to several very rare and severe inherited diseases in humans.
