Heredity Flashcards
Gregor Mendel
“Father of Modern Genetics”: monk who bred garden peas to study the patterns of inheritance
Mendel’s Approach to Inheritence
First, he studied traits that were clear-cut with no intermediates between varieties. second, he collected data from a large sample, with plants from several generations. Third, he applied statistical analysis.
Blended Inheritance
19th century belief that traits were passed in a mixture of fluids from parents to children and blended together
Particulate Inheritance
Mendel’s Theory: inherited characteristics are carried by discrete units, genes (he called them elements)
Probability: Multiplication Rule
To find the probability of two independent events happening, multiply the chance of one happening by the chance that the other will happen.
Probability: Addition Rule
When more that one arrangements of events producing the specific outcome is possible, the probabilities for each outcome are added together.
Law of Dominance
Mendel’s First Law: states that when two homozygous for two opposing traits are crosse, the offspring will by hybrid but will exhibit only the dominant trait and the trait that remains hidden is recessive
Law of Segregation
During the formation of gametes, the two traits carried by each parent separate.
Monohybrid Cross
(Tt)(Tt); the phenotype ratio from this cross is 3:1 (dominant to recessive); the genotype ratio is 1:2:1 (25% homozygous dominant: 50% heterozygous: 25% homozygous recessive)
Testcross: (B/b)(b/b)
Phenotype is 1:1 and genotype is also 1:1. Half will by heterozygous for this trait and half will be homozygous recessive.
Testcross: (B/B)(b/b)
Phenotype is 1 and genotype is also 1. All the offspring will be heterozygous for this trait.
Law of Independent Assortment
Applies when a cross is carried between two individuals for two or more traits that are not on the same chromosome.: Staes that during gamete formation the alleles of a gene for one trait segregate independently from the alleles for another trait. (REMEMBER: Meiosis I line up is random)
Dihybrid Cross
A cross between two F(1) plant because it is a cross between two individuals that are hybrid for two different traits.
Dihybrid Cross: Phenotype Ratio
9:3:3:1
Incomplete Dominance
Characterized by blending. Ex. a black animal mates with a white animal and produces grey babies.
Codominance
Both traits show. Ex. MN blood groups in humans, if you get M and N it’s not heterozygous both M and N are expressed.
Multiple Alelles & Blood Types
When there are more that two allelic forms of a gene. Ex. in humans there are 4 blood types determined by three alleles A, B and O. A and B are codominant and O is recessive.
Blood Type A
can be homozygous (AA) or hybrid (Ai)
Blood Type B
can be homozygous (BB) or hybrid (Bi)
Blood Type AB
codominance (AB)
Blood Type O
expressed as: ii
Pleiotropy
The ability of one single gene to affect and organisms in several ways.
Pleiotropy: Frizzle Trait
In chickens, the frizzle trait is a gene for a malformed feather. This mutation causes the development of feathers that cannot keep the animal warm and results in changes to several organ systems.
Pleiotropy: Siamese Cats
The same allele responsible for the body’s coloration is the same one responsible for the crossed eyes.
Marfan Syndrome
Pleiotropy in humans in which a single defective gene results on abnormalities of the eyes, skeleton, and the great blood vessels.
Epistasis
Two separate genes control one traits by one gene masks the expression of the other gene. The gene that masks the expression of the other gene is epistatic to the gene it masks.
Epistasis: Guinea Pigs
The gene for the production if epistatic to one for the deposition of melanin. The gene related to production has two alleles, C, which causes the pigment to be formed and, c, which does not. c/c results in no melanin produced. The second gene has an allele which causes, B, deposition of melanin and an allele, b, which causes deposition of a moderate amount of melanin. Neither B nor b can deposit melanin if C is not present.
Polygenic Inheritance
Characteristics that result from a blending of several separate genes that vary along a continuum. Ex. skin color, hair color and height. This always results in a bell-shaped curve of traits.
Nature v. Nurture
How much does the environment alter the expression of genes. Does genetic predisposition overpower the power of the environment or not?
Sex-Influenced Traits
Inheritance can be influenced by the sex of the individual. Males are more influenced by this than women because women can be carries for X-Linked traits. Ex. male pattern baldness
Linked Genes
Genes on the same chromosome that do not assort independently unless separated by a crossover event.
Sex-Linkage
Refers to X-Linked traits. Women can be carriers for Sex-Linked Recessive Traits while men cannot. Sex-Linked Dominant traits will show if the male or female has the affected X.
Autosomes
44 chromosomes
Common Sex-Linked Recessive
color blindness, hemophilia, Duchenne muscular dystrophy
Sex-Linked Recessive: Daughters
All daughter of affected fathers are carries. In order for a female to have a sex-linked recessive disorder she must inherit the gene from both parents.
Sex-Linked Recessive: Sons
Sons cannot inherit a sex-linked trait from the father because the son inherits the Y chromosome from the father. A son has a 50% change of inheriting a sex-linked trait from a carried mother.
Chiasma
The site where a crossover and recombination occur.
What type of genes are most likely to be separated during a crossover event?
Two genes that are far apart on the same chromosome.
Map Unit & Linkage Maps
Distance within which recombination occurs 1 percent of the time. It does not give information about the actual distance but it tells us the order which creates a Linkage Map.
Pedigree
Family tree that indicated the phenotype of one trait being studied for every member of a family. Geneticists use it to determine how a trait is inherited.
Genetic Mosaic
Easy in the development of the embryo of a female mammal, one X chromosome is inactivated in each somatic cell. This results in a genetic mosaic where some cells have one X inactivated and others have the other inactivated.
Barr Body
Dark spot of chromatin (the inactivated chromosome) on the outer edge nucleus on all the somatic cells in the female.
Mutations
Any changes in the genome. Can be responsible for caner or can occur during gametogenesis and affect future offspring.
Gene Mutation
Changes in the DNA sequence.
Chromosome Mutation
Show in karyotypes; changes in the normal distribution/shape of a chromosome.
Phenylkenturia
Autosomal Recessive: inability to break down the amino acid phenylalanine which requires elimination of it from the diet or mental retardation will occur
Cystic Fibrosis
Autosomal Recessive: 1/25 caucasians in a carrier and it is the most common lethal genetic disorder which is characterized by build up of extracellular fluid in the lungs, digestive tract, etc.
Tay-Sachs Disease
Autosomal Recessive: Caused by lack of an enzyme needed to break down lipids needed in normal brain function which results in seizures, blindness and early death and it’s common in Ashenazi Jews
Huntington’s Disease
Autosomal Dominant: degenerative disease of the nervous system resulting in early death and onset near middle age
Hemophilia
Sex-Linked Recessive: caused by the absence of one or more proteins necessary for normal blood clotting
Color Blindness
Sex-Linked Recessive: red-green colorblindness in rarely more than an inconvenience
Duchenne Muscular Dystrophy
Sex-Linked Recessive: progressive weakening of muscle control and lack of coordination
Sickle Cell Disease
Autosomal Recessive: point mutation in the gene for hemoglobin results in deformed red blood cells when oxygen tension is low which can cause tissues to be deprived of oxygen and carriers are resistant to malaria
Down Syndrome
47 chromosomes due to trisomy 21; mental retardation, characteristic facial features, prone to Leukemia and Alzheimers
Turner’s Syndrome
(XO) 45 chromosome due to missing sex chromosome; small stature, female
Klinefelter’s Syndrome
(XXY) 47 chromosomes due to an extra X chromosome; have male genitals but the testes are small and men are sterile
Chromsome Deletion
when a fragment lacking a centromere is lost during cell division
Chromosome Inversion
when a chromosomal fragment reattaches to its original chromosome but in reverse orientation
Chromosome Translocation
when a fragment of a chromosome becomes attached to a non-homologous chromosome
Polyploidy
when a cell or organism has extra sets of chromosomes
Nondisjunction
error that occurs during meiosis in which homologous chromosomes fail to separate as they should; one gamete receive two of the same chromosome and another receives no copy
Aneuploidy
abnormal amount of chromosomes; cancer cells almost always have extra chromosomes
Trisomy
chromosome present in triplicate
Polyploid
an organisms with extra sets of chromosomes
Extranuclear Genes
genes found in the mitochondria and chloroplasts; mitochondrial genes are inherited from the mother
Extranuclear Gene Abnormalities
Very severe because changes in mitochondrial DNA can reduce the amount of ATP a cell can make and cells such as nervous or muscle cells are especially vulnerable to this.
