genetics Flashcards
what are genetics?
scientific study of heredity
who was mendel?
studied garden peas because they were easy to grow, came in many readily varieties, easily manipulated, can self-fertilize, and readily available, first person to analyze patterns of inheritance, and deduced fundamentals of genetics
what are the generations?
the hybrid offspring are the F1 generation, and a cross of the F1 plants form the F2 generation
what is a monohybrid cross?
a cross between pure-bred parent plants that differ in only one character/trait
what is purebred?
derived from parents who are homozygous for certain traits
what are hybrids?
offspring of two different purebred varieties, the parental plants are the P generation
what do geneticists do ?
distinguish between an organism’s physical appearance & its
genetic makeup.
what is a phenotype?
An organism’s physical appearance
what does a Punnett square predict?
-the probability of a trait happening
- the four possible combinations of gametes &
- the four possible offspring in the F2 generation
what is a genotype?
An organism’s genetic makeup
what are the rules of probability?
Rules of probability apply to the inheritance of single gene traits.
Thus if the genotypes of parents are known, it is possible to establish a child’s chances for inheriting a particular genotype & thus for having a particular trait.
what is genetic makeup?
Alleles
what is a dihybrid cross?
the mating of parental varieties differing in two characters
What would result from a dihybrid cross?
- dependent assortment or
- independent assortment.
what is Mendel’s law of segregation?
During gamete formation, the alleles of each gene segregate from each other so that each gamete carries only one allele for each gene. 3:1 (phenotypically)
what is a testcross?
a mating between
* an individual of dominant phenotype (but unknown genotype
(e.g Bb or BB?) &
* a homozygous recessive individual.
what is Mendel’s law of independent assortment?
Genes for different traits can segregate independently of the other genes during the formation of gametes.
Ex. Labradors – mating of double heterozygotes – 9:3:3:1
Mendel’s principles apply to the
inheritance of many human traits.
family pedigree-
Earlobe attachment
* Tongue rolling
* Dimples
* Handedness
* Freckles
* Curly-straight hair
* Hairline shape
* PTC tasting (phenylthiocarbamide)
* Red-green color blindness
what can prolonged geographic isolation lead to?
can lead to
inbreeding, the mating of close relatives
what are wild type traits?
Typical form as it occurs most often in nature &
Not necessarily specified by dominant alleles
what is a common mistake to family pedigrees?
dominant traits are not necessarily more common, dominant trait is expressed over the recessive trait
what is genetic homozygosity?
inheritance of same form of gene from both parents
what is Habsburg jaw?
likely the result of centuries of inbreeding among
the kings & queens of Spanish Habsburg dynasty
what does inbreeding do?
increases the chance of offspring that are homozygous
for a harmful recessive trait.
what are single genes called?
lethal alleles
how are human traits controlled?
they show simple inheritance patterns and are controlled by single genes on autosomes
are genetic disorders recessive or dominant?
recessive
what are carriers?
Individuals who have the recessive allele but appear normal
what is lethal recessive and examples of the disorders?
affected(aa), carrier(Aa), normal (AA)
PKU
* Sickle Cell Anemia
* Tay Sachs
* Cystic fibrosis
* Galactosemia
* Xeroderma pigmentosum
* Hearing/Deafness
what is lethal dominant and examples of the disorders present?
normal(aa), affected(Aa), affected(AA)
Huntington’s disease
* Neurofibromatosis
* Brachy/Polydactyly
* Familial hypercholesterolemia
* Marfan’s Syndrome
* Achondroplasia
* Progeria
what is PKU?
Deficiency in phe hydroxylase, Phenylacetate accumulation, seizures
* tremors or jerky hand & leg movements
* Hyperactivity, stunted growth
* eczema
* a distinct odor in breath, skin, or urine that is often described as
musty (boiled cabbage)
* Orange urine.
* lighter skin, hair, & eye color than their family members
what is the enzyme phe hydroxylase?
needed to convert essential amino acid phe to tyr
what is Huntington’s disease?
Causes involuntary movements
* caused by a faulty gene for a protein called huntingtin.
Causes degeneration in many regions of the brain & spinal cord
esp. basal ganglia
* If one of your parents is a carrier, you have a 50% chance of
inheriting it.
* Symptoms manifested at middle age
what is cystic fibrosis?
most common lethal genetic disease USA
* caused by a recessive allele carried by about 1/31
Americans of northern European descent.
* Impaired transport of Cl- ions in lung cells
* Does not move Cl- to outside of cell
* Accumulation of thick mucus = Asthma, pneumonia
* Digestive (absorption) problems
* Salty skin, “big” appetite with little/no weight gain
* large greasy stools = malnutrition?
what is Marfan syndrome?
Range of symptoms. Progressive disease
* Disorder of human connective tissue
* Defects of heart valves & aorta = cardiovascular problems= early
death. Chest sinks in or protrudes out.
* Affect lungs, eyes (extreme near sightedness), skeleton, dural sac
surrounding spinal cord
* Tall, long limbs, thin fingers
* Scoliosis
* Flat feet
* Crowded teeth
* Misfolding of protein fibrillin-1
what is brachydactyly?
shortening of fingers and toes
what is neurofibromatosis?
Tumor disorder –Non-cancerous tumors along nervous system. Scoliosis, learning
disabilities, vision disorders & epilepsy.
what is progeria?
Autosomal dominant – accelerated aging
Mutation in lamin A gene
what is incomplete dominance?
F1 hybrids have an appearance between the phenotypes of the two parents
what is not explained by Mendel’s laws?
incomplete dominance, co-dominance, multiple alleles, polygenic inheritance, pleiotropy
what is co-dominance?
both expressed, like a cow with red and white hairs
what is pleiotropy?
one gene affecting multiple traits
what can sickled cells lead to?
a cascade of symptoms like weakness, pain, organ damage, and paralysis
what is an example of multiple alleles and co dominance?
The ABO blood type is controlled by one gene (the ABO gene)
in humans.
– The ABO gene encodes 3 alleles IA(dominant), IB(dominant &
i(recessive)
- Any individual can have only two of the many different alleles for
each trait
what is polygenic inheritance?
the additive effects
of two or more genes on a single phenotype
what are linked genes?
are located close together on a chromosome &
* tend to be inherited together.
what did Thomas hunt morgan do?
used the fruit fly Drosophila melanogaster +
* determined that some genes were linked based on the
inheritance patterns of their traits.
* Contradiction to Mendel’s Law of Independent Assortment
what do sex chromosomes do?
influence the inheritance of certain traits, For example, humans that have a pair of sex chromosomes
designated
* X + Y are male or X + X are female.
what is a gene that is on sex chromosome called?
Any gene located on a sex chromosome is called a
sex-linked gene
where are sex linked genes found and what do they exhibit?
Most sex-linked genes are found on the X chromosome.
* Sex linked genes exhibit unusual patterns of inheritance.
what is colorblindness?
Red-green colorblindness is
– a common human sex-linked disorder &
– caused by a malfunction of light-sensitive cells
in the eyes.
where are sex linked traits more expressed?
more frequently in males than in
females. The gene involved is located exclusively on the X
chromosome.
when is a male color blind versus a female?
A female will be color blind only if she receives the recessive
* color-blind gene on both Xs.
* A male will be color blind if he receives the recessive color-blind
gene on one X chromosome
what is hemophilia?
sex-linked recessive blood-clotting trait that may result in
excessive bleeding & perhaps death after relatively minor cuts &
bruises.
what does recombinant clotting factors help with?
helps alleviate
symptoms
what are sex influenced traits?
Autosomal trait that is expressed differently in males & females
what is an example of sex-influenced traits?
Male pattern baldness.
Is a dominant trait. Expression of trait influenced by testosterone (inherited from mom).
Presence of AR gene greater risk of MPB.
DHT increases hair miniaturization & hair follicles diminish
Old story – MPB – inherited from maternal grandmother
DHT has less effect on women
2. Gout (excess uric acid) – sex influence trait
what are examples of sex linked genes?
color blindness, hemophilia, Duchenne muscular
dystrophy (pronounced as du shern)
