Lecture 9 pt 1 &2: foundation of genetics, mendal's Law, and heredity Flashcards
What is genetics?
the study of heredity, genes, and genetic variation in organisms.
What is heredity?
The passing of genetic information from one generation to the next
What is a trait?
a heritable feature.
What was Gregor Mendel experimental setup?
-Step 1. creating true-breeding by self-fertilization: Mendel used true-breeding plants that consistently produced offspring with the same traits when self-fertilized.
-Step 2. Hybridization: he crossed two true-breeding plants that had contrasting traits (purple and white) to create F1 generation.
-Step 3. Creating the F2 generation: Mendel allowed the F1 generation to self-fertilize, producing the F2 generation.
-Observations: In the F2 generation a 3:1 ration of dominant to recessive traits showed.
what are Mendels laws?
-1st law of segregation
-2nd law of independent assortment
What is mendel’s first law of segregation?
Each individual has two alleles for each gene and these separate from each other during the formation of gametes. One gamete gets one gene, the other gamete gets the other. During fertilization, the offspring will end up with two alleles, one allele from mom, one allele from dad.
What is the law of independent assortment?
Genes located on different chromosomes are inherited independently of one another. The inheritance of one gene does not affect the inheritance of another gene because during meiosis, homologous chromosomes line up and separate randomly, so there is no way of knowing if two genes will cross or separate therefore genes on different chromosomes do not influence each other when forming gametes.
What is a gene?
The segment (block) of DNA that codes for a specific protein which is expressed by a certain trait. It stores genetic information and is the basic unit of heredity.
What is an allele?
a version of a gene with one allele from each parent. Alleles are alternative formations of genes.
What is a phenotype and a genotype?
the observable physical traits of an individual. Genotype is the genetic makeup of an individual.
What is homozygous and heterozygous?
Homozygous is when two alleles are either both recessive or both dominant
Heterozygous is when one allele is recessive and the other is dominant.
What is a dominant trait and dominant allele?
-Dominant trait: is the trait that appears in the F1 generation
-Dominant allele: The allele that will only show up in the phenotype
What is recessive trait and recessive allele?
-recessive trait is trait that doesn’t appear in the F1 generation
-Recessive allele is the allele that will only show up in the phenotype is the dominant allele is not in the genotype.
What is a punnet square? How do you set one up?
A way to predict the genotypes of a particular genetic cross
To set up a punnet square:
-establish the genotypes of the parents
-place one parent on top, the other on the side
-fill in the punnet square
What is a test cross?
used to predict an individuals genotype particularly when an individual expressing a dominant phenotype has an unknown genotype. It involves the crossing the unknown individual with a homozygous recessive individual.
What is a dihybrid cross?
A dihybrid cross examines the inheritance of two traits simultaneously, such as seed shape (round vs. wrinkled) and seed color (yellow vs. green).
The results can be analyzed to determine the phenotypic ratios of the offspring, such as tall with axial flowers, tall with terminal flowers, etc.
List some traits that do not follow mendelian inheritance.
-continuous variation
-epistasis
-pleiotrophic effects
-incomplete dominance
-codominance
-Enviromental effects
-Epigenetics
What is continuous variation?
Traits like height that are Polygenic meaning Multiple genes control a phenotype
What is Pleiotrophic effects?
Where An allele that has more than one effect on a phenotype with examples like cystic fibrosis and sickle-cell disease.
What is incomplete dominance?
where alleles are not fully dominant or fully recessive
-ex. red and white flower cross to make a pink flower
What is codominance?
Where both alleles are expressed, such as a horse with both white and black hairs.
What are environmental effects?
The degree to which many alleles are expressed depends on the environment
-ex. Arctic foxes only produce fur pigment when the temps are warmer
what is epistasis?
An interaction between two genes where one of the genes modifies the phenotypic expression produced by the other.
-ex. pigment production in dogs
What is Epigenetics?
Changes in a phenotype without changing the DNA sequence
What is the chromosomal theory of inheritance?
The chromosomal theory of inheritance states that chromosomes are the material of inheritance and genes assort independent because they are located on the chromosomes that assort independently during anaphase l
what are sex-linked traits?
traits that are determined by genes located on sex chromosomes.
-ex. colorblindness
What is linkage?
Linkage is the tendency of genes that are close together to be inherited together.
What is nondisjunction?
Failure of chromosomes to separate correctly during meiosis 1 or 2. It can lead to an abnormal number of chromosomes which is called aneuploidy which is lethal.
What type of conditions are a result of nondisjunction?
-Down syndrome: having an extra copy of chromosome 21
Nondisjunction of sex chromosomes is also discussed, leads to conditions like:
-XXX female (triple X): Generally taller than average.
-XXY male (Klinefelter syndrome): Sterile male with many female characteristics and diminished mental capacity.
-XO female (Turner syndrome): Sterile female with webbed neck and diminished stature.
-XYY male: Fertile males of normal appearance.
What are chromosomal structural rearrangements?
Changes in the structure of a chromosomes caused by break in DNA that get repaired incorrectly.
What are some examples of chromosomal structural rearrangements?
- Deletion: piece of chromosome is lost
-ex. Cri-Du-chat small arm of chromosome 5 is deleted - Duplication: portion of chromosome is copied
-ex. down syndrome - Reciprocal translocations: the exchange of segments between 2 non-homologous chromosoems
- Inversion: segments of chromosome that breaks off, flips, and reattaches in reverse order. Pericentric inverse includes the centromere and paracentric does not include the centromere
- Insertion: a segment form one chromosome is inserted into another non-homologous chromosome.
What is a pedigree?
Determine whether a trait is sex-linked or autosomal and used to determine whether the traits phenotype is dominant or recessive.
What are mutations?
accidental changes in genes, which Rarely occur and Usually involve recessive alleles.
What are genetic disorders?
diseases caused by mutant alleles (genes).
What is common recessive traits?
-common baldness
-albinism
-alkaptonuria: inability to metabloize homogentistic acid
-red-green colorblindness: inability to see red and green wavelengths of light
What are common dominant traits?
-Mid-digital hair: presence of hair on middle segments of fingers
-Brachydactyly: short fingers
-Comptodactyly: in ability to straighten the little finger
-polydactyly: extra fingers and toes
What is sickle cell disease?
Recessive heredity disorder where red blood cells are misshapen and can block blood flow, leading to various health complications
What is Hemophilia?
recessive blood-clotting disorder, sex-linked and famously associated with queen Victoria
What is Tay-sachs disease?
recessive allele that is incurable which causes the brain to deteriorate. suffered rarely live beyond five years of age.
What is Huntington’s disease?
dominant allele that causes the deterioration of brain cells. does not develop til 30 yrs or older
What is genetic counseling?
provides information and support to parents at risk of producing a child with genetic defects
What is genetic screening?
identify carriers of genetic disorders. it is used to allow the prenatal diagnosis of high risk pregnancies.
What are genetic screening techniques?
-Amniocentries: doctors obtain amniotic fluid to test fro specific genetic disorders and genetic defects
-ultrasound: observing fetus
-Chorionic Villis sampling: removal of fetal cells from placenta fro analysis
What are analysis of fetal cells?
-chromosomal karyotype: reveal aneuploicly or chromosomal alternations
-enzyme activity: test for proper functioning of enzymes associated with genetic disorders
-genetic markers: test for the presence of mutations
What is DNA screening?
blood analysis test to analysis genetic conditions in baby
also includes the preimplantation genetic screening (in vitro fertilization)
