Chapter 19 Medelian Genetics Flashcards
Law of Segregation
When gametes are made, the two traits carried by each parent separate.
Parent = Aa
Gamete = (A) (a)
Law of Dominance
Dominant gene over recessive
AA crossed with aa only expresses dominant trait.
Law of Independent Assortment
Genes located on different chromosomes assort independently of each other.
Monohybrid Cross
Tt x Tt = ?
1 : 2: 1 genotype ratio
TT: Tt: tt
Phenotype ratio 3:1 Tall:short
Testcross or backcross
Used to find out if it’s homozygous or heterozygous.
Cross it with homozygous recessive individual.
If we get all same trait the original is homozygous dominant.
If we get a mixed then the original was heterzygous.
Dihybrid Cross
Cross between individuals with two genes.
AaBb.
9:3:3:1 phenotypic ratio F2 generation
Incomplete Dominance
Blended phenotype, neither of the two alleles exerts dominance.
Codominance
Both expressed at the same time.
E.g. AB blood types.
Epistatic Genes
A gene that covers up the expression of another gene in the phenotype.
Pleiotropy
occurs when one gene influences two or more seemingly unrelated phenotypic traits.
Can two heterozygotes give a 2:1 ratio in a Punnett Square?
Yes, if there is a lethal gene. Only AA and 2 Aa.
Polygenic inheritance
Two or more genes contributing to a single trait.
Multiple Alleles
When a gene has more than two given alleles.
ABO blood type.
When the wrong blood type is given
Clumping or agglutination would occur to cleanse the blood to foreign protein.
Y linked traits
Holandric inheritance
X link diseases examples
1) Colour blindness
2) Hemopgilia
3) Duchenne Muscular Dystrophy
Barr Body
1 chromosomes inactivated in the embryonic development by methylation
Autosomal recessive inheritance
Autosomal = non sex linked chromosome
E.g. Cystic fibrosis: Defect in Cl- channel protein, excessive mucus with infections.
Albinism: Absense of melanin
PKU: Unable to metabolize phenylalanine
Affects both sexes equally, can appear to skip generations.
Autosomal Dominant Inheritance
No sex preference, no skipping gens, if you have one affected gene, you have the disease.
E.g Achondroplasia (dwarfism) and Marfan Syndrome (Connective tissue disorder).
2 people heterozygous for an autosomal dominant disorder
Phenotypic ratio 3:1
Genotype ratio 3:1
AA and Aa have the disease
Males give x linked genes to only their ____
Daughters, not sons
A male gets a sex linked disease from his
Mother
Pedigree tips
Determine whether the trait is dominant or recessive: If the trait is dominant, one of the parents must have the trait.
Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait:For example, in X-linked recessive traits, males are much more commonly affected than females. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions).
Linkage and Crossing Over
Linkage could be disrupted when crossing over occurs during meiosis.
The farther apart two genes are on a chromosome, the greater the frequency of crossover and recombination between them.
Chromosomal Abnormalities
Nondisjunction, failure of homologous chromosomes to separate in Anaphase I or II of meiosis.
Wrong number of chromosomes, called aneuploidy.
Chromosomal abnormalities example
Turner syndrome, Kleinfelter syndrome, down syndrome
Turner Syndrome
Female with 1 X chromosome, no bar bodies in this sterile female. Only viable monosomy known in humans.
Kleinfelter Syndrome
A male with XXY, sterile male with feminization
Down syndrome
Extra 21 chromosome, trisomy 21, mental retardation, heart defects, more prone to Alzheimers and Leukemia
Polyploidy
Common in plants (weeds, danelions, and wild oats). 3N or 4N cells. Endosperm of plant seeds are 3N. Human liver cells can be 3N or 4N.
Deletion
Missing gene due to break or fragment lost. Chromosomal deletions are associated with some cancers.
Cri du chat syndrome: short arm of chromosome #5 is deleted.
Duplications
Addition is now added on a chromosome from one that is fragmented. Partial Trisomy results. Radiation, chemicals, or even viruses.
Translocation
Deleted chromosome fragment is joined to a nonhomologous chromosome.
Robertsonian translocation - chromosome 21 long arm onto the long arm of chromo 14.
Amniocentesis
Amniotic fluid of the fetus can be cultured and subjected for karytopic analysis. Fetal secretions and epidermal cells from respiratory and GI tract.
Ultrasound
Fetus is visualized to see any morphological defects prenatally.
CVS (Chorion Villus Sampling)
Sample of placenta is removed. Higher risk than amniocentesis.
How many gametes can be made given the following genotype? Xx Yy Zz WW BB
2n rule, n= number of heterozygotes
