Mendelian Inheritance Flashcards
Gregor Mendel
An Austrian monk who conducted breeding experiments with the garden pea. He formulated fundamental laws of heredity in the early 1860s without knowledge of cells or chromosomes and without a microscope.
Dominant Characteristics
Traits that are more likely to be inherited because they are expressed in heterozygous or dominant homozygous alleles. (It is written in capitals. In AA or Ab, A is dominant and will be expressed).
Recessive Characteristic
Less common traits that are only expressed when an organism has two recessive alleles for that trait. (It is written in lower-case. In Ab, b is recessive and won’t be expressed, but it will be expressed in bb).
Homozygous alleles
Inheriting identical version of genes from each parent (e.g., AA or bb)
Heterozygous alleles
Inheriting two different versions of the same gene from each parent (e.g., Aa or Bb)
Blending
A theory present before Mendel. It stated that parents of contrasting appearance produce offspring with intermediate appearance. (A red and white flower will make a pink flower).
Particulate theory of inheritance
Mendel’s theory. Inheritance involves reshuffling genes from generation to generation. Traits are passed down in genes and these genes can be dominant or recessive.
monohybrid cross
Breeding two different plants that differ in only one trait. (e.g., breed one tall pea plant and one short pea plant)
True-breeding
Breeding plants that are homozygous for a certain trait.
P
Parental generation (the first plants that are bred)
F1
First filial generation offspring. (The second plants that are bred. They are the offspring of P)
F2
Second filial generation of offspring (The third round of plants that are bred. They are offspring of F1)
Breakdown of Mendel’s first monohybrid cross
Used two different true-bred plants that different in only one trait, and bred them. He then bred the offspring to get another generation.
Law of segregation (4 parts)
- Each individual has a pair of alleles for each trait
- The alleles segregate during gamete (sperm and egg) formation
- Each gamete contains only one allele from each pair
- Fertilization gives the offspring two factors for each trait.
Alleles
A version of the same gene. (e.g., an allele for blue eyes or an allele for green eyes). They occur on the homologous pairs of chromosomes at a particular locus
Locus
Location on a chromosome
Genotype
Refers to the two alleles an individual has for a specific trait. (e.g., AA or bb)
Phenotype
The physical appearance or trait of the individual that is a result of the genotype (e.g., blue eyes)
Punnett Square
Table listing all possible genotypes resulting from breeding
Dihybrid cross
Uses two different true-breeding plants that differ in two traits. (A tall green pea plant is bred with a short brown pea plant)
Law of independent assortment (2 parts)
The pair of alleles for one trait segregate independently of the alleles for other traits. (think of independent assortment in meiosis!!)
All possible combinations of alleles can occur in the gametes.
Factors
What Mendel called alleles.
The dihybrid cross led to…
the formation of the law of independent assortment
The monohybrid cross led to…
the formation of the law of segregation
Incomplete Dominance
Heterozygote has phenotype in the the middle of homozygous parents. (red and white flowers make pink flowers)
Multiple Allelic Traits
A trait that exists in several allelic forms, but everyone only has 2 alleles. (Aa and Cc both make blue eyes, but you can only have Aa or Cc)
“A” blood type
Phenotype is either AA or AO. Expressed with IAIA or IAi genotype
“B” blood type
Phenotype is either BB or BO. Expressed with IBIB or IBi genotypes
AB blood type
AB phenotype and expressed with only IAIB genotype
O blood phenotype
Phenotype is OO and expressed with ii
IA blood allele
A antigen on red cells, anti-B antibody in plasma. Dominant allele
IB blood allele
B antigen on red cells, anti-A antibody in plasma. It is a dominant allele
i blood allele
Neither A or B antigens, and has both antibodies. It is recessive
Polygenic Trait
When a trait is governed by two or more genes with different alleles. Each allele has an effect on the phenotype, and each allele adds up to get the final phenotype. (A genotype could be AaBBCcddEe)
Bell-shaped/normal curve
The shape of a graph that displays the distribution of polygenic traits
Pleiotropy
A gene that affects more than one characteristic. (Sickle-cell trait alters your blood cell shape AND prevents you from malaria)
Codominance
More than one allele is fully expressed. (A black cow breeds with a white cow, and they get a black and white striped cow)
Epistatis
A gene at one locus interferes with the expression of a gene at a different locus.
(if your melanin production gene doesn’t work, then it doesn’t matter what genes you have for skin color; you will be albino).
Himalayan rabbit ice pack experiment
A rabbit had a icepack placed on it’s back, and when frozen it’s fur turned from black to white.
This emphasizes that the environment can effect the phenotypes.
