GENETICS Flashcards
study of heredity
Genetics
set the framework for genetics long before chromosomes or genes had been identified, at a time when meiosis was not well understood. He
selected a simple biological system and conducted methodical, quantitative analyses using large sample
sizes.
Johann Gregor Mendel
Mendel‘s seminal work was accomplished using the garden pea, _________ , to study inheritance. This species naturally selffertilizes, meaning that pollen encounters ova within the same flower.
Pisumsativum
mating two true-breeding individuals
that have different traits. (Pea can self fertilized)
Hybridizations
• P - Parental generation - are all parents are color white?
• F1 Generations - Filial 1 - produce 705 white pea plants
• F2 Generations - Filial 2 - 224 are violet peas
• etc.
- reduction division; reduce parents by dividing haploid
Meiosis
- defined as a variation in the physical appearance of a heritable characteristic.
Trait
- a paired cross in which the respective
traits of the male and female in one cross become the respective traits of the female and male in the other
cross.
Reciprocal cross
- those that are inherited unchanged in
a hybridization.
Dominant traits
- becomes latent, or disappear in the
offspring of a hybridization.
Recessive traits
- the observable traits expressed by an
organism. (Examples: skin color, curly/wavy hair, etc.)
Phenotype
- an organism‘s underlying genetic makeup, consisting of both the physically visible and the non-
expressed alleles. (Example: behavior, ability, and other characteristics.)
Genotype
are physical expressions of traits that are transmitted by alleles. Capital letters represent dominant alleles and lowercase letters represent recessive alleles. The phenotypic ratios are the ratios of visible characteristics.
Phenotypes
The genotypic ratios are the ratios of gene combinations in the offspring, and these are not always distinguishable
in the phenotypes.
- expressed unit factor
Dominant Allele
- latent unit factor
Recessive Allele
Mendel‘s _______ states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. For example,
when crossing true- breeding violet-flowered plants with true-breeding white- flowered plants, all of the offspring were violet flowered, even though they all had one allele for violet and one allele for white.
Rather than both alleles contributing to a phenotype, the dominant allele will be expressed exclusively. The recessive allele will remain latent, but will be transmitted to offspring in the same manner as that by which the dominant allele is transmitted. The recessive trait will only be expressed by offspring that have two copies of this allele and these offspring will breed true when self-
crossed.
The allele for albinism, expressed here in humans, is recessive. Both of this child‘s parents carried the recessive allele.
law of dominance
is a chart that allows you to easily
determine the expected percentage of different genotypes in the offspring of two parents.
Punnett square
states that paired unit factors (genes) must segregate equally into gametes such that offspring have an equal likelihood of inheriting either factor.
Law of Segregation
The dominant-expressing organism is crossed with an organism that is homozygous recessive for the same
characteristic.
Test Cross
One of the alleles appears in the phenotype in the heterozygote, but not to the exclusion of the other, which can also be seen.
Incomplete Dominance
Both alleles for the same characteristic are simultaneously expressed in the heterozygote.
Codominance
Exist at the population level, such that many combinations of two alleles are observed.
Multiple Alleles
Blood types:
• A - negative 6%
• O - negative 7%
• B - positive 11%
• A - positive 32 %
• O - positive 40%
Rarest blood types:
• AB - negative 1%
• B - negative 2 %
• AB - positive 4 %
A - Can receive only from A,O
Can give to AB, A
AB - Universal recipient.
Can only give to AB.
B - Can receive only from B, O
Can only give to AB, B
Blood type O - universal donor.
Can receive only from blood type O
also referred to as Hardy-Weinberg Principle, is used to compare allele frequencies in a given population over a period of time.
Hardy-Weinberg Equilibrium
A population of alleles must meet five rules in order to be considered “in equilibrium”.
5 rules:
1. No gene mutations may occur and therefore allele changes do not occur.
2. There must be no migration of individuals either into or out of the population.
3. Random mating must occur, meaning individuals mate by chance.
4. No genetic drift, a chance change in allele frequency, may occur.
5. No natural selection, a change in allele frequency due to environment, may occur.
Handy-Weinberg Equilibrium never occurs in nature because there is always at least one rule being violated.
Handy-Weinberg Equilibrium is an ideal state that provides a baseline against which scientist measure gene
evolution in a given population.
The Handy-Weinberg Equilibrium can be used for any population; the population does not need to be in
equilibrium.
