Genetics- Chapter 5 and 6 Flashcards
Gregor Mendel
- “father of inheritance”
studied inheritance in pea plants
Why did Mendel study Pea Plants?
- they produce quickly and in large numbers
- matured quickly
- showed many traits with only 2 variations (e.g. tall or short, yellow or green)
Gene
- Sections of DNA that have instructions for a specific trait
- Comes in alternate forms called alleles
Alleles may be…
Dominant or Recessive
Define dominant and state what letter it is represented as
Dominant- codes for a trait that is ALWAYS expressed “shows up”
- represented as an uppercase letter
Define Recessive and state what letter it is represented as
codes for a trait that is usually hidden “masked by a dominant gene”
- represented by a lower case letter
True Breeding
only making an offspring of their kind either by self fertilization or crossing with another of their kind
Cross
mating between 2 individuals
Monohybrid Cross
a cross designed to study the inheritance of only one trait
P Gen
The parent plants used in a cross
First Final or F1 Gen
the offsprings of the P Gen cross
Law of Dominance
When individuals with offspring traits were crossed, the offspring will always express the dominant trait
F2 Gen
Offsprings of the F1 cross
Law of Segregation
1) organisms inherit two copies of genes, one from each parent
2) organisms donate only one copy of each gene to their gametes because the genes separate during gamete formation to give offspring 1 allele
Phenotype
“physical”; describes how genes are expressed (aka what shows up
e.g. tall or short
Genotype
“gene”; describes genetic makeup
e. g. AA, Aa, aa
* may be heterozygous or homozygous
Homozygous
2 of the SAME copies of a gene
e.g. AA or aa
Heterozygous
2 DIFFERENT copies of a gene
e.g. Aa
Test Crosses
crossing an individual with an unknown genotype with a homozygous recessive individual
- phenotypes of the resulting offspring may indicate the genotype of the unknown
Pedigrees
illustrates the inheritance of a trait among a group of related individuals
- useful when following a harmful trait, or dog breeding
Pedigree Symbols
square- male
circle- female
shaped square and circle- have traits
straight line joining 2 symbols- mating or married
horizontal line- line of descent
straight line that drops to 2 shapes- siblings or offsprings
Incomplete Dominance
neither allele dominates the other instead both influence each other; results in partial expression of both traits
e.g. red + white = red, white and pink
Codominance
Both alleles for a trait are equally dominant. results in a phenotype that shows both homozygous phenotypes
e.g. red hair cows (RR) + white hair cows (WW) = Roan (RW); cows with both red and white hairs
Blood types and their pheno and geno types
Phenotype: Genotype:
A AA or AO
B BB or BO
AB AB
O OOComplete Dominance
Complete dominance over the recessive allele
e.g. Rr
Key info on Sex- Linked Inheritance
Males only have 1 X chromosome and their Y isnt homologous. therefore men can only have 1 X chromosome ( this is called Hemizygous)
Sex- Linked Inheritance
describes an allele that is found on one of the sex chromosomes either X or Y that is expressed when passed onto teh offspring
Barr Body
a single inactive X chromosome
Multitrait Inheritance
the affect one inheritance trait can have when crossed with another
e.g. crossing round (R) and yellow (Y) seeded plants with a wrinkled (r) and green (y) seeded plant
Law of Independent Assortment
The inheritance of one trait does not affect the inheritance of another
- except if genes are linked
Product Law
the probability of 2 or more events occurring together is the product (multiply) of their individual probabilities
e.g. RrYy x RrYy = Rr x Rr and Yy x Yy
2 types of Variation
Discontinuous Variation- trait is determined by activity of one gene and produces “clear cut” phenotypes
e.g. tall or short
Continuous Variation- Trait is determined by activity of multiple genes (polygenic) and produces a range of phenotypes
e.g. human height and skin colour
List the 5 people and or groups and what they discovered about DNA
- Meisher- isolate the substance found in the nucleus, called it the nuclein
- Hershey and Chase- confirmed that DNA contained heredity information not proteins
- Levene- discovered chemical composition of DNA, made of a building block called a Nucleotide, which has 3 parts:
- a sugar
- a negatively charged phosphate group
- 1 of 4 nitrogen bases; Adenine, Guanine, Cytosine and Ihymine - Chargaff- found that the amounts of A and T were always equal in a sample of DNA and so were C and G
- Watson and Crick- determined that DNA exists as a double helix “twisted ladder”
DNA Structure
- always has a complementary base; A with T and C with G
- ladder analogy; sides made of alternating squares and phosphates, steps were made of nitrogen base pairs
Mutation
change in the sequence (order) of nitrogen bases in the DNA
- this can happen in interphase during DNA replication
- semi conservative; each new molecule of DNA has half of the original molecule
can be spontaneous: occur without specific cause
can be induced: caused by exposure to hazardous chemicals, radiation, and viruses
- only heritable if it occurs in the production of gametes
Result of a mutation can be….
positive- helpful to an individual (ie lactose intolerant)
negative- harms the individual (ie genetic disease where we cant make protein to to fight it off)
neutral- has no impact (ie change doesnt affect protein or it occurs in areas of DNA without genes
First type of Mutation
Point Mutation: small change in DNA, several or few bases are changed
- Base Pair substitution: one bp is switched with another
- Frameshift Mutation: a base pair is added or deleted
second type of mutation
Chromosomal Mutation: large change in DNA, affects 100s or 1000s of bp
- inversion: chunk of chromosome is removed and reinserted backwards
-translocation: extra chunk of chromosome is attached to another chromosome
deletion:chunk of chromosome is lost
duplication- chunk of chromosome is repeated
Human Genotype Project
began in 1990, with goal to identify the sequence (order) of the entire 3 billion nitrogen base pairs in human DNA
Non-Coding DNA
- About 2%
- contains actual genes that can be used to make proteins
Coding DNA
- About 98%
- does not contain genes, some is functional (regulates gene activity) and some is non-functional
