Unit 3 gene part 2 chromosomes and Genes Flashcards
what is a monohybrid cross?
cross of two individuals that differ in one trait
what is a dihybrid cross?
a cross of two individuals that differ in two traits
What does Mendel’s first law state? ( The law of segregation?
Mendel’s law states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete
( all individuals have two copies of each factor.. (genes). These copies segregate (separate) randomly during gamete formation, and each gamete receives one copy of every factor.
Allele
the singular letter present in a genotype is called an allele
capital letter- dominant
lowercase letter - recessive
what is genotype
the from expressed for genes in letter
ex. AAbb or AaBb
what is phenotype
the form to express a trait in physical form.
ex. purple, red
what is the meaning of homozygous?
An organism that has two identical alleles for a trait
ex. RR or rr
what is heterozygous?
an individual with two different alleles for a trait.
ex. Rr
what is the law of independent assortment?
the law that states that genes separate independently of one another in meiosis
( the two alleles for one gene segregate (assort) independently of the alleles for other genes during gamete formation)
what is the law of dominance?
recessive alleles will always be masked by dominant alleles
What is a testcross?
A cross involving the unknown organism with a homozygous recessive organism
If recessive traits show up in the first generation of a testcross then the unknown must have been what?
heterozygous
If nothing but dominant traits appear in F1 and successive generations, then the unknown is most likely what?
homozygous, purebred, true-breeding
What is Type III- incomplete dominance?
The heterozygous genotype yields a third phenotype that is a blending of the dominant and the recessive alleles. Includes color, shape, and severity of disease.
What is Type IV- Codominance?
Hetrozygous genotype yields a third phenotype that is an equal expression of both alleles. Get roan coats, red and white colours, blood Type AB
Type V- Lethal alleles
when gene is homozygous (either dominant or recessive), it can cause death. If lethal allele is dominant, then individual with GG will die. if lethal allele is recessive, then individuals with gg will die.
Creeper chickens, Manx cat, cystic fibrosis, sickle cell anemia
What is the method for writing genotypes for Linked genes ?
Femals and males with a disease inheritance…?
These diseases are only places on the X chromosome thats why they are referred as X-linked inheritance
what is multiple alles?
a gene with more than two alleles
What is X-inactivation inheritance?
- occurs when one copy of the X chromosomes is inactivated
- prevents females from having too many gene products (dosage compensation)
- which X becomes inactive is random during embryonic development
What are autosomal linked genes?
autosomal linked genes are genes that are located on the same chromosome from chromosomes 1 through to 22. They are except from crossing over and tend to be inherited together.
- Defies Mendel’s law of independent assortment
- monohybrid pattern
What are unlinked genes ?
genes located on different chromosomes
- dihybrid pattern
what is the impact of gene linkage?
you loose variety
What are the benefits of gene mapping?
- allow us to understand the overall complexity and genetic organization of a particular species
- improve out understanding of the evolutionary relationships among different species
- used to diagnose, and, someday to treat inherited human diseases
- predict the likelihood that a couple will produce children with inherited diseases
The higher the crossover frequency between two genes, the what???
the further apart they must be on the chromosomes
what is recombinant types ?
F1 generation have different combination of alleles than the chromosomes of the P generation.
what is recombination frequency?
the percentage of times that a crossover occurred as P gametes were formed.
what is the formula for recombination frequency?
Number of recombinant types
__________________ x 100%
Total number of offspring
smaller the crossover rate the _____ the genes are?
closer
What is the pattern of inheritance for Autosomal Dominant
? (Aa OR AA)
- due to a dominant allele carried on one of the autosomes (e.g tongue rollers, widow’s peak)
- affected child has affected parent
- males and females are affected equally
- 2 unaffected parents will not have affected children
- huntington disease- common autosomal dominant disorder
what is autosomal recessive (aa) inheritance pattern?
- due to recessive alleles carried an autosome (e.g attached earlobes, curved thumbs)
- individual must inherit a recessive allele from each parent
- individual will be a “carrier” if they are (Aa)
Cystic fibrosis…
X- linked recessive (X^bY or X^b X^b) inheritance pattern?
- more males than females are affected as they only need one recessive allele
- an affected female has an affected father
- an affected women will have all affected sons
- characteristic often skips a generation from the grandfather to the grandson
ex. Hemophilia
X-linked dominant ( X^BY, X^BX^B, X^BX^b) inheritance pattern?
- rarest of all inheritance types
- gene on the X chromosome so no transmission from father to son
- affected males produce affected females
- since females have 2x chromosomes they are more likely to be affected
X-linked dominant disorders are not very common
who was Fredrick Griffith?
Proved a process called transformation: genetic material from one cell can be transferred to another cell.
Oswald Avery
Discovered that the nucleic acid in DNA stores and transmits genetic information from one generation of bacteria to the next.
who is Alfred Hershey and Martha chase ?
used radioactive markers in experiments to show that DNA was the genetic material in cells
Ervin Chargaff
defined the rule that the %A=%T and %G=%C in all double stranded DNA genomes
Rosalind Franklin
Woman who generated x-ray images of DNA, she povided Watson and Crick with key data about DNA
-Used X-ray diffraction to discover the double-helical structure of DNA.
- she concluded that the nitrogenous bases were located on the inside of the helical structure, and the sugar-phosphate backbone was located on the outside, facing toward the watery nucleus of the cell.
What does it mean when DNA strands are Antiparallel?
Strands parallel to each other going in opposite directions (3’-5’ and 5’-3’)
What are the three components of a nucleotide?
- phosphate base
- deoxybrose sugar
- nitrogen base (a,t,c,g)
what is a double helix?
two strands of nucleotides wound about each other; structure of DNA
what is RNA and how does it differ from DNA?
- It is still found in the nuclei like DNA but has three key differences:
1. the sugar componenet of RNA is ribose rather than deoxyribose.
2. RNA does not have the nucelotide thymine (T) in its place is the nucleotide uracil (U).
3. RNA remains single stranded, although the single stand can sometimes fold back on itself to produce regions of complementary base pairs
What is the first step of DNA replication and what happens during this process?
the first step is called helicase:
- A group os enzymes called helicases, bind to the DNA at the replication origin. The helicase breaks the H-bonds between N-bases and creates a Y-shaped areas called replication forks.
- unwinding or unzipping DNA.
What happens during the DNA molecule during the second step of DNA replication?
DNA polymerase
base pairs the
exposed N-bases in
the leading
continuous strand
(5’ to 3’) and the
lagging
discontinuous strand
(Okazaki 3’ to 5’
fragments)
What happens during the third step of DNA replication?
Ligase adds the
deoxyribosephosphate backbone
completing the
polynucleotide DNA.
Proofreader
enzymes check for
mismatched pairs
and correct
58 Draw out Semi-conservative
what is a codon?
3 consecutive N-bases, codes for one amino acid pairing
What happens during transcription? (this is seen when converting DNA to protein)
- this takes place in the nucleus
- how?:
1. one DNA stand acts as the sense strand. This is the code for the gene. Therefore, to express the correct gene, the DNA is read 3’ to 5’
2. RNA polymerase base pairs those in the RNA molecule using the antisense strand (DNA STRAND). The mRNA is transcribed in the 5’ to 3’ direction
3. Phosphates and sugars are added to complete the mRNA
Explain mRNA processing?
Before mRNA can leave the introns (useless sequences of nitrogen bases), must be removed. Enzymes, called restriction enzymes, perform this task. Exons (useful sequences of N- bases) are then spliced together using ligase enzymes. We now have a fully functioning mRNA capable of making proteins.
What is initiation (first step of translation)?
- AUG start codon; ribosome reads the mRNA in the 5’ to 3’ direction
- mRNA is attached to a subunit of the ribosome, the first codon is always AUG
What is elongation (step two of translation)
Addition of amino acids connected together by strong peptide bonds for entire length of the mRNA; tRNAs bring in the proper amino added to the growing polypeptide chain.
What is termination (still step 2 of translation) ?
occurs when a stop codon in the mRNA reaches the A site of the ribosome
- stop codons; stops protein synthesis; at end of the gene code for this trait
