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Genetics and DNA
Transcript of Genetics and DNA
Traits that are carried on either sex chromosome (X and Y) are said to be sex linked. Females have two XX chromosomes, while males have one X and one Y. Males will inherit traits off the Y chromosome but both males and females will inherit traits off the X chromosomes.
Sex Linked Traits
The Y chromosome is shorter than the X chromosome, resulting in some missing genes on the Y chromosome. Males have XY chromosomes, so they are more prone to sex linked traits. This happens because if there is a gene on the X and there is not one on the Y to prevent it from showing up, the child will receive the trait.
These are all possible defects or diesease
Male Pattern Baldness
Duchenne Muscular Dystrophy
Examples of Sex Linked Traits
Punnet squares are used to help predict all possible combinations for the offspring. You can find the ratio of genotypes and phenotypes by using punnet squares. There are two types of punnet squares.
The first type of punnet square has four boxes and is used for monohybrid crosses. A monohybrid cross only involves 1 trait.
EX: Pea color or Plant height
The other type of punnet square has sixteen boxes and is used for dihybrid crosses. A dihybrid cross involves crossing two traits.
EX: Pea color and pea shape, plant height and flower color
Results of Punnet Square Crosses
Alleles control a trait's genotype and phenotype. They are different forms of a trait.
EX: Tall pea plant or small pea plant, round seed or wrinkled seed
The genotype is the letters used to represent the dominant and recessive traits in a punnet square.
While observing pea plants, Mendel created 3 laws that will always be true to genetics, the law of segregation, the law of dominance, and the law of independent assortment.
Mendel’s laws of inheritance.
The law of independent assortment says that the passing of one trait does not affect the other. For example, if you cross a pea plant with green pods and yellow peas with a pea plant with white pods and green peas, the color of the pea pod does not affect the color of the peas.
Law of Independent Assortment
Mendel's law of dominance states that out of a pair of alleles, one allele will be dominant over the other. The dominant trait will be expressed and the recessive trait (the non-dominant trait) will be "hidden" by the dominant trait.
Law of Dominance
Each gamete (which has two alleles) splits in half and the offspring inherits one allele from the mother and one from the father.
Mendel was an Austrian monk who was interested in hereditary, the passing of genes from parents to offspring in plants and animals. His experiments with pea plants laid the foundation for modern genetics. He is called the "father of Genetics".
A gene, also known as a trait, are any characteristics that can be passed from a parent to an offspring. Genes are found on chromosomes of an organism. Organisms tightly pack their DNA in to X shapes called chromosomes. A trait can be homozygous or heterozygous.
Homozygous traits means that there are two identical alleles, either both dominant or both recessive.
EX: BB or bb, YY or yy
A heterozygous trait means that there are two different forms of an allele. There will be only one dominant allele and one recessive allele.
EX: Bb or Yy
A phenotype is the physical appearance of the offspring.
EX: having detached earlobes or attached earlobes
A dominant allele is always shown when present. It will cover up the recessive trait in the phenotype, but the organism will be a carrier for the recessive trait if it is present. A dominant trait is represented by an italicized capital letter.
A recessive allele is not shown when a dominate allele is present. But, when there is no dominant present, the phenotype will show the recessive allele. Recessive alleles are represented by an italicized lower case letter.
In Mendel's experiments, he worked with traits that only had two alleles, such as purple or white flower color. Multiple alleles are traits that have 3 or more different variations. The best example of multiple alleles is blood type in humans. There are four different blood types, A, B, AB, and O. (http://www.discoveryeducation.com/)
Another example of codominance also deals with human blood type. When a person receives an allele for blood type A and an allele for blood type B, the person will have a blood type AB. A and B are both dominant, so both are expressed in the phenotype.
Punnet squares can be used to find the ratio of possible genotypes or phenotypes.
Dihybrid Cross Results
The most common ratio for phenotype from a heterozygous Dihybrid cross is 9:3:3:1.
This means that there was 9 seeds that will have both dominant phenotypes, 3 seeds with dominance for shape and recessive for color, 3 seeds with recessive shape and dominant color and 1 seed that has both recessive traits
Dominant: Yellow color and Round shape
Recessive: Green color and wrinkled shape
Monohybrid Cross Results
The most common ratio for phenotype from a heterozygous monohybrid cross is 3:1.
This means that there will be 3 seeds that have a dominant phenotype and one that will have a recessive phenotype.
Dominant: Purple color
Recessive: White color
For example, when a white cow mates with a redish brown cow, the offspring will be white and red spotted. The white and red are both dominant, so both traits are expressed.
"Incomplete dominance is when two alleles for a given trait are both partially expressed."For example, let's say you have a pea plant with white flowers and a pea plant with red flowers. When the pea plants are crossed, the offspring will be a mix of the two colors, white and red. The offspring will have pink flowers.
DNA is in the form of a double helix. It is made of four bases, adenine(A), guanine(G), thymine(T) and cytosine(C). Adenine and thymine can only bond with each other and guanine and cytosine can only bond together. The back bone of DNA is made up of 5 carbon sugar and phosphate groups.
DNA and Protein
DNA is the instructions in an organism that tells every thing what to make and how it will function. An organism's traits are found in its DNA. DNA strands are located in a cell's nucleus. DNA stand for DeoxyriboNucleic Acid
RNA is a copy of DNA that helps code amino acids to make proteins. RNA is found in the nucleus and the cytoplasm. RNA stands for ribonucleic acid. There are three types of RNA that help in protein synthesis, mRNA, rRNA, and tRNA.
Transcription vs. Translation
There are 3 main differences between DNA and RNA...
1. DNA is made of two strands bonded together into a "double helix". A double helix looks like a twisted latter. RNA is only one stranded.
2. DNA is made of the sugar, deoxyribose, hence the name deoxyribose nucleic acid. RNA, on the other hand, is made of the sugar ribose, hence the name ribonucleic acid.
3. DNA is composed of 4 chemical bases, adenine, thymine, cytosine, and guanine. RNA however, has uracil (U) instead of thymine. In DNA, adenine bonds to thymine, similarly, uracil bonds to adenine in RNA.
DNA vs. RNA
Transcription is when DNA is being copied to form RNA. Translation is when RNA is being decoded to order amino acids to form proteins.
Transcription is when DNA is copied to make RNA. This happens when RNA polymerase attaches to the DNA bases and matches bases to each other making a strand of RNA.
RNA is in the form of a single helix. It is made of four bases, adenine(A), guanine(G), uracil (U) and cytosine(C). Uracil replaces thymine in RNA, but it can still bond with adenine. Guanine will still only bond with cytosine. The back bone of RNA is also made up of 5 carbon sugar and phosphate groups.
DNA is split into groups of 3, called codons. Each codon is the code for an amino acid. Multiple amino acids are combined by peptide bonds to make proteins.
It starts off with the DNA being unzipped by DNA helicase. The point where the helicase is breaking the bonds is called a replication fork.
DNA must replicate itself when it comes time for cell division. This process can happen really quickly. Scientists have named each end of the DNA based on the location of the sugars in its back bone. One end will be 3' (read as 3 prime) and the other end will be 5'. DNA is anti-parallel, meaning one strand will go in a 5'-3' direction the other will go in a 3'-5' direction.
Protein synthesis is the creation of proteins.
RNA polymersase uses DNA as a template to build a strand of mRNA. (transcription)
mRNA takes the code for order of amino acids to the ribosomes. The ribosomes are made by rRNA.
tRNA carries amino acids to the ribosomes. tRNA determines the sequence of amino acids in the protein
The code from mRNA tell the tRNA how to sequence the amino acids. These amino acids are bonded together by peptide bonds. These create proteins. (Translation)
As DNA helicase is unzipping the DNA, DNA polymerase will attach the correct bases to the strands. A will bond with T and G will bond with C.
DNA polymerase can only attach bases starting at the 3' (read as 3 prime) end. This will cause the new side of the DNA strand to be in a 5'-3' direction. This strand is called the Leading strand because bases can be continuously attached.
The other strand is called the lagging strand. This strand starts at 5', so DNA polymerase is not able to continuously add bases. It has to add bases then jump forward again, then keep working, then jump forward again. These chunks of bases are called okazaki fragments.
These okazaki fragments are then bonded together by DNA ligase, to create one continuous strand of DNA.
3 Types of RNA
mRNA, rRNA, and tRNA
mRNA (messenger RNA):
carries the genetic information that was copied from the DNA to the ribosomes
tRNA (transfer RNA):
carries amino acids to ribosomes and attaches them in the order coded in the mRNA
This video will help explain DNA replication to help you understand this process!
rRNA (ribosomal RNA):
associates with proteins to create ribsomes
Here is a video to help describe protein synthesis, starting with transcription, then translation
Transcription is when mRNA is used to code the sequencing of amino acids to form proteins.
Law of Segregation
The law of segregation states that...
For example, lets say you have a parent who is heterozygous Dd and the other parent is homozygous dominant, DD. The offspring will each receive one allele from the parent 1 and another allele from parent 2.
Some time in the future...
For example, purple flower color (B) is dominant over white flower color (b) when dealing with pea plants. If one of the offspring is heterozygous, Bb, then the pea plant will have purple flowers because the purple flower color is dominant over the white flower color.
"Every body have their projects today?" my teacher asked. He is the most fun teacher in the school. Everyone loves him. "Who is willing to present first? They will get extra credit for volunteering!"
"Good! Now who should I pick? " He looked around the class room and his eyes found his favorite student Griffin. "Griffin, you can present first." I watched Griffin strut up to the front of the room. "I did my science project on Genetics and DNA. " " Good! I was hoping someone would choose that! Go ahead and start"...
"Fantastic Griffin! You project looks great! A+! Okay, who's next?"