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alleles of a gene, genetic
Segregation: two members of each gene must segregate into different gamete cells during the formation of eggs and sperm in the parents
independent assortment – alleles of different genes transmitted independently of one another
Incomplete dominance –
heterozygotes have intermediate phenotype (polymorphism)
heterzygotes have phenotypes of both alleles
Gene-by-gene interactions –
in discrete traits, phenotype associated with an allele depends on which alleles are present at another gene (one allele can be associated with different phenotypes)
Gene-by-environment interaction –
phenotype influenced by environment experienced by individual (same genotypes can be associated with different phenotypes)
Polygenic inheritance of quantitative traits –
many genes are involved in specifying traits that exhibit continuous variation ( unlike alleles that determine discrete traits, each allele adds a small amount of phenotype
Explain how the structure of DNA explains how it functions as THE hereditary molecule.
- DNA made of monomers called deoxyribonucleotides (deoxyribbose moleceule, phosphate group, and a nitrogenous base).
- Has (1) backbones made up of the sugar and phosphate groups of deoxyribonucleotides and (2) a series of nitrogen-containing bases that project from the backbone.
- One end has a 3’ carbon of a deoxyribose, while one has exposed phosphate group on 5’ carbon.
- Strands line up antiparallel, into double helix
- Strands of DNA serve as templates for the production of new strands, with bases being added to the new strands according to the complementary base pairing.
Describe the basic steps involved in DNA replication in both prokaryotic and eukaryotic cells.
- DNA polymerase can add deoxyribonucleotides to only the 3’ end of a growing DNA chain. As a result, DNA synthesis always proceeds in the 5’ -> 3’ direction (of new strand)
- Prokaryotic chromosomes have a single origin of replication buble tha proceeds in both directions
- Eukaryotic chromosomes have multiple origins of replication
- Helicase breaks hydrogen bonds between nucleotides and unzips the enzyle, single-strand DNA-binding proteins (SSMPs) attach and separate the strands to prevent them from bonding back together.
- Topoisomerase cuts DNA and allows it to unwind, relieving stress
- Primase makes a short stretch of RNA for primer for DNA polymerase, which then begins to add deoxyribonucleotides to the 3’ end of it, producing a new complementary strand. Sliding clamp holds it in place (LEADING STRAND SYTHESIS)
- Lagging strand leads away from replication fork.
- Primase synthesizes a short stretch of RNA as primer, then DNA polymerase III adds bases to the 3’ end of the primer. DNA polymerase synthesizes short fragments of DNA (okazaki fragments) that are later linked together to form a continuous strand by DNA ligase.
Explain how errors in DNA replication can happen and are corrected.
- DNA polymerase III can proofread, if the wrong base is added durning DNA synthesis, the enzyme removes the mismatched base that was added, and proceeds with synthesis
- Mismatch repair – if DNA polymerase leaves a mismatched pair, enzymes remove a section containing the incorrect base, and fill in the correc bases using the old strand as a template
- UV light, radiation, chemical attack, or other events can cause damage, cells have a wide arry of damage repair systems
- Nucleotide excision repair – enzymes remove segment of DNA containing defective sequence, and synthesis of a correct strand done.
Silent mutation –
change in nucleotide does not change amino acid specified by codon,, change in genotype but no change in phenotype. Neutral
change in nucleotide changes amino acid specified by codon, change in phenotype and structure of protein. Beneficial, neutral, or deleterious
changes in nucleotide that results in early stop codon, premature termination, usually deleterious
addition or deletion of a nucleotide, reading frame is shifted and massive missense, change in phenotype, usually deleterious
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