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Genetics and Evolution - Biology

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Genetics and Evolution - Biology genes ️physical and biochemical characteristics of every living organism is determined by genes, which are DNA sequences that code for heritable traits that can be passed from one generation to the next chromosomes ️all genes are organized into chromosom...

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  • August 3, 2024
  • 16
  • 2024/2025
  • Exam (elaborations)
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  • genetics and evolution biology

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Genetics and Evolution - Biology
genes ✔️physical and biochemical characteristics of every living organism is determined by genes,
which are DNA sequences that code for heritable traits that can be passed from one generation to the
next



chromosomes ✔️all genes are organized into chromosomes, to ensure that genetic material is passed
easily from daughter cells during mitosis and meiosis



alleles ✔️each gene has alternative forms called alleles. I.e. IA IB and i for blood



genotype ✔️genetic combination possessed by an individual is known as genotype



phenotype ✔️manifestation of given genotype as an observable trait is known as phenotype



homologues ✔️each human possesses two copies of each chromosome called homologes except for
male sex chromosomes (only one X chromsome and one Y chromsome)



locus ✔️each gene has particular locus, or location on a specific chromosome. Normal locus of a
particular gene is consistent among human beings such that a gene can be descried by its location



dominant ✔️alleles can be categorized based on their expression. If only one copy of an allele is
needed to express phenotype - dominant and capital letter



recessive ✔️if two copies are needed, the allele is said to be recessive and is usually represented witha
lowercase letter



homozygous ✔️if both alleles are same for given gene, individual is said to have a homozygous
genotype



heterozygous ✔️if alleles are different, individual has a heterozygous genotype

,hemizygous ✔️genotype that describes a situation in which only one allele is present for a given gene,
such as X chromosome in males



complete dominance ✔️when only one dominant and one recessive allele exist for a given gene. In this
case, presence of one dominant allele will mask recessive allele if present.



codominance ✔️when more than one dominant allele exists for a given gene, there codominance. I.e.,
a person with one allele for the A blood antigen and one allele for B blood antigen will express both
antigens simultaneously



incomplete dominance ✔️when a heterozygote expresses a phenotype that is intermediate between
the two homozygous genotypes. I.e. mating of certain flowers in which a red flower crossed with a white
flower --> pink flowers



interplay of genes with environment ✔️penetrance and expressivity



penetrance ✔️population measure defined as the proportion of individuals in the population carrying
the allele who actually express the phenotype. In other words, it is the probability that, given a
particular genotype, a person will express the phenotype.



full penetrance ✔️The allele is said to have complete penetrance if all individuals who have the
disease-causing mutation have clinical symptoms of the disease.



I.e.Individuals with over 40 sequence repeats in Huntington's have a full penetrance - 100 percent of
individuals with this allele show symptoms



high penetrance ✔️most, but not all of those with allele show symptoms of disease.



Individuals with fewer sequence repeats show high penetrance in Huntington's

, reduced penetrance ✔️penetrance is said to be reduced when some individuals fail to express the trait,
even though they carry the allele.



low penetrance ✔️in allele with low penetrance will only sometimes produce the symptom or trait with
which it has been associated at a detectable level. In cases of low penetrance, it is difficult to distinguish
environmental from genetic factors.



nonpenetrance ✔️The state in which a genetic trait although present in the appropriate genotype fails
to manifest itself in the phenotype.



expressivity ✔️varying phenotypes despite identical genotypes.



Expressivity can be constant or variable



constant expressivity ✔️if expressivity is constant, then all individuals with a given genotype express
the same phenotype



variable expressivity ✔️if expressivity is variable, then individuals with the same genotype may have
different phenotyps



expressivity vs penetrance ✔️penetrance: is a population parameter (what percent of indivdiuals with a
given genotype express the phenotype)



expressivity: explores grey area in expressoin and is more commonly considered at the individual level.



Mendel's 1st law ✔️Law of segregation



4 tenets

1. Genes exist in alternative forms (alleles)

2. An organism has two alleles for each gene, one inherited from each parent

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