Evo. Chapter 6: Transmission Genetics and Variation

who was deemed the father of modern genetics?

gregory mendel

what did gregory mendel used to study genetics?

pea plants

what did mendel test?

whether traits were inherited as discrete units or became blended

what is a true breeding organism?

one that produces an offspring like itself; now known as a homozygote

mendel discovered that each parent plant had to copies of…?

genes; what he referred to as factors

how do two gene copies separate?

they separate with equal probability into gametes

what is mendel’s first law?

the law of segregation

what does the law of segregation state?

that each individual has two copies of a gene at each locus and that these gene copies segregate during gamete production so that only one gene copy goes into the gamete

what is a locus?

the physical location of gene copies on a chromosome

who discovered dominant and recessive alleles?

mendel

what is mendel’s second law?

the law of independent assortment

what does the law of independent assortment state?

an allele passed down to the next generation at one locus is independent of an allele passed down at another locus

does mendel’s second law hold true for both linked and unlinked genes?

no; only true for unlinked

how will mendel’s second law act on linked traits?

it won’t; effects on one trait will affect the other

why was mendel’s discovery of particulate inheritance important as related to darwin’s theory?

because it helped to explain how sufficient variation could be maintained within a population

do genes blend?

no; they can mix to form intermediate forms, but because they are particulate they can revert to an unmixed phenotype; EX: blue and yellow filters can make green, but will always be inherently blue and yellow

what does DNA stand for?

deoxyribonucleic acid

what is the chemical basis for all life on earth?

DNA

how do changes in DNA relate to changes in fitness?

small changes in DNA can have large effects on fitness

what is used to reconstruct phylogenetic relationships?

changes in DNA across populations/species

what is a polymer?

a macromolecule composed of repeating units linked together in a chain

what are the four nucleotides?

adenine, thymine, cytosine, guanine

what three components form a nucleotide?

1. pentose sugar (deoxyribose)

2. phosphate group (phosphate and four oxygen)

3. nitrogenous base

what are the purines?

nitrogenous bases that contain five and six sided rings; adenine and guanine

what are the pyrimidines?

nitrogenous bases that contain six sided rings only; cytosine, thymine

what connects nucleotides in a double-stranded DNA molecule?

hydrogen bonds

name the two ends of a DNA molecule and what is found at each end

5’: terminal phosphate group

3’: terminal hydroxyl group

how is a DNA molecule oriented?

two complimentary strands are antiparallel; nitrogenous bases are at interior

what are the DNA nucleotide pairings?

A to T and G to C

where is DNA located in the cell?

in the chromosomes

what are diploid organisms?

organisms that have two copies of each chromosome

what are haploid organisms?

organisms that have a single copy of each chromosome

what protein does DNA wrap around?

histones

how many pairs of chromosomes do humans have?

23

how many chromosomes do chimps have (humans closest living relative)?

24

name some characteristics of eukaryotic cells

1. contain nucleus

2. contain membrane-bound organelles

which two organelles have their own genomes?

1. mitochondria

2. chloroplast

name some characteristics of prokaryotic cells

1. no nucleus

2. no membrane-bound organelles

3. singular circular chromosome reminiscent of that found in mitochondria and chloroplasts

4. contain plasmids

5. DNA not wrapped around histones

what is a plasmid?

an accessory DNA structure found in prokaryotes; replicate independently of the cell’s chromosome

what does the endosymbiosis hypothesis state?

organelles such as mitochondria and chloroplasts were once independent prokaryotes that entered into a mutually beneficial relationship with a eukaryote and over time, were incorporated into these cells and became organelles

who proposed the endosymbiosis hypothesis?

lynn margulis

why did the mutually beneficial relationship form?

the bacteria gave energy to the eukaryote and the eukaryote provided protection to the bacteria

what does it mean for a relationship to be obligate?

the two parties involved become dependent on one another

what is transcription?

the process by which DNA is unwound and copied into RNA

what protein facilitates transcription?

RNA polymerase

where does RNA polymerase bind?

to the promoter region

what is the promoter region?

a short sequence before the transcribed part of a gene of interest

how is DNA unwound?

breaking of hydrogen bonds between nucleotides

which strand is synthesized to form an RNA strand?

the template strand

what nucleotide replaces thymine in RNA?

uracil

for natural selection to act, the genes must affect the genotype or phenotype?

phenotype

which way is the RNA strand transcribed?

in the 5’—>3’ direction

what is translation?

the protein synthesis process

what molecule directs translation?

mRNA

what are codons?

base pair sequences in sets of three that specify for a specific amino acid

how many codons are there?

64; 61 code for amino acids, 3 are stop codons

what are the three other types of RNA?

1. ribosomal RNA

2. tRNA

3. microRNA

what is ribosomal RNA?

a major component of ribosomes

what role do ribosomes have in translation?

function in protein production by making the covalent bonds that link the amino acids together

what is tRNA?

RNA that transports amino acids to the ribosomes

what is microRNA?

RNA involved in gene regulation

what are proteins?

strains of amino acids that are the essential building blocks of life

how many amino acids are there?

20

what is the genetic code?

the culmination of all codons and which amino acid they code for

what does it mean when we say the genetic code is redundant?

one amino acid can be coded for by multiple codons, especially if there is a mutation in the third codon position

what are five roles of proteins?

1. enzymes that regulate chemical reactions

2. chemical signals for cell communication

3. binding DNA to regulate it

4. structural

5. transport

what is a gene?

a sequence of DNA that specifies a functional product (usually a protein but may also be RNAs)

what are the two regions of a eukaryotic gene?

1. exons

2. introns

what are exons?

stretches of DNA that code for protein products

what are introns?

stretches of DNA that do no normally code for proteins; spliced out by spliceosome

what is alternative splicing? why is it important?

the process of splicing one RNA transcript in multiple ways; allows for one gene to code for multiple proteins

what are alleles?

variants of the same gene

what is a genotype?

a combination of alleles that an individual has at a given locus or at all loci

what is a homozygote?

a diploid species that has two copies of the same allele at a locus

what is a heterozygote?

a diploid species that has different alleles at a locus

how can you determine whether and allele is dominant or recessive?

dominant: a heterozygote is phenotypically identical to one of the differing homozygous parents, then that trait is dominant

recessive: the other allele in question would be recessive

what is incomplete dominance/codominance?

when both alleles show in the phenotype; EX: red and white flower making pink

what is a punnet square?

a diagram used to predict the results of a genetic cross

what are regulatory elements?

molecules that act in transcriptional regulation, and therefore influences gene expression

what are enhancers?

regulatory elements that increase the rate of transcription

what are silencers?

regulatory elements that decrease transcription

what are cis regulatory elements?

regulatory elements that affect genes at nearby sites on the same chromosome

what are trans regulatory elements?

regulatory elements that modify expression or activity of genes on different chromosomes

how do trans regulatory elements work?

the use soluble proteins that can act on remote locations on the DNA

what is epigenetic inheritance?

heritable mechanisms that alter gene expression without making changes in the DNA sequence

how may epigenetic changes be inherited?

from cell to cell and/or parent to offspring

what is a chromosome made of?

chromatin

what is chromatin?

DNA wrapped around histone proteins

how does the orientation of chromatin affect gene expression?

condensed chromatin: DNA cannot be accessed for transcription

decondensed: DNA is accessible for transcription

what are the two secondary modifications involved in epigenetics?

1. DNA methylation

2. acylation of histone proteins

describe how DNA methylation affects gene expression

adding a methyl group to a CG base pair; if highly methylated, then inaccessible to RNA polymerase

describe how histone acylation affects gene expression

causes chromatin to decondense, allowing for transcription

what is developmental plasticity?

adjustment of a phenotype in response to environmental factors early on in life; EX: a mother’s diet during pregnancy can influence the child’s change of developing type II diabetes later in life

how is epigenetics likely inherited?

through small RNA molecules

what allows cell types to differ?

differences in gene expression that are often driven by epigenetics

what is X chromosome inactivation?

the inactivation of one X chromosome in anXX female via methylation of histone proteins; ensures proper expression of genes on X chromosome

what is genomic imprinting?

differentiated gene expression due to methylation that is dependent on wether the gene is inherited from the mother or the father

what are the four sources of genetic variation?

1. recombination

2. mutation

3. migration

4. lateral gene transfer

where do the pairs in a homologous chromosome come from?

each comes from one parent

what is a gamete?

a haploid sec cell with one set of chromosomes; EX: eggs, sperm