chapter 3 - heredity, cell biology and evolution

Cells

The building blocks of life that makes up all living things and is where all metabolic processes associated with life occurs

Cell history

All cells come from pre existing cells through division

• they carry hereditary material that gets passed onto new cells after division

4 main components of eukaryotic cells and what they are

Cell membrane - holds goop inside

Organelles - carry’s out cells vital functions

Cytosol - the goop

Nucleus - stores DNA

6 types of cells

1. Nerve

2. Muscle

3. Bone

4. Gland

5. Blood

6. Reproductive

DNa strcuture

• Double helix molecule of two chains that form a ladder

• Nucleotides link the chain

• 4 bases (ATCG) are used to write the genetic code

3 components of nucleotide

1. Deoxyribose sugar

2. Phosphate salt

3. Nitrogenous base

Gene

List of amino acid required to build a specific protein made of a chain of amino acids formed by codons

How do organisms grow and reproduce

Cells have a complete copy of its genetic code and uses it to divide then replicate itself

• they use base pairings to exactly copy without creating mistakes

2 instances of DNA replication

1. Growth and repair (mitosis)

• DNA replicates everytime a cell divides to help grow multicellular organisims

2. Reproduction (meiosis)

• sex cells have half as many chromosomes and pass it onto their offspring

Chromosome

Coiled up DNA molecule

How many chromosomes do humans have

46 chromosomes, one from each parent in pairs

Crossing over

Homologus chromosomes exchange portions with each other to reduce genetic linkage and make sure every daughter cell is unique

• occurs in prophase 1

Differences of mitosis and meiosis

Mitosis

• one division

• 2 identical daughter cells

• 46 chromosomes (diploid)

• Produces somatic cells

Meiosis

• 2 divisions

• 4 unique daughter cells

• 23 chromosomes (haploid)

• Produces sex cells

Mendals pea plants

Conducted hybrid experiments to study inheritance

• noticed that plants produced discrete traits with no blending

What did we learn from mendals pea plants

• Traits are controlled by genes with 2 different alleles

• The expressed allele in dominant, the hidden is recessive

• Genes occur in pairs, one from each parents and are found in homologus pairs

Genotype phenotype

G - genetic makeup

P - physical appearance determined by genotype

Gene locus

Location for a specific gene on a chromosome

Homozygous and heterozygous

Homo - 2 of same allele

Hetero - one dom one rec

Punnet square

Used to predict the possible genotype and phenotype of offspring if both genotype of parents are known

Principle of segregation

When individuals reproduce, alleles segregate and one gets passed to the offspring at random

• because this occurs for both parents, chromosome pairs are restored in fertilization

Principle of independent assortment

Genes controlling different traits are inherited independently from one another since the genes are on different chromosomes

Sex linked traits

Independently assort due to recombination

Codomiance

Both alleles are dominant and both are expressed at the same time

Ex. Camellia sinensis and strawberry roan horse

Incomplete dominance

Neither allele s dominant and the phenotype is a blend of the two

Ex. Snapdragons

Medialian trait

A trait controlled by one gene at a single locus

Polygenic traits

More than one gene contributes to a trait

Pleiotropy

One gene contributes to several different traits

What type of trait is blood type

It’s a Mendelian trait

• A and B are codomiant

• O is recessive

Polygenic inheritance

More than one gene contributes to their expression

• the expression of these traits are continuous and not discrete

What trait is skin colour

Polygenic

• determined by melanin (pigment), either brown or red, produced by melanocytes

• Many genes control melanin production and they have an additive effect

Which blood type is most frequent and what does it show

O is most popular despite being recessive. Recessive does not equal less frequent

Epigenetics

Study of traits that change due to environmental effects, not just genetically

Which genes interact with environment during growth and development

Regulatory genes

3 key difference of birds from dinosaurs

1. Beaks

2. Wings

3. Short tail

Mitochondrial inheritance

Mitochondria has unique DNA called mtDNA, inherited from their mothers. Variations in this dna caused by mutations help with studying genetic change over time

Building a modern theory of evolution

Combined Darwins idea that natural selection acted on variation in populations and Mendals idea about how variation was inherited

2 stage process of Modern synthesis of evolutionary theory

1. Production and redistribution of variation

2. Selective forces acting on variation of different individuals will affect their ability to reproduce successfully

Current definition of evolution

A change in allele frequency from one gen to the next

• its nonrandom reproduction producing directional change in allele frequencies to specific environmental factors

Allele frequency

Indicators of genetic makeup of a population where members share a common gene pool. They refer to the percentage of all the alleles at a locus accounted for by one specific allele

4 forces of evolution

1. Mutation

2. Gene flow

3. Genetic drift

4. Natural selection and other selective factors

Mutations

Copying mistake in the genetic code and is the only way to create new genes

• mistakes in mitosis could hurt the individual like cancer

• Mistakes in meiosis can lead to evolution

How can mutation be good, neutral or bad

Good - new gene works better

Neutral - non coding DNA is affected or the new codon codes for the same amino acid so no change

Bad - gene is broken and affects health of individual

How does sexual reproduction and recombination increase variation

Shuffles genes around

Recombination

• changes gene location on chromosomes (shuffling of genes)

• Recombination decreases genetic linkage to increase variability

• Affects how some genes act and function to which natural selection can act upon

• DOESNT CHANGE ALLELE FREQ

Gene flow

Exchange of genes between populations caused by migration or not

Gene flow through migration and without migration

Migration - individuals move from one population to another and introduce their genes to the gene pool through interbreeding

Without - two separated populations may interact at their boundary passing genes between pools

Genetic drift

Random changes between generations as a result of sampling error

• in small populations through random chance the alleles that are passed on may not reflect the frequencies of those in the previous generation

Bottle neck effect

A type of genetic drift where a drastic change in population size due to a random event that decreases diversity to which the smaller population may not reflect the original population

Founders effect

Type of genetic drift where a new population starts with a small isolated group from a larger one resulting in reduced divsersity and different allele frequencies than the original

Other types of selective forces

1. Artificial breeding - selectively breeding livestock and crops where humans are the selective pressure

2. Sexual selection - non random mating due to preference of opposite sex, where selected traits may not be adaptive in an environmental context even if potential partners are attracted to it