biology Exam 3

The stages of mitosis

arrange a cells chromosomes spatially so they can be duplicated and divide

5 phases of mitosis

prophase, prometaphase, metaphase, anaphase, telophase

cytokinesis

cleavage of the cell into equal halves

Mitosis makes cells that..

are genetically identical to each other

Overview of Meiosis

meiosis is a form of nuclear division that leads to the production of gametes (in animals).

Gametes

egg and sperm cells

Gametes are

haploid

Adult body cells (somatic cells)

are diploid, containing 2 sets of chromosomes

Sexual Reproduction

includes the fusion of gametes (fertilization) to produce diploid zygote.

sexual reproduction & meiosis =

genetic diversity

Prophase 1

Difference in mitosis:

-homologous become closely associated in Synapsis

-Crossing over

Crossing Over

genetic recombination between non-sister chromatids

Metaphase 1

- microtubules from opposite poles attach to each homologue

- homologues are aligned at the metaphase plate side-by-side

- the orientation of each pair of homologous on the spindle is random

Each gene arrangement results in..

a different gamete

Meiosis II resembles a

mitotic division

Prophase II (Meiosis)

nuclear envelope dissolves and spindles apparatus form

Metaphase II (Meiosis)

chromosomes align on metaphase plate

Anaphase II (Meiosis)

sister chromatids separated from each other

Telophase II (Meiosis)

nuclear envelope re-forms; cytokinesis follow

no crossing over in

meiosis

Trait

particular form of a character (ex.: red flowers)

Recessive

masked in phenotype when heterozygous

Character

observable physical feature (ex. floral color)

Dominant

fully expressed in phenotype

Gene

units of inheritance, segment of DNA that codes for a protein

Allele

Different forms of a gene

Phenotype

physical expression of the organism (ex: red or white flower)

Genotype

The composition of alleles of an organism

genetics

study of heredity and variation

Heredity

continuity of biological traits from one generation to the next

Variation

difference among individuals of the same species (due to environment and genetic components.

dominant allele

fully expressed in phenotype; masks recessive allele; ex. S= Spherical

recessive allele

masked in phenotype when heterozygous (genotype); ex. s= wrinkled

Types of genotypes

homozygous, heterozygous

Homozygous

having two identical alleles for a given character

SS= homozygous dominant for smooth seeds

ss= homozygous recessive for wrinkled seeds

Heterozygous

having two different alleles for a trait

-Ss

heredity

inheritance from parents to offspring

Variation

differences among offspring

F1 generation

First filial generation - offspring produced by crossing 2 true breeding strains

F2 generation

offspring results from the self-fertilization of F1 plants

the terms ratio, frequency, percent, and proportion

are all parts of a whole

Mendel's Law of Segregation

during gamete formation, alleles separate so that each gamete receives only one allele for each gene.

monohybrid cross

cross between two individuals regarding only one gene locus of interest; only have 2 variations

Mendel's Law of Independent Assortment

Alleles governing different traits assort independently of each other during meiosis

-your genotype for one character does not determine a second character

-came from work with dihybrid crosses

dihybrid cross

a cross between two individuals that differ in two traits

(ex. RrYy)

In meiosis

MANY gametes are made in individuals

-

MANY gametes are released into the environment, with all possible genotypes from an individual.

-

ONE egg will be fertilized by one sperm

mitosis, meiosis, and mendelian genetics are

at an individual level

population genetics

the study of genetic variation and its causes within population

Darwin

Evolution is descent with modification

Evolution

Genetic changes through time.

1. species accumulate difference

2. descendants differ from their ancestors

3. new species arise from existing ones

natural selection

Proposed by darwin's as the first mechanism of change.

1. individual have inherited characteristics

2. they produce more surviving offspring

3. the population includes more individuals with these specific characteristics

4. population evolves and is better adapted to its present environment

Gene variation in nature

measure levels of genetic variation at different loci

Locus

the place on a chromosome where a gene is located

Single nucleotide polymorphism (SNP)

single base change in DNA used to look at many loci at once.

-happens from mutation (error)

Darwin's Theory of Natural Selection

Different survival & reproduction; genetically-based variation leads to evolutionary change

-variation results of pre-existing differences

Genetic Variation

we can use genetic markers to identify groups of genetically similar humans

Hardy-Weinberg Principle

The original proportions of the genotypes in a population will remain constant from generation to generation as long as 5 assumptions are met.

Gene Pool

sum of all alleles in a population

genetic variation within populations

-An allele's frequency = number of copies of allele in pop/sum of all alleles in the population

-allele frequencies range from 0 to 1

-Sum of all allele frequencies at a locus = 1

Allele Frequencies equation

p+q = 1

p= frequency of dominant allele

q= frequency of recessive allele

Genotype frequencies equation

p² + 2pq + q² = 1

The Anthropocene

We are in it right now.

-marked by human activity

-climate change in the atmosphere

-change identified in sediments

(stratigraphic signature)

Hardy-Weinberg assumptions

1. No Mutation takes place

2. No genes are transferred to or from another sources (no movement)

3. Random mating is occuring

4. The population size in very large

5. No selection occurs (no change)

Forces of Evolution

1. mutation

2. gene flow (migration)

3. non-random mating

4. genetic drift

5. selection (change)

Mutation

A change in a cell's DNA.

- mutation rates are generally so low they have little effect on hardy-weinberg proportions of common alleles

- ultimate source of genetic variation

Gene Flow

A movement of alleles from one population to another.

-powerful agent of change

-tends to homogenize allele frequencies

Non-Random Mating

mating with specific genotypes.

-shifts genotype frequencies

-assortative mating- "likes mates with like"

Genetic Drift

Random fluctuations in allele frequencies over time.

-important in small populations

founder effect (genetic drift)

few individuals found new population

bottleneck effect (genetic drift)

drastic reduction in population, and gene pool size

What causes extinction of species?

H- habitat loss/destruction

I- Invasive species

P- pollution

P- Human Population

O- Over-harvesting; Poaching

Natural Selection

environmental conditions determine which individuals in a population produce the most offspring.

3 conditions for natural selection to occur:

1. variation must exist among individuals in a population

2. variation must be genetically inherited

3. variation among individuals must result in differences in the number of offspring surviving

Fitness

genetic contribution of a genotype to the next generation relative to other genotypes.

Fitness is a combination of:

1. survival: how long does an organism live

2. mating success: how often it mates

3. number of offspring per mating that survive

How is fitness measured?

one way is via mean # surviving offspring in the next generation

3 kinds of natural selection

stabilizing selection,

directional selection,

disruptive selection

stabilizing selection

Selection may favor average individuals for a phenotypic character = stabilizing selection

-mean stays the same, tails pull in

(ex. human birth weight)

directional selection

Selection may favor individuals at one extreme for phenotypic character = directional selection

-mean shifts toward one direction

(ex. cliff swallows after bad weather - surviving birds were larger than dead birds)

disruptive selection

Selection may favor individuals at both extremes = disruptive selection

- mean stays the same but shape of curve changes

-rarest form of selection

stabilizing selection dia.

directional selection dia.

disruptive selection dia.