week 21 Flashcards by Molly McCaig

what are the stages of mitosis

Prophase, Prometaphase, Metaphase, Anaphase and Telophase

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what are somatic cells

any body cells that do not produce gametes (egg/sperm)

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what are germ cells

a diploid reproductive cell that gives rise to a gamete

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whats the difference between diploid and haploid

diploid= 2 sets of chromosomes
haploid= 1set of chromosomes

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what is the locus

the particular location on a particular chromosome where genes are located

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what are histones

proteins, which help with the folding and structural support of chromosomes. DNA is wrapped around histones

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how does methylation affect DNA

affects how tightly coiled the DNA is and switches genes off

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how many chromosomes do humans have

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what are autosomes

the 22 pairs of chromosomes that do not determine sex

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what is the human karyotype

an ordered display of the pairs of chromosomes in a cell

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what is epigenetics

the study of the chemical modification of specific genes or gene-associated proteins of an organism

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when does meiosis begin

after S phase in cell cycle

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what happens in meiosis I

homologous chromosomes separate. 2 haploid daughter cells are formed- reductional division.

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what happens in meiosis II

sister chromatids separate. 4 haploid daughter cells are formed. each with a haploid set of unreplicated chromosomes.

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whats the difference between mitosis and meiosis in terms of chromosome sets

mitosis conserves number of chromosome sets while meiosis reduces the number of chromosome sets (from diploid to haploid).

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whats unique about meiosis

at the metaphase plate there are paired homologous chromosomes (tetrads) instead of individual replicated chromosomes. homologous chromosomes separate instead of sister chromatids. synapsis and crossing over- homologous chromosomes physically connect and exchange genetic info.

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what is the chiasma

the crossover point on homologous chromosomes which join to form an X shape

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what is genetics the study of

heredity and variation

are identical twins the same

monozygotic (identical) twins are genetically identical and morphologically similar

what is a mutation

spontaneous changes in genetic information

what are the sources of variation

sexual reproduction and mutations

what is anagenesis

micro evolution, describing gradual change within a single lineage over time

what is cladogenesis

macro evolution, describes the branching of evolutionary lineages where an ancestor can give rise to two or more descent species.

what is a lineage

a sequence of species, each of which is considered to have evolved from its predecessor

what is autopolyploidy

polyploidy within a single species, where multiple copies of the same genome are present

what is allopolyploidy

polyploidy resulting from the combination of chromosomes from different species, often from hybridisation

define polyploidy

a condition where and organism or a cell has more than two complete sets of chromosomes

define allopatry/ allopatric speciation

Species divergence happens due to geographically isolated areas. the same event can affect many lineages at once

define sympatry/ sympatric speciation

Speciation occurs in the same area, genetic isolation without a geographical barrier. caused by sexual selection.

what is genetic isolation

when populations diverge to the point where they can no longer interbreed

define geogra[hic differentiation

different forms of the same species in different geographical areas

what are the types of selection

directional- when one extreme phenotype is favoured diversifying/ disruptive- two extreme phenotypes are favoured, while the average is less succesful stabilising- when the average phenotype is favoured

what is the S phase of the cell cycle

the period where the cell replicates its DNA

when does mitosis occur

before cytokinesis, after G2 in the cell cycle

what is the composition of chromosomes in diploid cells

46 chromosomes in total; 23 from each parent

what is meiosis

cell division producing gametes each possessing the haploid number of chromosomes and haploid content of DNA. allows reproduction where offspring have half genetic info from each parent

how many daughter cells are produced by meiosis

4 haploid daughter cells.

what are tetrads

two pairs of homologous chromosomes, resulting in 4 chromatids in meiosis

what is independent assortment of chromosomes

each homologous pair can line up independently during metaphase I, producing genetic variation

how does the chiasmata crossing over point produce variation

sister chromatids break and rejoin

what does natural selection result in

accumulation of genetic variations favoured by the environment

what is a cross between two parents that differ at a single gene called

a one factor cross

what are reciprocal crosses used to determine

whether a trait is sex-linked (led to the X or Y) or autosomal (non-sex chromosome)

what is hemizygosity

when an individual has only one copy of a gene where two are expected