Lecture 2 Flashcards
1
Q
Hereditary similarity and variation
A
- offspring resemble parents more than less closely related individuals of same species
- transmission of traits from generations is hereditary inheritance
2
Q
inheriting chromosomes
A
- genes programme specific traits that emerge from fertilised eggs to adults
- genes are segments of DNA transmitted as specific sequences of four doexyribonucleotides (analogous to symbolic info. of language in which words and sentences translated to mental image; cells translate genetic ‘sentences’ into frekcles and other features with no resemblance to genes)
- most genes program synthesis of specifc enzymes and other proteins whose action produces inherited traits
- transmission of hereditary traits has molecular basis in precise replication of DNA (produces copies of genes passed from parents to offspring)
- genes from sperm and egg present after fertilisation
- each chromosome single DNA molecule with various proteins
- each gene at a specific location (locus)
3
Q
sexual/asexual reproduction
A
- asexual = exact copies
- single organism (mitotic division; budding, producing a mass of cells by mitosis)
- two parents produce offspring (unique combination of genes inherited)
- vary genetically
4
Q
human cells contain sets of chromosomes
A
- somatic = 46 chromosomes (distinguished by size, position of centromere, pattern of staining with certain dyes)
- arranged into pairs by size (karyotype)
- homologous chromosome pairs carry genes control inherited characters
- 22 pair autosomes, 1pair sex chromosome (small parts of X, Y homologous; most of X have no counterparts in Y vice-versa)
5
Q
Meiosis
A
- cells fuse (syngamy)
6
Q
sexual life cycles
A
- fertilisation, meiosis alternate ; timing does vary among species
- animals
- fuse to form diploid zygote, divide by mitosis
- plants
- alternation of generations
- two multicellular stages (haploid; diploid)
- saprophyte = diploid; haploid = spores by meiosis that develop by mitosis into gametophyte
- fungi, some protists
- gemetes fuse form zygote
- meiosis to form haploid
- haploid grow by mitosis form haploid multicelluar adult
- gametes produced by mitosis
7
Q
meiosis
A
- replication of chromosomes
- Meiosis 1 (separates homologous chromosomes)
- meiosis 2 (separates sister chromatids)
8
Q
interphase
A
- chromosomes replicated to form sister chromatids
- genetically identical
- joined by centromere
- single centrosome replicated (two centromeres)
9
Q
prophase 1
A
- chromosomes condense
- homologous chromo. loosely pair
- crossing over (DNA nonsister chromatids break at corresponding places then rejoin other)
- in synapsis proein structure (synaptonemal complex) forms between corresponding homologous
- dissassembles late prophase (each chromosome pair become visible tetrad)
- terad has 1+ chiasmata (sites where homo. chroma. have crossed and segments of chroma. have been traded)
- spindle form
- breakdown of nuclear envelope and nucleoli
- kinetochores of each homo. attach to microtubules from poles
10
Q
Metaphase 1
A
- tetrads arranged at metaphase plate (chromo. facing each pole)
- microtubules from poles attached to kinechore of one chromo. of each tetrad
11
Q
anaphase 1
A
- homologous chromo. separate (to each pole)
- siter chromatids remain attached at centromere
12
Q
telophase 1 and cytokinesis
A
- haploid set at each pole
- cytokinesis occurs same as mitosis (cleavage furrow / cell plate)
- no chromosome replication occurs
13
Q
prophase 2
A
- spindle forms at kinetochores
- spindles at each pole
14
Q
metaphase 2
A
- because crossing in meiosis 1; two sister chromatids of each chromo. no longer genetically identical
- kinetochorse of sister chromatids attach at microtubules (extending opposite poles)
15
Q
Anaphase 2
A
- centromeres separate, two new individual chromosomes towards poles
