Lecture 2

Question 1

Hereditary similarity and variation

Answer 1

• offspring resemble parents more than less closely related individuals of same species
• transmission of traits from generations is hereditary inheritance

Question 2

inheriting chromosomes

Answer 2

• 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)

Question 3

sexual/asexual reproduction

Answer 3

• 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

Question 4

human cells contain sets of chromosomes

Answer 4

• 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)

Question 5

Meiosis

Answer 5

• cells fuse (syngamy)

Question 6

sexual life cycles

Answer 6

• 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

Question 7

meiosis

Answer 7

• replication of chromosomes
• Meiosis 1 (separates homologous chromosomes)
• meiosis 2 (separates sister chromatids)

Question 8

interphase

Answer 8

• chromosomes replicated to form sister chromatids
• genetically identical
• joined by centromere
• single centrosome replicated (two centromeres)

Question 9

prophase 1

Answer 9

• 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

Question 10

Metaphase 1

Answer 10

• tetrads arranged at metaphase plate (chromo. facing each pole)
• microtubules from poles attached to kinechore of one chromo. of each tetrad

Question 11

anaphase 1

Answer 11

• homologous chromo. separate (to each pole)
• siter chromatids remain attached at centromere

Question 12

telophase 1 and cytokinesis

Answer 12

• haploid set at each pole
• cytokinesis occurs same as mitosis (cleavage furrow / cell plate)
• no chromosome replication occurs

Question 13

prophase 2

Answer 13

• spindle forms at kinetochores
• spindles at each pole

Question 14

metaphase 2

Answer 14

• 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)

Question 15

Anaphase 2

Answer 15

• centromeres separate, two new individual chromosomes towards poles

Question 16

telophase 2

Answer 16

• nuclei form around chromosomes
• expanding
• cytokinesis separates cytoplasm
• result in four haploid daughter cells

Question 17

key differences

Answer 17

• diploid vs. haploid
• identical daughter to parent vs. genetically distinct

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Question 18

genetic variation

Answer 18

• behaviour of chromo. during meiosis and fertilisation result in most variation
• independent assortment
• crossing over
• random fertilisation

Question 19

independent assortment

Answer 19

• random orientation of homologous pairs of chromo. at (M) phase 1
• 50/50 chance for particular daughter cell of meiosis to get maternal chromo. ; same for paternal
• homo. pair of chromo. segregate independently of homo. pairs during (M) phase 1
• ## 1st meiotic division = independent assortment of maternal/paternalchromo.

Question 20

crossing over

Answer 20

• recombinant chromo. combine inherited genes from parents
• crossing early (P) phase 1 as homo. chromo. pair up gene by gene
• portions of two nonsister chromatids trade
• for some organisms essential for synapsis and proper assortment
• combining DNA inherited from two parents in single chromo.
• (M) phase 2; nonidentical chromatids sort independently from one another (increase no. of genetic types formed by meiosis)

Question 21

Random nature of fertilisation

Answer 21

• arising from meiosis
• any sper/egg fusion
• more than 70 trillion possibly comb. of chromo. for zygote (unique identity)

Question 22

evolutionary adaptation

Answer 22

• Darwin (genetic variation in evolution)
• evolve through differential reproductive success of its variant members (best suited to live in particular environment have most offspring)
• natural selection = adaptations
• environment change = new genetic comb. that work best (formerly favoured genes will decrease)
• sex + mutation continually new genetic variability
• Mendel