LOtopic 3 a - b

Question 1

Describe the main components of DNA and how DNA is arranged on a chromosome; define the term ‘gene’

Answer 1

Gene is genetic code kept in chromosome (24)
Double strand of twisted helix

Question 2

Define cell differentiation, and list the three categories of cells in multicellular organisms (stem cells, other cells capable of dividing, and permanently differentiated cells).

Answer 2

Eukaryotic cell division results in 2 daughter cells
Differentiation when the daughter cell become specialised for specific functions
Stem cells - self renewal, it continues to divide into more cells
Permanently differentiated cells - cannot divide, only change
Other capable of dividing - embryos, juveniles and adults can divide

Question 3

Describe sexual and asexual reproduction, and list which types of organisms use which mode of reproduction

Answer 3

sexual - offspring are the result of a fusion of gametes, go through meitioc division and have of each parents gene are inherited
asexual - offspring produced from one parent, bacteria, some multicellular organisms and clones.

Question 4

Describe the phases of the cell cycle in prokaryotes and the process of binary fission

Answer 4

The DNA replicates and the two chromosomes split on their respective side of the cell attaching to the membrane.
Plasma membrane grows and pushes between the dna, splitting cell until there are two cells

Question 5

Define the following terms related to chromosomes: chromatid, centromere, telomere, kinetochore

Answer 5

Chromatid - one of the identical chromosomes produced during cell division
Centromere - place where chromatids attach to the kinetochore and daughter double helix after cellular respiration.
Telomere - end of the chromosome (sequence)
Kinetochore - where microtubules attach to move the s=chrmosomes during division.

Question 6

Describe the cell cycle in eukaryotes; identify the phases of mitosis and describe what occurs in each one

Answer 6

Interphase - has three phases G1- girth and differentiation, s - synthesis of DNA and duplication of chromosomes, G2 cell growth and preparation for division.
Prophase - dna an separated by chromosome not aligned
Metaphase - chromosome aligned and spindles attached
Ana phase - membrane begins to separate the two chromosomes
Telophase/cytokinesis - separated by a action ring/ cell plate

Question 7

Describe how the processes of mitosis and cytokinesis differ between animal and plant cells

Answer 7

Plants have a cell plate and animals have a action ring with a cleavage furrow

Question 8

Describe how the cell cycle is controlled and the checkpoints that regulate it

Answer 8

Growth receptors (enzymes) trigger division
Main checkpoints are G1 to S (Cell intact and good to go?), G2 to mitosis (Is DNA replicated right) and metaphase to anaphase (are chromosomes attached to the spindle /aligned right?

Question 9

Describe the advantages of sexual reproduction, and the role of mutations in contributing to genetic variation

Answer 9

Sexual reproduction allows for a genetic variation from two individuals which increases chances for mutation which in turns boost genetic variation.

Question 10

define alleles, locus/loci, karyotype, homologous chromosomes, alleles, autosomes, sex chromosomes, haploid, diploid, polyploid

Answer 10

Alleles - one or mores genetic sequences at a locus
locus/loci - location of the genome
Karyotype - appearance of the total set of chromosomes
Homologous - pair of the same genes2
Chromosomes - a sequence of amino acids holding genetic information
Autosomes - the non sex chromosomes
Sex chromosomes - sex determination chromosomes (X and Y)
Haploid - cell with one set of chromosomes
Diploid - cell with two sets of chromosomes
Polypoid - when a diploid acquires more chromosomes

Question 11

Define and use correctly the terms, locus, allele, genotype, phenotype, dominant, recessive, homozygous, heterozygous

Answer 11

Locus - the area where specific genes are kept
Allele - genes found at the same locus
Genotype - codes of genes
Phenotype - physical manifestation of genes
Dominant - variant of traits that overpower recessive trait
Recessive - weaker traits that get overpowered
Homozygous - pair of homologous chromosomes with the same gene form
Heterozygous - pair of homologous chromosomes which carry different alleles

Question 12

Explain how sexual reproduction & meiosis contributes to variation in offspring, including crossing over.

Answer 12

During meiosis the exchange of genetic material occurs during prophase 1 otherwise known as ‘crossing over’
As well as during independent assortment in metaphase 1 of meiosis does chromosomes get randomly selected to create gametes.

Question 13

Explain the phases of meiosis and how this process results in the formation of a haploid cell

Answer 13

Meiosis consists of two phases each time the chromosomes are split into two cells resulting in four haploid cells.
Interphase, prophase, metaphase, anaphase, telophase, all occur in both phases of meiosis.

Question 14

Compare and contrast the processes of mitosis and meiosis

Answer 14

Meiosis has two phases as it produces four haploid cells while mitosis only has one phase to produce two diploid cells
They both have interphase, prophase, metaphase, anaphase, telophase.

Question 15

Discuss the foundations for our understanding of genetics and explain how Mendel’s experiments contributed to our understanding of inheritance of a single gene

Answer 15

Foundations - offspring from differing genes of plants are hybrids the offspring are known as first filial generation (F1) their offspring are the in thee (F2) generation.
Mendel - Using true breeding plants allowed him to view the full effects of genetic information on hybrids. The inheritance of dominant and recessive alleles on homologous chromosomes explains the results of Mendel’s crosses

Question 16

Define the term ‘test cross’ and explain its use

Answer 16

Used to deduce if the dominant phenotype is heterozygous or not.
Used to predict the outcome of new types of single trait crosses

Question 17

State the basic concepts of segregation and independent assortment, as identified in Mendel’s Principles

Answer 17

Segregation - The pairs of alleles on homologous chromosomes separate, or segregate, from each other during meiosis
Independent assortment - The independent inheritance of two or more traits. Multiple traits are inherited independently because the alleles of one gene are distributed to gametes independently of the alleles for other genes. Independent assortment will occur when the traits being studied are controlled by genes on different pairs of homologous chromosomes

Question 18

Describe what is meant by incomplete dominance, codominance, polygenic inheritance and pleiotropy

Answer 18

Incomplete dominance - the characteristics (phenotype) of a heterozygous individual is s mix (intermediate) of each parent being homozygous.
Codominance - when two alternative alleles are expressed (phenotype) simultaneously
Polygenic inheritance - when one characteristic is controlled by two or more genes (hight, skin colour, eye colour, and weight
Pleiotropy - a single gene controls more than one phenotypic trait

Question 19

List examples of traits that are influenced by interaction between genes and the environment

Answer 19

Traits affected by polygenic inheritance are often strongly affected by the environment, further blurring the differences among phenotypes
Human skin colour is influenced by exposure to sunlight
Human height is influenced by nutrition

Question 20

Explain the physical arrangement of genes on chromosomes and the difference between autosomes and sex chromosomes; define sex-linked traits

Answer 20

Genes are arranged on chromosomes which are in identical pairs except the x and y chromosomes, they are shaped differently than the autosomes
Chromosomes - a sequence of amino acids holding genetic information
Autosomes - the non sex chromosomes
Sex linked traits - traits that are on the X or Y chromosomes