3 Inheritance Flashcards
What is mitosis?
Diploid cell copies itself and divides into two identical diploid daughter cells.
The daughter cells are clones of each other.
Every base pair of their DNA is identical
How many pairs of chromosomes are in a diploid human body cell?
23 pairs
46 chromosomes
How does a cell undergo mitosis?
cell grows
DNA replicates to form two copies of each chromosome. Copies are joined together at a single point
Chromosomes line up across centre of cell, attached to special spindle fibres
The chromatids (copies) are pulled apart and move to opposite ends of cell
The cytoplasm and cell membrane divides to form two identical cells
What is mitosis used for?
growth, repair and asexual reproduction
What is meiosis?
cell devision that produces four genetically different haploid cells
chromosome number is halved
How does a cell undergo meiosis?
parent cell grows
DNA replicates to form two copies of each chromosome
The homologous pairs of chromosomes join together and exchange sections of DNA
Then attach to spindle fibres in pairs at centre
Homologous pairs are pulled apart and move to opposite ends of the cell
Chromosomes line at centre of cell, attached to spindle fibres, chromatids separate and move to opposite ends of cell
Each cell divides again
Mitosis produces…
genetically identical daughter cells
Meioisis produces…
haploid gametes (sperm, eggs, pollen) which aren’t genetically identical
only used to produce gametes for sexual reproduction
How many chromosomes does a human haploid cell have?
23 chromosomes (unpaired)
What are the differences between meiosis and mitosis?
Mitosis:
2 genetically identical daughter cell produced
Involves one cell division
Produces diploid cells in humans
Keeps same chromosome number
Meiosis:
4 genetically non-identical daughter cells
Involves two cell divisions
Produces haploid cells in humans
Halves number of chromosomes
What are the differences in the roles of Mitosis and Meiosis?
Mitosis:
generates all adult cells except gametes (growth and repair)
occurs throughout human body
occurs throughout a plant
used for asexual reproduction
Meiosis:
only used to produce gametes
only occurs in ovary and testis
only occurs in ovary and anther
used for sexual reproduction
What is fertilisation?
when haploid sperm and egg gametes fuse - will have full number of chromosomes
How does random fertilisation produce genetic variation in offspring?
it’s random which sperm/ pollen grain fertilises an egg - therefore variation in offspring
genetic variation in gamete cells produced by meiosis (sperm cell and egg cell)
random fertilisation of ova (egg cells) by male gametes
What is a gene?
a section of a molecule of DNA which does for a specific protein
provides information on sequence of amino acids in a protein (e.g. an enzyme) which then control chemical reactions, growth, colouration and all inheritable characteristics
Gene codes for a characteristic
What is a genome?
One copy of all an organism’s DNA
(the entire DNA of an organism)
In humans this is all the DNA that makes up the 23 pairs of chromosomes found in all diploid body cells (all cells except sex cells or gametes, which only have half a person’s genome)
Where is there a pair of genes for each characteristic?
in every diploid nucleus
nucleus contains chromosomes on which genes are located
PAPER 2 Describe a DNA molecule
double helix shape (two strands wrapping around each other)
PAPER 2 What is a nucleotide?
consist of a sugar (deoxyribose), a phosphate and a nitrogenous base
PAPER 2 What are the 4 types of nitrogenous base?
Adenine - Thymine
Guanine - Cytosine
PAPER 2 What are nucleotides joined together by?
covalent bonds between the sugar of one nucleotide and the phosphate group of the next nucleotide
FORMS: sugar phosphate backbone
PAPER 2 Describe an RNA molecule
ribonucleic acid
RNA nucleotides are joined to form a single strand
PAPER 2 What is the sugar in RNA called?
ribose
PAPER 2 What is the base in an RNA strand?
Uracil - Adenine
PAPER 2 What are the two types of RNA?
mRNA - messenger RNA.
Formed in nucleus of cell
tRNA - transfer RNA.
Found in cytoplasm
PAPER 2 What is transcription?
mRNA copies the sequence of bases of a section of DNA:
Two strands of DNA helix are unzipped - caused by enzyme helicase
The enzyme RNA polymerase attaches to DNA just before gene
RNA polymerase moves along the DNA strand
RNA polymerase catalyses the formation of covalent bonds between RNA nucleotides to form a strand of mRNA
strand of mRNA is opposite copy of DNA strand (except U replaces T) - called complementary copy
mRNA leaves nucleus to go to ribosome
PAPER 2 What is translation?
for every 3 mRNA bases (codon) the ribosome lines up one complementary molecule of tRNA (complementary 3 bases of tRNA called anticodon)
tRNA picks up specific amino acids from cytoplasm and transports to ribosome
ribosome allows two tRNA molecules to sit next to each other
ribosome catalyses the formation of a peptide bond between 2 amino acids
chain of several hundred amino acids forms in specific order polypeptide folded into correct shape and becomes a specific protein