3B INHERITANCE AND CELL DIVISION

define a stem cell

a cell that has not differentiated and so has the ability to become a number of different types of cell

examples of specialized cells in animals

ciliated cell (moves mucus in bronchus and trachea)

nerve cell (axons covered in fatty sheath that insulates and speeds up nerve transmission

red blood cell (transports O2 efficiently due to bioconcave shape, contains haemoglobin and no nucleus)

examples of specialised cells in plants

root hair cell (absorbs water and mineral ions, increased SA and thin walls)

palisade mesophyll cell (performs photosynthesis, tightly packed, column shaped, contains chloroplasts)

advantages of using stem cells in medicine

• greater potential to treat a wide variety of diseases from diabetes and paralysis

• organs developed form a patient’s own stem cells reduces the risk of rejection and wait time

• adult stem cells are already used successfully in many cases, proving its benefits.

disadvantages of using stem cells in medicine

• stem cells cultured in labs could become infected with a virus, transmitting it to the patient

• cultured stem cells could accumulate mutations leading them to develop cancer cells

• low numbers of stem cell doners

what is a genome

a genome is the entire DNA of an organism

what is a gene

a gene is a section of DNA found on a chromosome that codes for a specific protein, function or characteristic

what is the nucleus

the nucleus is where chromosomes are located

what is the structure of DNA

DNA is a polymer made made up of two strands coiled around and held together by hydrogen bonds to make a double helix

what are the four bases in DNA

• Adenine

• Thymine

• Guanine

• Cytosine

what is the differences in structure of RNA v.s. DNA

RNA is single-stranded and contains Uracil instead of Thymine.

what happens during protein synthesis?

• protein synthesis turns a gene into a specific protein

• transcription - DNA is transcribed and mRNA molecule is produced

• translation - mRNA is translated and a protein is produced

what are triplet bases called on mRNA

codon

what are triplet bases on tRNA called

anticodon

what happens during transcription

• The DNA unzips when hydrogen bonds between base pairs break

• This exposes the template strand of the gene

• Free complementary mRNA bases line up on the template strand

• This forms a single strand of mRNA, which leaves the nucleus

what happens during translation

• After leaving the nucleus, the mRNA molecule attaches to a ribosome

• The anticodon on each tRNA molecule pairs with a complementary codon, bringing its specific amino acid with it

• A peptide bond is formed between the two neighboring amino acids

• Once a ‘stop’ codon is reached, the amino acid chain if folded and modified to form the final protein (e.g. enzyme, antibody)

what is an allele

an allele is a different form of a gene (e.g. brown eye allele and blue eye allele). allele’s of the same gene produce a different protein, leading to a different phenotype

what is a genotype

a genotype is the combination of alleles

what does homozygous/heterozygous mean

homozygous - two of the same alleles (BB or bb)
heterozygous - two different alleles (Bb)

what is a dominant allele

a dominant allele is always expressed in the phenotype if present in the genotype

what is a recessive allele

a recessive allele is only expressed in the phenotype is paired with anothe recessive allele

what is codominance

sometimes both alleles within a genotype are expressed in the phenotype of an individual. (e.g. A + B = AB)

what is a polygenic trait

a polygenic train is a trait that is controlled by more than one gene. most traits are polygenic.

What are the female and male genotype?

females - XX

males - XY (father controls the gender of the baby)

what is a diploid cell

a diploid cell is a cel that contains two complete sets of chromosomes

what is a haploid cell

a haploid cell is a cell that contains one complete set of chromosomes

how many chromosomes do human diploid cells have

human diploid cells have 46 chromosomes, so haploid cells therefore have 23

what is mitosis

mitosis is nuclear division giving rise to genetically identical cells

when does mitosis occur

• growth

• repair

• cloning

• asexual reproduction

how does mitosis happen

• each chromosome in the nucleus copies itself exactly (x shaped chromosomes)

• chromosomes line up along the centre of the cell, cell fibers pull them apart

• the cell divides into two, each new cell has a copy of each of the chromosomes

what is meiosis

meiosis is a type of nuclear division that gives rise to cells that are genetically different

how does meiosis happen

• chromosomes double themselves (x formed), and line up in the centre of the cell.

• the cells divide twice - first the chromosomes pairs divide, then each chromosome divides

• this gives four haploid daughter cells (gametes) which are genetically different

how does meiosis create genetic variation?

• each gamete produced in meiosis carries substantially different alleles

• during fertilization, any male gamete can fuse with any female gamete to form a zygote

• this random fusion of gametes creates genetic variation between zygotes

what are some examples of genetic variation in humans

• blood group

• eye colour

• gender

• ability to roll tongue

what is a species

a species is a group of organisms that can reproduce to form fertile offspring