B13 Reproduction

DNA - found in nucleus that controls protein synthesis

Proteins synthesised in ribosomes

DNA - made up of sugar and phosphate 

Each sugar has a base attached to it. Bases = A C G and T

Sugar + Phosphate + Base= Nucleotide

Three bases on DNA code for one amino acids. Amino acids make up proteins

Order of bases controls how amino acids make a particular protein

DNA Molecule - C to G and A to T in opposite strands. Protein synthesis controlled by DNA

1. Template made by genes in DNA

2. Template leaves the nucleus

3. Template attaches to ribosome

4. Carrier molecules attached to specific amino acids become attached to template in specific order given by DNA

5. Amino acids joined together to make protein

6. Protein molecule folds to form a unique shape for its function e.g enzymes, hormones or forming structure in body like collagen.

Change in order of bases changes template which makes different amino acids and therefore protein changes as well.

Gene codes for protein = gene expressed

Non-coding DNA switches genes on and off - variation in this area can affect gene expression (phenotype)

Mutation - changes in existing genes. Mistakes in copying DNA

Mutations in coding DNA - almost no alteration when the protein formed

Some mutations code for change in amino acids ---> altered protein---> different shape ---> substrate may not fit enzyme/weaker structural protein

Mutations are good - more efficient enzyme or stronger structural protein

Some characteristics controlled by a single gene - red-green colour blindness in humans and fur colour in mice

Allele - different form of gene

The alleles (genotype) present, operate at a molecular level to express characteristics (phenotype)

Homozygous - two identical alleles e.g. BB or bb

Heterozygous - two different alleles e.g. Bb

Genotype - the alleles present e.g. Bb or bb

Phenotype - the physical characteristic e.g. black fur

Dominant - allele that is always expressed, only if one copy present

Recessive - allele that is expressed, only if both copies are present

Sex of a child is determined by the sex chromosomes

Human females - **

Human males - XY

Pregnancy = 50:50 chance of having a boy or girl

Polydactyly - extra fingers or toes. Caused by dominant allele.

Cystic fibrosis - mucus buildup affects organs, especially lungs and reproductive system (infertility)

No cure for CF

Caused by recessive allele. Both parents must be carriers for someone to have CF so (Cc). 

Offspring

25% will be non-carriers and not have the disorder (CC genotype)

50% will be carriers but not have the disorder (Cc genotype)

25% will have CF (cc genotype)

Screening embryos. Amniocentesis - fluid taken from developing fetus containing fetal cells 

Chrionic villus - sample of tissue from placenta containing fetal cells

Risk of miscarriage in both, invasive

IVF embryos tested before implantation, so only babies without disorder born.

Concerns 

Processes used for screening can cause miscarriage.Healthy fetus may be miscarried (distressing).

False positive or false negative results - termination of healthy child or child with disorder born. 

Religious beliefs and emotions. 

Costs

Asexual reproduction 

One parent

Cells divide by mitosis

No fusion of gametes so no mixing of genetic information = no variation in offspring

Offspring are genetically identical to parent (clone)

Sexual reproduction

Fusion of gametes from male and female forming zygote. Gametes produced by meiosis

Offspring inherit mix of genetic information = variation

Plants gametes = egg cells and pollen

Human gametes = egg cells and sperm cells

Meiosis - cell division process by which gametes are made in humans. Female egg cells produced in ovaries and male sperm cells produced in testes.

1. Cell with 46 chromosomes (2n diploid) 

2. Each chromosome duplicates itself. Duplicate is called a chromatid. Cell with 92 chromosomes.

3. Similar chromosomes come together and cross genetic information. Cell with 92 chromosomes.

4. Cell divides in two. 2 cells produced each contain 46 chromosomes (2n diploid)

5. 2 cells divide into 2 again. 4 gametes produced with 23 chromosomes each. Each gamete contains a random mixture of genetic information, different to others.

6. Gametes join at fertilisation to restore normal number of chromosomes (46) = new cell

Variation present in sexual reproducation because of mixing of genetic info

Advantages of asexual reproduction

• only one parent needed
• time and energy efficient (no need to find a mate)
• faster than sexual reproduction
• many identical offspring can be produced in favourable conditions

Advantages of sexual reproduction

• produces variation in the offspring
• if the environment changes, variation gives a survival chance by natural selection
• natural selection can be sped up by humans in selective breeding to increase food production.

Malarial parasites - asexually in human host, seuxally in mosquito

Fungi - reproduce asexually by spores, reproduce sexually to give variation

Plants (runners) - like strawberries produce asexually as well as sexually 

Cell--->Nucleus--->Chromosomes--->DNA--->Genes--->Amino acids--->Proteins

DNA = polymer of 2 strands, double helix, contained in chromosomes

Gene = section of DNA. Codes for sequence of amino acid to make protein

Genome = entire genetic material of an organism

Importance of human genome

• search for genes linked to different types of disease (predicting risk, choosing cancer treatment suited to individual)
• understanding inherited disorders (overcoming them through meds, repairing faulty genes)
• use in tracing human migration patterns