B13 Genetics and Reproduction Flashcards
What is Asexual Reproduction?
- Only involves one parent
- Cells divide by mitosis
- no joining of gametes (sex cells), no mixing genetic information, NO VARIATION IN OFFSPRING= genetically identical offspring (clones)
- common in small animals + plants, fungi, bacteria
- body cells-> growth, replace worn out tissue
What is Sexual Reproduction?
- male sex cell and female sex cell (gametes/parents cells fuse) fuse to form zygote-> forms genetically varying offspring
- gametes form through meiosis
- inherit genetic information from both parents
- more variation in offspring than asexual reproduction
Plants gametes= egg cells, pollen
Animals= egg cells (ova), sperm
Why is Sexual Reproduction risky and good?
- relies on 2 sex cells, often from 2 individuals, meeting and fusing
- BUT introduces variation= key to long term survival of a species
Where does Meiosis take place?
In the reproductive organs of animals and plants
- humans= ovaries and testes
What is the process of Meiosis?
only takes place in reproductive organs
- all chromosomes in the cell are copied
- the genetic material moves to the edges of the cell and divides into two
- the genetic material moves to the edges of the cell again
- the cell divides one more time (forming 4 genetically varying gametes-> half the number of chromosomes in a normal cell)
How many chromosomes are there in a cell?
23 pairs
1 from mother= maternal chromosomes
1 from father= paternal chromosomes
What is a Haploid?
a cell that only has half the amount of normal genetic material
ie gametes (23 single chromosomes)
What happens in Fertilisation?
- 2 sex cells join, forming a single new cell with a full set of chromosomes
- unique cell, begins dividing rapidly by mitosis
- cells differentiate as embryo develops (tissues, organs, organ systems)
What is the difference between Asexual and Sexual reproduction?
Asexual
- offspring produces from mitosis of parent cells
- same chromosomes, same genes
- no variation in genetic material
Sexual
- gametes produces by meiosis in sex organs of parents
- variation: each gamete is different
- gametes fuse, more variation
What are the advantages and disadvantages of Asexual Reproduction?
- only 1 parent, less time and energy wasted finding a mate/spreading gametes
- faster than sexual reproduction
- environmental changes can cause species to die out (lack of variation, cannot adapt
What are the advantages and disadvantages of Sexual Reproduction?
- produces varying offspring, survival advantage if environment changes (natural selection)
- 2 parents/ gametes are needed-> time and energy to find mate/spread gametes
How does Fungi usually reproduce?
Asexual
- toadstool, puffballs= asexual fruiting bodies full of spores
- mould= reproduce asexually
Why and how do Fungi reproduce sexually?
- when conditions aren’t good ie dry
- 2 hyphae from different fungi join, nuclei fuse, hypha has 2 sets of chromosomes
- meiosis, haploid spores, may produce fungi better adapted to changing conditions
How do plants reproduce?
Sexually- pollen and egg cells (gametes)
- pollen reaches egg cell of another plant= pollination (Insects, birds)
- pollen fuses with egg cells, seeds are formed
- variation, plants survive in changing conditions (natural selection)
How can some plants reproduce asexually?
specially directed mitosis
- tiny new plants form on runner stems (strawberry plants, spider plants)
neg= new plants are identical to parents, no variation
pos= new plants formed even if flowers are destroyed (frost, eaten etc)
How do the parasites that cause malaria reproduce?
Both Asexually and Sexually
Asexually= in human host
Sexually= in mosquitos
the mosquito takes blood meal, temp drops between human body, mosquito triggers Sexual reproduction in parasites in red blood cells
- sexual forms develop, burst out of blood cells, meet + form zygotes
- zygotes undergo meiosis, produce new asexual parasites, infect new human host
What does DNA stand for?
Deoxyribonucleic acid
What is DNA?
A polymer made up of many repeating units
What are chromosomes made of?
Long molecules of DNA
- in long strands of DNA twist and spiral, form double helix structure
What are genes?
small sections of DNA where genetic information (determining inherited characteristics) is stored
- each gene codes for a specific sequence of amino acids-> make specific protein
- genes control proteins, proteins control make up of specialised cells that form tissues, tissues form organs, organs systems make up whole body
What is the genome of an organism?
The entire genetic material of an organism
What is the Human Genome Project?
a project that sequences the entire human genome
How does the Human Genome code for so many proteins?
it uses the same gene in different ways or switches part of a gene on and off
Why is sequencing genomes
important?
- importance in medicine
- work out relationships between different types of organisms
- can identify causes of disease, help choose right treatment
Why is understanding the human genome important?
- understand inherited disorders (cystic fibrosis)
- understand genes linked to specific types of diseases (type 2 diabetes, cancer)
- track human migration, evolution
Where is DNA found?
In the nucleus of cells
What is a nucleotide?
the combination of a sugar, phosphate and base
What are the 4 letters of bases?
AT
CG
What is a DNA polymer made up of?
repeating nucleotide units
How many bases code for 1 amino acid?
3
How many bases are in a gene?
hundreds or thousands
What does the order of bases control?
Which amino acids are assembled to produce a specific protein in the body cells
What does a gene code for?
- a particular combination of amino acids, making up a specific protein
Why are complementary strands (AT, CG) in DNA important
- Holds the double helix structure together
- Important for information from genes on the DNA to be translated into proteins in the cells
What is the process of Protein synthesis?
- genes produce template for protein, reflecting sequence of bases in the DNA + small enough to leave nucleus through nuclear membrane
- leaves nucleus + binds to ribosome
- cytoplasm contains carrier molecules each attached to specific amino acid
- carrier molecules attach to template in order given by DNA
- amino acids join to form specific protein
- protein detaches from carrier molecules, molecules detach from template + return to cytoplasm to pick up more amino acids
What are uses for proteins produced from protein synthesis?
Enzyme- fold to produce an active site
Structural protein- form fibrous structures like collagen
Hormone/Muscle/Part of cell membrane structure- fold to carry out specific job in cell
When is a gene expressed?
When a gene codes for a protein that is synthesised in the cell
What are uses for non-coding parts of the DNA?
Switching genes/parts of genes on and off
- variation in non coding parts can affect how genes are expressed -> affects phenotype
What is a Phenotype?
The physical appearance of biochemistry of an organism
What are mutations?
new forms of genes resulting from changes in existing genes
- often occur in mistakes made in copying DNA
What are effects of mutations on proteins made?
- most don’t alter protein formed, but can alter appearance but not function
- can code for change in amino acids, cause altered protein that folds to give a different shape-> active site may no longer fit substance OR structural protein loses strength
- can give advantage (eg produce more efficient enzyme OR stronger structural protein)
How can mutations in Non-coding DNA affect the phenotype?
- doesn’t directly affect the phenotype
HOWEVER
- variants in non coding DNA: affects which genes are switched on and off, changing genes expressed-> effect phenotype
What is an allele?
A variant/different form of gene that each code for a different protein
- combination of alleles inherited determines characteristics
(genes= chromosomes that carry genetic information)
What is a Homozygote?
an individual with 2 identical alleles for a characteristic
BB, bb
What is a Heterozygote?
An individual with different alleles for a characteristic
Bb
What is a Genotype?
The genetic makeup of an individual regarding a particular characteristic
Bb, bb etc
What is a Phenotype?
The physical appearance of an individual regarding a particular characteristic
Black fur or Brown fur in mice
What is the difference between a Dominant allele and a Recessive allele?
Dominant= always expressed in the phenotype, even if only 1 copy is present
Recessive= only expressed if 2 copies are present
What are sex chromosomes?
1 pair of chromosomes out of 23 that differ, determining the sex of offspring
Female (human)= XX
Male (human)= XY
What are inherited disorders?
disorders result of change in bases or coding of our genes, passed from parent to child
What is Polydactyly?
babies born with extra fingers/toes
- usually caused by dominant allele
- if it is a heterozygous gene, there is a 50% chance of passing it to children
- if it is a homozygous gene, there is a 100% chance of passing it to children
What is Cystic Fibrosis?
Genetic disorder, affecting lungs, digestive system and reproductive system. Treatment includes physiotherapy, antibiotics to keep lungs clear of mucus + infection, no cure
- caused by recessive phenotype
- has to be inherited from both parents
What is a carrier?
When a parent carries a recessive unhealthy allele but have a dominant healthy allele, so have no symptoms but can pass the disease to their children
How can people screen for genetic disorders?
- use genetic tests to show people if they are a carrier of a faulty gene
- screen pregnancies (embryos and fetuses) for alleles that cause inherited disorders
- embryos can be screened before implantation during IVF
- useful tests, raise ethical concerns
How can you screen embryos?
- harvest cells from developing individual
Amniocentesis:
- 15-16 weeks of pregnancy
- taking amniotic fluid from around fetus. Contains fetal cells, used for genetic screening
Chorionic villus sampling:
- 10-12 weeks of pregnancy
- taking small sample of tissue from placenta, provides fetal cells to screen
What are the disadvantages of screening embryos?
- associated risk of miscarriage, distressing for parents
- can give false pos/neg results-> termination of healthy baby, unexpected birth of child with genetic disorder
- leaves decision of terminating baby (hard decision)
- expensive process
- could give rise in demand to ‘designer babies’-> parents used screening to choose children with desirable characteristics (looks, sex, intelligence)
What happens if screening shows an embryo is affected by genetic disorders?
Parents can choose between keeping the baby with a genetic disorder or have an abortion/not proceed with implantation (IVF)
