Inheritance Flashcards
Where are chromosomes found?
In the nucleus of a cell
What are chromosomes?
Thread-like structures that carry genetic info, each carry large number of genes
What do different genes control?
Development of different characterises
What do each body cells have? (chromosome wise)
2 copies of each chromosome (1 from mother and 1 from father)
How many chromosomes do human cells have?
46
What is the cell cycle?
Series of stages where cells divide to produce new cells
What is the name of the stage of the cell cycle when a cell divides?
Mitosis
What is mitosis used for?
To grow or replace cells that are damaged
What do you get at the end of a cell cycle?
2 new cells identical to original cell (with same number of chromosomes)
Where does mitosis occur?
In normal body cells
What does mitosis result in? (mention chromosomes)
Results in 2 diploid cells produced + with 2n chromosomes in daughter cell
Explain how mitosis works
- Copies of genetic material are made
- The cell then divides once to form two genetically identical body cells
How can you represent normal body cells?
2n
How can you represent gametes?
n
What can you call normal body cells?
Diploid
What can you call gametes?
Haploid
What is an allele?
Different version of a same gene
Humans have ___ versions of every gene
2 (1 from dad and 1 from mum)
What can alleles be?
Recessive or dominant
How do you represent a dominant allele?
With a capital letter e.g. A
How do you represent a recessive allele?
Lower case letter - a
What is a genotype?
Combination of alleles
What is a phenotype?
Characteristic
What does Aa represent?
Heterozygous
What does AA represent?
Homozygous Dominant
What does aa represent?
Homozygous Recessive
What is sexual reproduction?
Involves the fusion of male and female gametes. Because there are TWO parents, the offspring contain a mixture of their parents’ genes.
What is asexual reproduction?
When there’s one parent. No fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. Offspring are genetically identical to parent - clones.
Why is there variation in offspring for sexual reproduction?
- Egg and sperm fuse together (fertilisation) to form cell with full number of chromosomes 2. Mixture of genetic info produces variation in offspring
In humans, how many chromosomes do each gamete contain?
23 chromosomes (half number of chromosomes in normal cell)
How asexual reproduction happen?
By mitosis
Give an example of a plant that reproduces asexually?
E.g. strawberry plants produce ‘runners’
What are chromosomes essentially (i.e. what are they made out of)?
Long molecules of DNA
What is DNA (composition wise)?
A polymer
What is DNA made up of?
2 strands coiled together in shape of double helix
What is DNA?
- A chemical that all genetic material in a cell is made up from
- Contains coded information that determines inherited characteristics
Describe how genes produce proteins (4 marks)
- Gene = sequence of bases
- 3 bases code for 1 amino acid
- Order of bases controls order of amino acids
- Amino acids are assembled to make (specific) protein
What is a gene?
Small section of DNA found on a chromosome
How many amino acids are used to make proteins?
20
What do the strands in DNA contain?
Four different compounds called bases
_ ___ code for 1 amino acid
3 bases
How many types of DNA bases are there?
4
What does the order in amino acids control?
The order in which amino acids are assembled to produce a particular protein
Name 3 examples of types of proteins
- Hormones
- Enzymes
- Structural Proteins (e.g. collagen - very strong)
Not all genes are switched __
on
What switches on certain genes?
Stem cells
What do cells in reproductive organs divide to form?
Gametes
How are gametes produced?
By Meiosis
How many cells are produced in meiosis? (mention no. of chromosomes)
4 cells (with n number of chromosomes in daughter cells)
Explain how meiosis works
- Copies of genetic information are made
- Cells then divides twice to form 4 gametes, each with a single set of chromosomes
How does an (human) organism form (after fertilisation)?
- After 2 gametes fuse, new cell divides by mitosis to make copy of itself
- Mitosis repeats many times = produce lots of new cells in embryo
- As it develops, cells differentiate & become specialised to make up whole organism
What is variation?
Differences within a specie
What causes variation?
- Genes
- Environment
What causes genetic variation?
Combining of genes (from mum and dad)
What are most characteristics due to?
Genes AND the Environment
Give an example of genetic and environmental characteristic and explain it
Height:
- Maximum height of animal is determined by genes
- Whether it grows that tall depends on its environment
What else introduces variation?
Mutations
What are mutations?
Changes to sequence of bases in DNA
What pair of chromosomes determine your sex?
23rd pair
In females, are sex chromosomes the same or different?
Same (XX)
In males, are sex chromosomes the same or different?
Different (XY)
What is meant by homozygous?
Both chromosomes in a pair contain the same allele of a gene
What is meant by heterozygous?
Chromsomes in a pair contain different alleles of a gene
What is meant by recessive?
Not expressed if dominant allele present
What 3 conclusions did Mendel reach?
- Characteristics in plants = determined by “hereditary units”
- Hereditary units = passed onto offspring unchanged from both parents, unit from each
- Hereditary units can be recessive or dominant - if individual has both, dominant will be expressed
Give 3 examples of genetic disorders
- Polydactyly
- Cystic Fibrosis
- Sickle Cell Anaemia
What does polydactyly cause?
Organism to have extra fingers/toes
What allele causes polydactyly?
Dominant allele
What are symptoms of cystic fibrosis?
Lots of mucus in air passages and pancreas = Problems with breathing, digestion and infertility
Cystic fibrosis is a genetic disorder of…
cell membranes
What allele causes cystic fibrosis?
Recessive allele
What does sickle cell anaemia cause?
Causes red blood cells to become ‘sickled’ in shape = can’t carry oxygen as well + cells can become damaged
What allele sickle cell anaemia is carried on?
Co-dominant allele
Sickle cell anaemia in carried on a co-dominant allele, what does this mean for their red blood cells?
Some will be sickled and some will be normal
How is Down’s syndrome caused?
By the presence of an extra chromosome
How can embryos can be screened for genetic disorders?
- During IVF, embryos are fertilised in lab
- DNA isolated from embryo
- Probe mixed with embryo DNA
- Probe binds with embryo DNA
- Show alleles/genes for disorder +ive = discarded OR -ive = implanted into uterus
Name 3 reasons for embryo screening
- Treating disorders costs government (& taxpayers) lot of money
- Stop people suffering
- Laws to stop it from going too far
Name 3 reasons against embryo screening
- Increase prejudice: implies people with genetic problems are ‘undesirable’
- Screening is expensive
- May come a point where people want to screen embryos so they can pick most ‘desirable’ one
What is selective breeding?
When humans artificially select plants or animals that they’re going to breed
Why is selective breeding done?
So genes for desired characteristic remain in population e.g. Crops with disease resistance
Describe the process of selective breeding
- From existing stock, select ones with desired characteristics
- Breed them with each other
- Select best of offspring & breed them together
- Continue process over several generations - desirable trait gets stronger and stronger
- Eventually, all offspring will have characteristic
Name the drawback of selective breeding
Reduces gene pool i.e. no. of different alleles in population decreases (DUE to inbreeding)
Why does inbreeding causes health problems?
More chance of organisms inheriting harmful genetic deflects when gene pool is limited
If new disease appears, how might it affect an inbreed population and why?
Reduced gene pool = less chance of resistant alleles present in population = little variation ∴ most of population may die (all stock are closely related)
What is genetic engineering?
Transferring desired gene to other organism so it has desired characteristics
Describe the process of genetic engineering
- Useful gene is isolated (cut) from organism’s cell using enzymes into vector (usually virus or bacterial plasmid)
- Vector is introduced to target organism, useful gene is inserted into its cell(s)
How can we make organisms develop with desired characteristics?
Transfer of gene is carried out when organism receiving gene is at early stage of development (e.g. egg/embryo)
Name 4 uses of genetic engineering
- GM crops
- Treat diabetes
- Gene therapy
- Treating human diseases
Explain how genetic engineering can be used to treat diabetes
Bacteria - genetically modified to produce human insulin
Explain how genetic engineering can be used to treat human diseases - use an example
Sheep - genetically engineered to produce substances, like drugs, in their milk
What is gene therapy?
Researching genetic modification treatments for inherited diseases (e.g. by inserting working genes)
Describe how bacteria can be engineered to produce human insulin
- Remove insulting gene out of a human cell using a special enzyme
- Remove plasmid from a bacterial cell
- Break plasmid open using special enzyme
- Add insulin gene into plasmid, using a different specialised enzyme
- Allow genetically modified plasmid to be taken up by a bacterial cell
- Bacteria multiply serval times
- Insulting gene is “switched on” and bacteria begin to produce insulin
- Culture bacteria and process insulin
Name 2 pros of GM crops
- Increases crop yields
- Some crops can be modified to provide more nutritional value
How can using GM crops increase crop yields
- GM crops can be produced to be resistant pests (insects and herbicides) 2. Can be genetically modified to grow better in drought conditions
Name 3 cons of GM crops
- Don’t fully understand effects of eating them on human health
- Reduces farmland biodiversity
- Transplanted genes may get into natural environment
How might GM crops reduces farmland biodiversity?
GM crops will affect number of wild flowers (and population of insects)
What is bad thing about GM crops transplanting genes into the natural environment?
E.g. herbicides resistance gene may be picked up by weeds - ‘superweed’
Name 2 ways plants can be cloned
Via:
- Tissue Culture
- Cuttings
Describe cutting
- Small piece of plant removed - stem of leaf
- Stem treated with rooting hormones
- Replanted in soil, with moist, warm conditions perfect for growth
Explain how tissue culture works
Few plant cells put in growth medium with hormones and grow into new plants = clones of parent plant
What are advantages of taking a cutting? (name 3)
- Simple (older method used by gardeners)
- Plants produced quickly and cheaply
What are advantages of using a tissue culture? (name 3)
Plants can be made:
- very quickly
- in very little space
- & grown all year
Who uses tissue cultures? (name 2 groups)
- Scientists to preserve rare plants that are hard to reproduce naturally
- Plant nurseries to produce lots of stock quickly
Explain how animals can be cloned using embryo transplants
- Sperm cells taken from prize male and egg cells taken from prize female
- Sperm used to artificially fertilise egg cell to produce embryo
- Embryo is divided into number of individual cells
- Each cell divides into a identical embryo
- Cloned embryos implanted into uterus of host mothers and identical offspring are born
Describe how adult cell cloning works
- Haploid nucleus is removed from unfertilised egg cell (enucleated)
- Diploid nucleus is removed from adult body cell (e.g. skin cell) and inserted into ‘empty’ egg cell
- Egg cell is stimulated by electric shock - makes it divide like normal embryo
- When embryo is ball of cells, it’s implanted into womb of adult female
- Grows into genetically identical copy (clone) of original adult body cell - has same genetic info
Name 3 pros of cloning
- Study of animal clones = lead to greater understanding of…
- Development of embryo
- Ageing and age-related disorders
- Help preserve endangered species
- Gets lots of ideal offspring
Name 3 cons of cloning
- ‘Reduced gene pool’ - fewer alleles in population
- Worry - humans may be cloned in future
- Cloned animals may not be as healthy as normal ones
What is the disadvantage of a ‘reduced gene pool’?
If population is closely related and new disease comes = could be wiped out
Bc no allele in population giving resistance
What is the issue with cloning humans?
Any success may follow many unsuccessful attempts e.g. there may be children born severely disabled
Every cell has ____ genes and chromosomes but…
Every cell has SAME genes and chromosomes but NOT ALL are switched on
How are GM crops made?
Infect plant embryos with bacteria = so genes get incorporated into plant genes
