Inheritance - gcse bio

What does DNA stand for?

deoxyribonucleic acid

What is DNA?

The chemical that all of the genetic material in a cell is made up from

what does dna contain?

Coded information - all the instructions to put an organism together and make it work

What does your DNA determine?

What inherited characteristics you have and proteins you code

What is DNA made up of?

Two strands coiled together in the shape of a double helix

what does a gene do?

codes for a specific protein

what is a gene?

segment of DNA that codes for a protein

what does each gene code for?

A particular sequence of amino acids which are put together to make a specific protein

How many amino acids are used?

20, but they make up thousands of different proteins

what is a genome?

The entire set of genetic material in an organism

Why is understanding the human genome important

- allows scientists to identify genes linked to different types of diseases
- knowing genes linked to inherited diseases could help develop effective treatments
- genomes can trace the migration of certain populations.

what are dna strands?

Polymers made up of lots of repeating units called nucleotides

What does each nucleotide consist of?

One sugar molecule, one phosphate molecule and one 'base'

what are the complementary base pairings?

A, T, C, G

A and T always pair up. what is the pairing called?

complementary base pairings

what does the order of bases in a gene decide?

the order of amino acids in a protein

What do non-coding parts of DNA do?

Switch genes on and off to control gene expression

What does mRNA do?

messenger, contains the information from DNA to make protein by translation

where are proteins made?

ribosomes in the cytoplasm

what are the function of enzymes

act as biological catalysts to speed up chemical reactions in the body

what is the role of hormones?

used to carry messages around the body

what do structural proteins do?

physically strong

what are mutations

change to the genetic code

how do mutations occur

mutations occur spontaneously but can be made to occur more often due to exposure to certain substances or some types or radiation

how do mutations work?

they change sequences of the DNA bases in a gene which produces a genetic variant. as the sequence of DNA bases code for the sequence of amino acids that make up a protein, mutations in protein sometimes lead to changes in protein that it codes for

how do mutations affect a protein?

most have very little to no effect on the protein. some will change it to such a small extent its function or appearance is unaffected. however some mutations will seriously affect a protein

how could a mutation affect a proteins ability to form it's function?

- if the shape of an enzymes active site is changed its substrate may no longer be able to bind to it
- structural proteins like collagen could lose their strength if their shape is changed, making them useless for providing structure and support

if there's a mutations in the non-coding dna what can happen?

it can alter how genes are expressed

What are insertions?

Insertions are where a new base is inserted into the Dna base sequence where it shouldn't be

What are the different types of gene mutation?

insertions
deletions
substitutions

Explain how an insertion affects DNA?

an insertion changes the way groups of three bases in a DNA base sequence codes for a particular amino acids

how can insertions continue?

by creating a knock on effect

what are deletions?

deletions are when a random base is deleted from a base sequence. they can cause a knock on effect

what are substitutions?

substitution mutations are when a random base in the DNA base sequence is changed to a different base

what does sexual reproduction?

sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically different to either parent

in sexual reproduction what do the mother and father produce

gametes by meiosis

in humans what does each gamete contain?

23 chromosomes - half the number of chromosomes in a normal cell

what happens to the parent cells during sexual reproduction

they fuse together to form a cell with the full number of chromosomes

why does the offspring inherit features from both parents

it's received a mixture of chromosomes

how is genetic in offspring produced

the mixture of genetic information

what does asexual reproduction produce

genetically identical cells

in asexual reproduction why is the offspring identical to the parent

there's only one parent

what is a clone

when the new cell has exactly the same genetic information as the parents

who reproduces asexually

bacteria, some plants and animals

how are gametes produced

by meiosis

in MEIOSIS what happens before the cell starts to divide

it duplicates its genetic material, forming two armed chromosomes so one arm of each chromosome is an exact copy of the other arm. After replication the chromosomes arrange themselves into pairs

in MEIOSIS what happens in the first division

the chromosomes pairs line up in the centre of the cell. the pairs are then pulled apart so each new cell only has one copy of each chromosome. some of the mothers and fathers chromosomes go into each new cell

in MEIOSIS

the chromosomes line up again in the centre of the cell. the arms of the chromosomes are pulled apart

what is the product of meiosis

you get four gametes each with only a single set of chromosomes in it. each of the chromosomes is genetically different from the others because the chromosomes get mixed up during meiosis and each gamete only gets half of them at random

what happens after two gametes have fused during fertilisation

the resulting cell divides by mitosis to make a copy of itself. mitosis repeats many times to produce lots of new cells in an embryo. as this embryo develops these cells start to differentiate into different types of specialised cells that make up a whole organism

what is the advantages of sexual reproduction?

offspring from sexual reproduction have a mixture of two sets of chromosomes producing genetic variation

Why is genetic variation important?

it can give a population of organisms a better chance of survival. A change in population could still kill some individuals but its likely variation will have led to some of the offspring surviving in the new environment

What are the advantages of asexual reproduction?

- only one parent needed
- time and energy efficient
- faster than sexual reproduction
- many identical offspring can be produced when conditions are favourable

how do parasites that can spread malaria reproduce?

when a mosquito carrying the parasite bites the human, the parasite can be transferred to the human. the parasite reproduces sexually and asexually when in the human host

How do fungi reproduce?

sexually and asexually

how do many species of fungus carry out reproduction?

- these species release spores that can become new fungi when they land in a suitable place.
- asexually-produced spores form genetically identical spores to the parent.
- sexually-produced spores introduce variation often due to unfavourable change in environment

How can plants reproduce asexually?

runners, bulbs

how many chromosomes are in every human body cell?

23 pairs

how is your sex determined?

Your sex is determined by whether you get an X or a Y chromosome from your father. Everyone receives an X from their mother. its the 23rd pair of chromosomes that determine your sex

what do men have as chromosomes?

an X and a Y chromosome. the Y chromosome causes male characteristics

what do women have as their chromosomes?

two X chromosomes. the XX chromosomes allows female characteristics to develop

what do the genes you inherit determine?

what characteristics you develop

what do different genes control?

The development of different characteristics

How are most characteristics controlled?

By several genes working together

what is an allele?

Different forms of a gene

What is homozygous?

organisms that have two identical alleles for a particular trait

What is heterozygous?

Organisms have two different alleles for a particular trait.

What is a dominant allele?

A form of a gene that is fully expressed, even when two different alleles are present. it determines the characteristic

What is a recessive allele?

An allele that is masked when a dominant allele is present

for an organism to display a recessive characteristic what has to happen?

both alleles have to be recessive

What is your genotype?

The combination of alleles you have

What do alleles do?

give rise to differences in inherited characteristics

What is cystic fibrosis caused by?

recessive allele

What is cystic fibrosis?

It is a genetic disorder of the cell membranes. Causes thick, sticky mucus to build up in air passages and pancreas.

What are carriers?

heterozygous individuals who carry the recessive allele but are phenotypically normal

If both parents carry the recessive allele that causes cystic fibrosis, the chance that their child will develop the disease is

1 in 4

What is polydactyly?

A genetic disorder where a baby's born with extra fingers or toes
Isn't life-threatening - doesn't cause any other problems

what is polydactyly caused by?

dominant allele

how is polydactyly inherited?

The allele is dominant. If a parent has polydactyly there is a 50% that offspring will have polydactyly.

how can genetic disorders be detected?

Embryonic screening

How does embryonic screening work?

a cell is removed from each embryo and its genes are analysed. its possible to get these genes from the womb

what are arguments against embryonic screening?

-Implies that people with genetic problems are 'undesirable' - this could increase prejudice.
-There may come a point where everyone wants to screen their embryos so they can pick the most 'desirable' one, e.g. they want a blue-eyed, intelligent boy.
-Screening is expensive.

what are arguments for embryonic screening?

-It will help to stop people suffering.
-Treating disorders costs the government and taxpayers a lot.
-There are laws to stop it going too far. At the moment parents cannot even select the sex of their baby unless it's for a health reason.

who is Gregor mendel?

father of modern genetics

What did Gregor Mendel do?

Breed different variations of garden pea plants in the 1800s and noted how characteristics in plants were passed on

what had mendel shown?

mendel had shown that height characteristics in pea plants was determined by separately inherited 'hereditary units' passed on from each parent.

what conclusions did mendel reach?

- characteristics in plants are determined by "hereditary units"
- Hereditary units are passed onto offspring unchanged from both parents
- hereditary units can be dominant or recessive and if both are present the dominant characteristic will be shown

what were different contributions of the understanding of genes today?

- in the late 18000s scientists became familiar with chromosomes. they could observe how they behaved

what is variation?

how species look different.

what are two types of variation

genetic and environmental

what causes variation?

the combination of genes from two parents

what characteristics are determined only by genes?

Eye colour
Blood group
Inherited disorders

what is environmental variation?

The environment and the conditions that organisms live and grow in causes differences between members of the same species

what affects most characteristics?

genes and environment

what introduce variation

mutation

what are mutations?

changes to the sequences of bases in DNA

what is the theory evolution

All of today's species have evolved from simple life forms that first started to develop over 3 billion years ago

Who is Charles Darwin?

created the theory of evolution

how did Darwin make his discovery?

with experiments discussion and new knowledge of fossils and geology

what is the survival of the fittest?

Organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive