Reproduction (6.1) (M) Flashcards
What is meiosis?
Reduction division in a cell in which the chromosome number is halved
What is the main difference between meiosis and mitosis?
meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed
What is sexual reproduction?
the joining (fusion) of male and female gametes
so two parents
there is mixing of genetic information which leads to variety in the offspring
What are gametes?
sex cells
Describe sexual reproduction in animals
the joining (fusion) of sperm (male gamete) and egg (female gamete) cells
Describe sexual reproduction in flowering plants?
the joining (fusion) of pollen (male gamete) and egg (female gamete) cells
How does sexual reproduction lead to a variety in the offspring?
there is mixing of genetic information which leads to variety in the offspring
The formation of gametes involves which process?
meiosis
What is asexual reproduction?
Reproduction involving only one parent and no fusion of gametes
so there is no mixing of genetic information, which leads to genetically identical offspring (clones)
Is there mixing of genetic information in asexual reproduction? What does this lead to?
No
leads to genetically identical offspring (clones)
Which process is involved in asexual reproduction?
Only mitosis is involved
Cells in (…) organs divide by (…) to form (…)
reproductive
meiosis
gametes
Describe the process of meiosis (e.g. a cell dividing to form gametes)?
- copies of the genetic information are made
- the cell divides twice to form four gametes, each with a single set of chromosomes (haploid)
- all gametes are genetically different from each other
a diploid is a cell with two sets of chromosomes in pairs, one from each parent
What is fertilisation
(different) gametes joining to restore the normal number of chromosomes (by forming a zygote)
What is a zygote?
a fertilised egg cell
Fertilisation produces a new cell (zygote), by which process does this new cell divide by?
mitosis
After fertilisation and mitosis, what happens to the number of cells?
they increase
As the embryo develops cells (…)
differentiate
What is DNA?
A polymer made up of two strands forming a double helix
What does the chemical DNA make up?
The genetic material in the nucleus of a cell
Where is DNA contained?
in chromosomes
What is a gene?
a small section of DNA on a chromosome, that codes for a particular sequence of amino acids, to make a specific protein
How is a protein made?
Each gene codes for a particular sequence of amino acids, to make a specific protein
What is the genome of an organism?
the entire genetic material of that organism
Has the whole human genome now been studied? What does this mean?
Yes
this will have great importance for medicine in the future
3 needed
What are the important uses from the understanding of the human genome?
- search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past
What are nucleotides?
molecules consisting of a common sugar and phosphate group with one of four different bases attached to the sugar
How many nucleotides is DNA made up of?
four different nucleotides
What are the four bases of DNA?
A, C, G and T
What forms the code for a particular amino acid?
A sequence of three bases
What does the order of the bases control?
the order in which amino acids are assembled to produce a particular protein
What do long strands of DNA consist of?
Alternating sugar and phosphate sections. Attached to each sugar is one of the four bases
What is a DNA polymer made up of?
repeating nucleotide units
What is protein synthesis?
The production of proteins from amino acids, which happens in the ribosomes of the cell.
In complementary strands, what do pairs of bases always form?
In the complementary strands a C is always linked to a G on the opposite strand and a T to an A
What determines the protein synthesised by a gene?
The order of bases in DNAs (in threes), which code for one specific amino acid
- which is then assembled in a particular sequence to produce a specific protein*
- may lead to change in gene expressed i.e. blue eye colour*
Describe the process of protein synthesis?
Bases of DNA form code for making a particular protein
A sequence of three bases in the DNA codes for a particular one amino acid
A copy of the sequence of bases is made
It leaves the nucleus and binds to the ribosome
Specific amino acids brought to ribosome on carrier molecules
Amino acids are assembled into order based on code to form protein
What do carrier molecules do in protein synthesis?
They bring specific amino acids to add to the growing protein chain in the correct order
What happens when the protein chain is complete?
it folds up to form a unique shape
What does the unique shape of the protein chain enable?
the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen
What are mutations often a result of?
mistakes made when copying DNA
Mutations occur (…)
continuously
Explain how often mutation alter the protein?
Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed
A few mutations code for what?
an altered protein with a different shape
A few mutations code for an altered protein with a different shape. What may this led to?
An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength
Do all parts of DNA code for proteins?
No - not all parts of DNA code for proteins
Non-coding parts of DNA do what? So…
they can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed
What is a gamete?
A sex cell (sperm in males and ova/eggs in females)
What is the chromosome?
The structure made of DNA that codes for all the characteristics of an organism
2 facts needed
What is a gene?
The section of DNA that codes for a protein, and is inherited from our parents
What is an allele?
one different form of a gene
What does a homozygote mean?
An individual with identical alleles for a characteristic
What does a heterozygote mean?
An individual with different alleles for a characteristic
What is a phenotype?
the physical appearance of an individual for a particular visible characteristic
What is a genotype?
The alleles that an organism has for a particular characteristic, usually written as letters
- inherited from parents*
- genotype - all the alleles for a characteristic, phenotype - the visible appearance due to this*
2 needed
What are examples of characteristics that are controlled by a single gene?
- fur colour in mice
- red-green colour blindness in humans
How is something expressed as a phenotype?
The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype
What is a dominant allele?
the allele that is always expressed, even if only one copy is present
What is a recessive allele?
the allele that is only expressed if two copies are present (therefore no dominant allele present)
When is an organism homozygous for a trait?
if the two alleles present are the same
When is an organism heterozygous for a trait?
if the alleles are different
What are most characteristics are a result of?
multiple genes interacting, rather than a single gene
most phenotype features are the result of multiple genes rather than single gene inheritance
Use direct proportion and a ratio to express the outcome of this genetic cross
Direct proportion: Half of offspring have combination Aa and half have combination aa
Ratio: ratio of Aa to aa is 1:1
White fur is recessive. Grey fur is dominant. Two mice that are heterozygous for the fur colour gene mate. Determine the probability that the offspring will have grey using a punnet square?
CIRCLE AA, Aa and Aa / genotypes that gives answers!!!!
75% probability
Some disorders can be developed due to life choices, others may be (…)
inherited
What are inherited diseases caused by?
the inheritance of certain alleles
What are two examples of inherited disorders?
polydactyly and cystic fibrosis
What is polydactyly?
having extra fingers or toes
Polydactyly is caused by a (…) allele
dominant
What is cystic fibrosis?
a disorder of cell membranes
Cystic fibrosis is caused by a (…) allele
recessive
What is embryo screening?
Embryos checked for genetic/inherited disorders
Involve taking a sample from he growing fetus
Why might someone get an embryo screened?
to see if they are carriers of genetic disorders
4 needed
What are the advantages of embryo screening?
- prevent child with disorder from future suffering
- embryo cells could be used in stem cell treatment
- reduces cost long-term (treating children with inherited disorders is costly)
- allows time for parents to become prepared
2 needed
What are disadvantages of embryo screening?
- Some people believe it is unethical to kill an embryo - which is a potential life
- procedure is expensive
What are carriers?
Heterozygous individual that do not have (express) an inherited disorder themselves, as the gene (allele) is recessive, but could pass it onto their offspring who might inherit it
What property of DNA allows it to replicate itself?
The complimentary base paring (A always pairs with T, C always pairs with G)
Why is it considered unacceptable to use reproductive technology to allow parents to select the gender of their offspring?
Using technology to select for a desired characteristic is not the same as preventing a child from having a life-threatening condition
+ could be dangerous for mother
What is the difference between and allele and gene?
alleles are different forms of a gene controlling a characteristic and occupying the same site on homologous chromosomes
genes are the units of DNA/sites on chromosomes carrying the information that determines characteristics
5 marks
Strand K shows a mutation in the DNA which has caused syndrome H.
The enzyme IDUA helps to break down a carbohydrate in the human body.
The enzyme IDUA produced from Strand K will not work.
Explain how the mutation could cause the enzyme not to work.
(mutation) changes from C to T DNA code
changes the amino acid
change the protein
so it forms different shape/changed active site
so enzyme no longer fits substrate/carbohydrate
ask about MS for this question
What is a mutation?
A change in the DNA
What is the function of DNA?
Contains a code for a particular sequence of amino acids, to form a specific/particular protein
Why is DNA described as a polymer?
consist of many (joined) monomers/nucleotides
The length of a DNA double helix increases by 0.34 nm for every pair of nucleotides.
The total number of nucleotides in a human body cell is 1.2 × 1010.
Calculate the total length of double helix in a human body cell. Give your answer in metres
0.34 x 1.2 x 1010
= 4.08 x 109
(4.08 x 109) / 109
= 4.08m
4.08 / 2 (due to base pairs)
= 2.04m
Why would it be beneficial to take 5 eggs from an ovary rather than one in embryo screening?
Greater chance on healthy egg/embryo/child
How does a chromosome become two strands?
DNA replication / copies f the genetic information were made
Explain why each chromosome must become two strands before the cell divides?
One copy of each chromosome to each offspring cell
so each offspring set receives the same amount/compete set of genetic material
one needed
Why is DNA analysis for cancer beneficial?
- to determine if the cancer is genetic (or caused by lifestyle factors)
- to inform / help treatment
- to allow embryo screening to ensure allele is not passed on
- to inform relatives if they have inherited (affected) gene / allele
- to detect cancer early or before symptoms show
- to understand cause of the cancer
Why was both IVF and embryo transfer used rather than allowing organisms/people to mate naturally?
takes less time
