Reproduction Flashcards
All 51 cards in this deck
What is sexual reproduction?
Reproduction involving the fusion of male and female gametes from two parents, mixing genetic information so the offspring show variation.
What is asexual reproduction?
Reproduction involving only one parent and no fusion of gametes, so there is no mixing of genetic information and the offspring are genetically identical clones.
Name the male and female gametes in animals.
Sperm (male) and egg cell / ovum (female).
Name the male and female gametes in flowering plants.
Pollen grain (male) and egg cell in the ovule (female).
Which type of cell division is involved in asexual reproduction?
Only mitosis.
True or false? In asexual reproduction genes are not passed from parent to offspring.
False. Genes are passed on in both types of reproduction; in asexual reproduction the offspring receive an identical copy of the parent's genes.
Where in the body does meiosis take place?
In the reproductive organs (e.g. testes and ovaries), to form gametes.
How many cells does meiosis produce from one cell, and what are they like?
Four gametes, all genetically different, each with a single set of chromosomes (half the normal number).
How does meiosis produce gametes that are genetically different?
A random chromosome from each pair goes into each gamete, giving different combinations of chromosomes.
What are the steps by which meiosis halves and fertilisation restores the chromosome number?
e.g. a human cell with 46 chromosomes- Chromosomes are copied and the cell divides twice: 4 gametes, each with 23 chromosomes.
- Two gametes fuse at fertilisation: 23 + 23 = 46 chromosomes.
- The new cell divides by mitosis to form an embryo, keeping 46 chromosomes in every cell.
What type of cell division does the fertilised egg use as it grows into an embryo?
Mitosis — the number of cells increases and, as the embryo develops, the cells differentiate.
True or false? Meiosis produces two genetically identical cells.
False. Meiosis produces four genetically different cells; mitosis produces identical cells.
Give two advantages of sexual reproduction.
It produces variation in the offspring, and if the environment changes this variation can give a survival advantage.
Give two advantages of asexual reproduction.
Only one parent is needed and it is faster, using less time and energy, so many identical offspring can be produced when conditions are favourable.
Give one disadvantage of asexual reproduction.
There is no genetic variation, so the whole population can be wiped out by the same disease or environmental change.
Give one disadvantage of sexual reproduction.
Two parents are needed, so it takes more time and energy (e.g. to find a mate) and is slower than asexual reproduction.
How does the malarial parasite use both types of reproduction?
It reproduces asexually in the human host and sexually in the mosquito.
Give two examples of plants that reproduce both sexually and asexually.
Strawberry plants (runners asexually, seeds sexually) and daffodils (bulbs asexually, seeds sexually).
What is DNA and where is it found in a cell?
The chemical that genetic material is made of — two strands coiled into a double helix, found in the nucleus in structures called chromosomes.
Why is DNA described as a polymer?
It is a long molecule made from many nucleotides (repeating units) joined together.
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.
What is the genome of an organism?
The entire genetic material of that organism.
Give two reasons why understanding the human genome is important.
It helps scientists search for genes linked to disease and understand and treat inherited disorders; it can also be used to trace human migration patterns.
What is a DNA nucleotide made of?
A common sugar and a phosphate group, with one of four bases (A, C, G or T) attached to the sugar.
What are the base pairing rules in DNA?
e.g. one strand reads A–C–GA always pairs with T, and C always pairs with G, so the complementary strand reads T–G–C.
How many bases code for one amino acid, and what does the order of bases control?
Three bases (a triplet) code for one amino acid; the order of bases controls the order in which amino acids are assembled to make a particular protein.
Where are proteins synthesised in a cell, and what brings the amino acids?
On ribosomes, using a template from the gene; carrier molecules bring specific amino acids to add to the growing protein chain in the correct order.
How can a change (mutation) in the base sequence of a gene change the protein made?
It can change the sequence of amino acids, which changes the protein's shape — e.g. an enzyme's active site may no longer fit its substrate, so the protein cannot do its job.
True or false? All of the DNA in a cell codes for proteins.
False. Some DNA is non-coding; variations in non-coding DNA can switch genes on and off and so affect how genes are expressed.
What is an allele?
A different form of a gene.
What is the difference between a dominant and a recessive allele?
A dominant allele is always expressed, even if only one copy is present; a recessive allele is only expressed if two copies are present.
What do homozygous and heterozygous mean?
Homozygous = the two alleles for that gene are the same; heterozygous = the two alleles are different.
What is the difference between genotype and phenotype?
Genotype is the combination of alleles an organism has (e.g. ); phenotype is the characteristic that is expressed.
In a family tree, two parents who do not have a disorder have a child who does. What does this show about the allele causing it?
The allele is recessive, and both parents must be heterozygous carriers.
What is polydactyly and what type of allele causes it?
Having extra fingers or toes; it is caused by a dominant allele.
What is cystic fibrosis and what type of allele causes it?
A disorder of cell membranes; it is caused by a recessive allele.
What is a carrier of an inherited disorder?
A heterozygous person who has one recessive disorder allele but does not have the disorder, and can pass the allele to their children.
True or false? A child can only inherit polydactyly if both parents have polydactyly.
False. Polydactyly is caused by a dominant allele, so inheriting one copy from one parent is enough.
Give one argument in favour of embryo screening.
It stops people suffering from a genetic disorder (and treating disorders is expensive for the health service).
Give one argument against embryo screening.
It implies that people with genetic disorders are undesirable, and unwanted embryos are destroyed; it could also lead to people choosing other 'desirable' characteristics.
How many pairs of chromosomes are in an ordinary human body cell, and what do they control?
23 pairs — 22 pairs control characteristics only, and one pair carries the genes that determine sex.
What are the sex chromosomes of a human female and of a human male?
Female = XX, male = XY.
Which parent's gamete determines the sex of a child, and why?
The father's — sperm carry either an X or a Y chromosome, while all egg cells carry an X.
What probability of a male child does a cross between XX and XY predict?
(50%), a 1 : 1 ratio of male to female offspring.
True or false? An ordinary human body cell contains 23 chromosomes.
False. It contains 23 pairs, which is 46 chromosomes; a gamete contains 23.
True or false? Most human characteristics are controlled by a single gene.
False. Most characteristics are the result of multiple genes interacting; only a few, such as red-green colour blindness, are controlled by a single gene.
True or false? The genome of an organism includes the non-coding DNA as well as the genes.
True. The genome is the entire genetic material of the organism.
What mass of DNA does a human sperm cell contain compared with a human body cell?
e.g. a body cell containing g of DNA
Half as much, because a gamete has one set of chromosomes.
e.g. the sperm cell contains g
To change a length of DNA given in nanometres (nm) into metres (m), what do you divide by?
(), because 1 nm m.
What are the steps to complete a Punnett square for a monohybrid cross and state the offspring phenotypes?
e.g. , where B = black fur (dominant) and b = white fur (recessive)
- Write one parent's gametes along the top, the other's down the side: B and b; B and b
- Fill the four boxes by combining the alleles: BB, Bb, Bb, bb
- Read off the phenotypes: 3 black : 1 white
True or false? A cross between two heterozygous parents gives offspring genotypes in the ratio 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.
True. e.g. gives BB, Bb, Bb, bb.