Inheritance, Genes & Cell Division (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Biology): Flashcards
Exam code: 0654 & 0973
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Gene
A length of DNA that codes for a particular protein.
Chromosome
A thread-like structure made of DNA, carrying many genes.
Allele
A different version (form) of the same gene.
A gene is a length of that codes for a protein.
DNA
are made of DNA and carry many genes.
Chromosomes
How are DNA, genes and chromosomes related?
DNA is coiled up to form chromosomes.
A gene is a section of DNA on a chromosome that codes for a protein.
What are the sex chromosomes of human females and males?
Females have two X chromosomes (XX).
Males have one X and one Y chromosome (XY).
Human females have the sex chromosomes .
XX
Human males have the sex chromosomes .
XY
What ratio of males to females does a genetic cross of sex chromosomes predict?
A 1:1 ratio (50% male : 50% female).
Which parent determines the sex of the child, and why?
The father.
He can pass on either an X or a Y chromosome, whereas the mother can only pass on an X.
What do 'homozygous' and 'heterozygous' mean?
Homozygous: having two identical alleles of a particular gene.
Heterozygous: having two different alleles of a particular gene.
An organism with two different alleles of a gene is described as .
heterozygous
What is a pure-breeding organism?
An organism that is homozygous for a characteristic, so it always passes on the same allele.
A human diploid body cell contains pairs of chromosomes.
23
Mitosis
Nuclear division giving rise to genetically identical cells.
Where is mitosis used in the body (Extended)?
Growth.
Repair of damaged tissues.
Replacement of worn-out cells.
Asexual reproduction.
Mitosis produces two genetically daughter cells.
identical
How does the chromosome number of the daughter cells compare to the parent cell in mitosis?
The daughter cells have the same number of chromosomes as the parent cell (they are diploid).
What happens to the DNA before mitosis (Extended)?
The DNA (chromosomes) is copied/replicated exactly before the cell divides.
Meiosis
Reduction division in which the chromosome number is halved, producing genetically different gametes.
What is meiosis used to produce?
Gametes (sex cells).
Meiosis produces cells with the number of chromosomes (haploid).
half
Compare mitosis and meiosis (Extended).
Mitosis produces two genetically identical diploid cells for growth and repair.
Meiosis produces four genetically different haploid gametes.
produces four genetically different gametes.
Meiosis
Why does meiosis lead to variation?
It produces genetically different gametes, which leads to genetic variation in the offspring.
Dominant allele
An allele that is expressed even if only one copy is present.
Recessive allele
An allele that is only expressed when two copies are present.
Genotype
The alleles an organism has for a characteristic.
Phenotype
The observable characteristics (features) of an organism.
is the genetic make-up (the alleles) of an organism.
Genotype
An organism with two identical alleles for a gene is described as .
homozygous
How do you use a Punnett square to predict offspring (Genetic Diagrams)?
Write the alleles of each parent's genotype.
Put one parent's alleles along the top and the other's down the side.
Combine them in the boxes to show the possible offspring genotypes.
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