AS90948 - Genetics - NCEA - lvl 1
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What is the purpose of mitosis?
Growth and repair.
What does mitosis produce?
Two genetically identical daughter cells.
How many chromosome sets are in a diploid cell?
Two complete sets (2n).
Where does mitosis occur?
In somatic (body) cells.
What is the purpose of meiosis?
To produce gametes (sperm and egg cells).
What does meiosis produce?
Four genetically different cells.
How many chromosome sets are in a haploid cell?
One set (n) — half the diploid number.
Where does meiosis occur?
In the testes and ovaries.
What are chromosomes made of?
DNA.
What do chromosomes carry?
Genes.
What do genes code for?
Proteins.
What is an allele?
An alternative version of a gene.
How many DNA bases code for one amino acid?
Three bases (a triplet).
What determines which protein is produced?
The sequence of bases in a gene.
What can small DNA sequence differences create?
Different alleles, often resulting from mutations.
What is a homozygous genotype?
Two identical alleles, e.g. BB or bb.
What is a heterozygous genotype?
Two different alleles, e.g. Bb.
What does pure breeding mean?
An individual consistently produces offspring resembling the parent; it is homozygous for that trait.
What is a dominant allele?
An allele expressed whenever it is present.
What is a recessive allele?
An allele expressed only when no dominant allele is present.
What does it mean if an allele is masked?
A dominant allele hides the effect of a recessive allele.
What is a genotype?
The combination of alleles an organism has.
What is a phenotype?
An organism's observable characteristic or appearance.
How are gametes shown in a Punnett square?
Write the single alleles along the top and side.
What does a Punnett square predict?
Possible offspring genotypes, phenotypes and their probabilities.
Why might actual offspring ratios differ from a Punnett square?
Fertilisation is random, so predicted ratios are probabilities, not exact numbers.
What happens to predicted ratios with more offspring?
Results are more likely to get closer to the predicted ratios.
What is crossing over?
Homologous chromosomes exchange sections during meiosis.
What is independent assortment?
Homologous chromosome pairs line up randomly, creating different chromosome combinations in gametes.
What is the sugar-phosphate backbone?
The outer structure of a DNA strand.
What are the complementary DNA base pairs?
A pairs with T; C pairs with G.
What is a DNA nucleotide made of?
A sugar, a phosphate group and a base.
How does DNA replicate?
The strands separate; complementary nucleotides pair with exposed bases; enzymes join them and the DNA rewinds.
Why must DNA replicate accurately?
So daughter cells receive the same DNA as the parent cell.
What is a mutation?
A permanent change in DNA sequence or chromosome number.
How can a base-sequence mutation affect an organism?
It may change the amino acid sequence, producing a different protein.
When can a mutation be inherited?
When it occurs in a gamete (sex cell) and is passed to offspring.
Why is there genetic diversity in a population?
Meiosis creates different combinations of alleles.
How can genetic variation help with disease resistance?
Some individuals may have alleles that make them more resistant to a disease.
How can natural selection lead to evolution?
Better-adapted individuals survive and reproduce, passing on helpful alleles; these become more common.
What is the nucleus?
The cell part that contains chromosomes.
What is DNA?
Deoxyribonucleic acid: the substance carrying an organism's genetic information.
What is a chromosome?
A threadlike structure of DNA and protein in the nucleus; carries genes.
What are homologous chromosomes?
Chromosomes with the same structural features and pattern of genes.
What is a karyotype?
A photograph of an individual's chromosomes, arranged by size.
What is a gene?
A short length of DNA carrying the code for a particular trait or cell activity.
What is an allele?
A different form of the same gene; it may be dominant or recessive.
What is a DNA base?
One of the DNA bases: cytosine, guanine, adenine or thymine.
What is a nucleotide?
The basic unit of DNA: a sugar, phosphate group and base.
What is DNA's role?
It carries instructions to the next generation and determines phenotype.
What is a trait?
A genetically determined characteristic.
What is variation?
Differences between organisms in a population; continuous or discontinuous.
What is mitosis?
Body-cell division for growth and repair; produces two genetically identical cells.
What is meiosis?
Cell division in testes and ovaries; produces four genetically different gametes.
What is a gamete?
A reproductive cell containing half the number of chromosomes of the parent cell.
What is a zygote?
A fertilised egg containing the full set of chromosomes.
What is asexual reproduction?
Reproduction involving one parent; offspring are genetically identical.
What is sexual reproduction?
Reproduction involving two parents; offspring differ from parents and each other.
What is a clone?
An organism produced asexually from one parent; genetically identical to parent and siblings.
What is a trait?
A genetically determined characteristic.
What is a mutation?
A permanent change in the base sequence of DNA.
What is an allele?
A different form of the same gene; it may be dominant or recessive.
What is a genotype?
The particular alleles of an organism.
What is a phenotype?
Observable characteristics resulting from an individual's genotype.
What does pure breeding mean?
Homozygous individuals always produce the same offspring when crossed together.
What does homozygous mean?
An individual has two identical alleles for a particular trait.
What does heterozygous mean?
An individual has two different alleles for a particular trait.
What is a test cross?
Cross an unknown-genotype organism with a homozygous recessive organism to determine its genotype.
What is a dominant allele?
An allele expressed even when only one copy is present; written with a capital letter (A).
What is a recessive allele?
An allele expressed only when two copies are present; written with a lower-case letter (a).
What is a pedigree chart?
A family-tree diagram showing the phenotypes of related individuals.
What does haploid mean?
Having a single set of chromosomes (n).
What does diploid mean?
Having a full set of chromosomes (2n), with a pair of each chromosome type.
What is a carrier?
An individual carrying a recessive allele who does not show the trait but can pass it on.
What are amino acids?
The basic building blocks of proteins.
What is a double helix?
The DNA structure: two strands of nucleotides wound around each other.
What is fertilisation?
The joining of male and female gametes.
What is offspring?
The product of reproduction: a new organism produced by one or more parents.
What are proteins?
Molecules made up of amino acids; there are many types with important roles in living systems.
What is a Punnett square?
A chart showing all possible allele combinations from a genetic cross.
What is semi-conservative replication?
Each new DNA double helix has one original strand and one newly made strand.
What are sex chromosomes?
The X and Y chromosomes that determine an individual's sex.
What is crossing over?
The exchange of genetic material between homologous chromosomes.
What is a mutation?
The process responsible for forming new alleles.
What are the F1 and F2 generations?
F1: offspring of the BB × bb cross; F2: offspring of the F1 generation.
What is a changing environment?
Conditions such as pest infestation, disease, drought or flood.
What is independent assortment?
Each homologous chromosome pair lines up at the equator independently of other pairs.