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Level 1 Genetics, basic meiosis, and mitosis, definitions, etc.
Genetic Code
Chromosomes |
structures made of DNA molecules that contain the genes. |
Genes |
sections of chromosomes/DNA that code for our characteristics |
Alleles |
alternatives forms of a gene |
Trait |
a genetically determined characteristic or condition |
Homologous Pair |
a pair of 2 chromosomes: 1 from the mother and 1 from the father |
Organism |
an individual animal, plant, or single-celled life form. |
Genotype |
the combination of alleles that an organism has |
Phenotypes |
the characteristic produced by the genotype |
Dominant Allele |
always expressed (shows the trait) if present (eg. B) |
Recessive Allele |
only expressed when the dominant allele is absent (eg. b) |
Homozygous |
having two identical alleles (eg. bb) |
Heterozygous |
having two different alleles (eg. Bb) |
DNA carries the genetic information in a cell. A gene and an allele are both made of DNA. A gene is a length of DNA that codes for a particular characteristic, whereas an allele is the alternative form of a gene containing a different base sequence. A gene for a characteristic consists of two alleles.
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DNA Structure
DNA |
genetic material stored in the nucleus of cells |
Nucleus |
contains the chromosomes |
DNA Structure |
double helix which consists of nucleotide subunits |
See diagram of DNA structure here: |
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Complementary Base Pairing |
there are four bases, two pairs: |
Adenine (A) |
Thymine (T) |
Guanine (G) |
Cytosine (C) |
Remember adenine pairs with thymine as 'Apples grow on Trees'.
Remember guanine pairs with cytosine as 'Carrots grow in the Ground'.
Variation
Why is variation important? |
-Variation increases the chance of survival of a species if there is a change in the environmental pressure. |
-Without variation in a species any sudden environmental change can mean that no individual has a phenotype that allows it to survive, causing the species to become extinct. |
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Pure Breeding
An organism that always passes down certain phenotypic traits to its offspring of many generations. The organisms's parents and ancestors all belong to the same breed. |
Pure bred genotypes are always homozygous. |
genotype of parent 1: PP, genotype of parent 2: PP |
genotypic ratio of the offspring: 4PP, 0pp, 0Pp |
phenotypic ratio of the offspring: 4purple, 0white |
In pigs, curly tails are dominant. To work out if a curly-tailed pig is homozygous dominant or heterozygous for this trait, mate the curly-tailed pig with a straight-tailed pig. We know the straight-tailed pig's genotype is tt. If any offspring have straight tails we know the curly-tailed pig is heterozygous because they must be carrying the recessive allele for a recessive offspring to be produced. If no offspring have straight tails it is likely that the curly-tailed pig is TT.
Meiosis
Haploid |
a cell that contains a single set of chromosomes. |
Meiosis |
a type of cell division that produces 4 gametes (sex cells- sperm and egg) each with only half the number of chromosomes (23). |
There are two main ways meiosis produces variation: |
1. Crossing Over |
2. Independent Assortment |
These steps are important because they mix up allele combinations, causing variation. |
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