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Define haploid cell
- Cell containing only 1 set of chromosomes
- ie gametes
Define diploid cell
- Cell containing two sets of chromosomes
- ie somatic cells
- Incorrect number of a specific chromosome in a cell. Can affect multiple chromosomes
- ie Down syndrome
Define a monosomic cell
Cell resulting from a gamete without a specific chromosome. Resulting cell has only one of a specific chromosome
Define trisomic cell
- Cell with 3 of a certain chromosome.
- i.e Down syndrome
- Where homologous chromosomes fail to separate during meiosis I OR
- Sister chromatids fail to separate during meiosis II resulting in aneuploid gametes
What is Klinefelter syndrome? Symptoms?
- Where somatic cells contain an extra X chromosome - XXY.
- Males who are taller, feminine, sterile, may see breast development
What is Turner syndrome? Symptoms?
- Where somatic cells contain only an X chromosome - XO.
- Females who are shorter, sterile, may exhibit brown spots on skin
What is a Barr body? How does it arise?
Barr body is a region of hetero-chromatin close to the nuclear envelope found in females following X inactivation.
List n, number of cells and number of chromosomes at each step of meiosis.
- Prophase I - 2n=46, duplicated, 1 diploid cell
- Telophase I - n=23, duplicated, 2 haploid cells
- Telophase II n=23, unduplicated, 4 haploid cells
Removal/loss of a chromosomal segment
Repeat of a chromosomal segment on a chromosome
Reversal of a chromosomal segment on a chromosome
Segment transferred from one chromosome to another.
Define reciprocal translocation.
Exchange of chromosomal segments between two chromosomes
- Possession of multiple ENTIRE sets of of chromosomes.
- i.e a tetraploid has 4 sets of chromosomes
Define incomplete dominance.
- Where both alleles in a heterozygous sample are shown in phenotype AT REDUCED LEVELS
- ie Snap dragon flower shows reduced red pigment in RW heterozygote
Where phenotypes of both alleles are seen in a heterozygous sample
- Gene at one locus affects another.
- i.e Labradors can have black or brown hair pigment - only if gene for hair pigment is present at another locus
- Where there are multiple alleles for a gene.
- i.e eye colour - blue, brown, green - however, each human only has two alleles.
- Ability of a gene to have multiple effects
- i.e sickle cell anemia
Describe how environmental factors can contribute to variation in ratios predicted by Mendelian genetics.
- Environment can cause phenotypic variation in individuals with same genotype
- i.e, hydrangea flowers with same genotype are different colours depending on soil pH
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