4 Genetics 1 12/12 Flashcards
4.1.1 State that eukaryotic chromosomes are made of ___ and ________.
eukaryotic chromosomes are made of DNA and proteins.
4.1.2 Define gene, allele and genome.
gene: a heritable factor that controls a specific characteristic, consists of a seq. of DNA occupying a particular position on a chromosome
allele: an alternative form of a gene
genome: the whole of the genetic information of an organism, cell or organelle
4.1.3 Define gene mutation.
gene mutation: a change in the nucleotide seq. of a section of DNA coding for a particular feature
4.1.4 Explain the consequences of a base substitution mutation in relation to the process of transcription and translation, suing the example of sickle cell anaemia.
- base substitution: change of a single base in the seq. of DNA resulting in a change to a single mRNA codon during transcription
- Sickle cell anemia: GAG –> GTG
- –mRNA codon: GUG (glu instead of val)
- –aa alters the structure of hemoglobin by causing it to form insoluble strands –> sickle shape
- —-blocks capillaries, doesn’t hold as much O2
4.2.1 State that meiosis is a ______ ______ of _____ nucleus to form ______ nuclei.
meiosis is a reduction division of diploid nucleus to form haploid nuclei.
4.2.2 Define homologous chromosomes.
homologous chromosomes: the maternal and paternal copies of chromosomes that share the same structure and same genes at the same loci
4.2.3 Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells.
Meiosis I:
-prophase I: homologous chromosomes pair up(synapsis) to form a bivalent
–at the points of attachment(chiasmata), genetic material may be exchanged between non-sister chromatids, crossing over, leads to new gene combinations
-metaphase I:homologous chromosomes line up at equator
-anaphase I: homologous chromosomes split apart and move to opposite poles
-telophase I: cell splits into two haploid daughter cells as cytokinesis happens
(Meiosis II:
-prophase II: spindle fibres reform and reconnect to the chromosomes
-metaphase II: the chromosomes line up along the equator of the cell
-anaphase II: the sister chromatids split apart and move to(opposite poles
-telophase II: the cells split in two as cytokinesis happens) x2
produces 4 gametes
4.2.4 Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down’s syndrome (trisomy 21).
Non-disjunction: when chromosomes fail to separate (homologous pairs in anaphase I, sister chromatids in anaphase II) resulting in gametes with extra or missing chromosomes
extra chromosome gamete + normal gamete = zygote with trisomy (3)
down syndrome is trisomy 21
4.2.5 Sate that, in karyotyping, chromosomes are arranged in pairs according to their ____ and _______.
in karyotyping, chromosomes are arranged in pairs according to their size and structure.
4.2.6 Sate that karyotyping is performed using cells collected by ______ ____ _______ or __________, for pre-natal diagnosis of chromosome abnormalities.
karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.
4.2.7 Analyse a human karyotype to determine gender and whether non-disjunction has occurred.
Gender: XX, X = female XY, Y, XXY, XYY = male Non-disjunction: more or less than 2 homologous chromosomes
4.3.1 Define genotype, phenotype, dominant allele, recessive allele, codominant allele, locus, homozygous, heterozygous, carrier and test cross.
genotype: the symbolic representation of a pair of alleles possessed by an organism, typically represented by two letters
phenotype: the characteristics or traits of an organism
dominant allele: an allele that has the same effect on the phenotype when it is in the heterozygous state as when it is in the homozygous state
recessive allele: an allele that has an effect on the phenotype only when in the homozygous state
codominant allele: pairs of alleles that both affect the phenotype when present in the heterozygous state
locus: the particular position on the homologous chromosomes of a gene, each gene is found at a specific place on a pair of chromosomes
homozygous: having two identical alleles of a gene
heterozygous: having two different alleles of a gene, which results from the paternal and maternal alleles being different
carrier: an individual who has a recessive allele of a gene that does not have an effect on their phenotype
test cross: testing a suspected heterozygote plant/animal by crossing it with a know homozygous recessive.
