unit 3 part 2. Flashcards
define meiosis
the division of a diploid nucelus to preduce foru haploid nuclei
what happens before meiosis? in interphase
DNA is duplicated so that sister chromatids are arranged to become homologous chromosomes. these then arrange to form paris called bivalents and are held together by chiasmata
what happens in meiosis 1?
prophase 1: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs.
metaphase 1:
Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
anapahse 1:
Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
telophase 1:
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
what happens in meiosis 2?
P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
Explain how meiosis leads to genetic variation in gametes.
Crossing over in prophase I
Random assortment of chromosomes in metaphase I
Random fusion of gametes from different parents
Define non-disjunction.
Nondisjunction is when chromosomes fail to separate properly, leading to gametes with one extra or one missing chromosome. This can lead to down syndrome and other genetic diseases.
Describe the two procedures for obtaining fetal cells for production of a karyotype
Chorionic Villi Sampling
Sample of chorionic villus (placenta tissue) is removed via a tube inserted through the cervix.
Approx 1% chance of miscarriage
Done at around 11 weeks
Amniocentesis
Involves the extraction of a small amount of amniotic fluid with a needle
Conducted at 16 weeks
0.5% chance of miscarriage
State an example of a dominant and recessive allele found in pea plants.
Dominant trait: flower color: purple, plant height: tall, seed color: yellow, seed shape: round
Recessive trait: flower color: white, plant height: short, seed color: green, seed shape: wrinkled
Define codominant alleles.
Co-dominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual. Ex. AB blood group
Define “carrier” as related to genetic diseases.
An organism that inherits the recessive allele of a gene, but does not show any symptoms of the disease because they also have the dominant (normal functioning) allele.
Explain sickle cell anaemia as an example of a genetic disease caused by codominant alleles.
Sickle cells anemia is a rare disease where red blood cells become thin and elongated. If a person has one copy of the sickle cell allele, half of their red blood cells will misshapen. The alleles are codominant since both normal and sickle cell shapes are seen in a heterozygous individual.
Define sex linkage + examples
When a gene controlling a characteristic is located on a sex chromosome.
Common examples are colorblindness and hemophilia (both recessive)
Use correct notation for sex linked genes.
For sex linked genes, X and Y are used for the notation of whether it is a female or male trait.
The chromosome is written as a subscript.
Xr = red eye
List five example genetic diseases.
Cystic fibrosis (autosomal recessive)
PKU (autosomal recessive)
Huntington’s disease (autosomal dominant)
Hemophilia (sex linked recessive, on x Chromosome )
Red-green colorblindness (sex-linked recessive, on the X chromosome)
Define monohybrid, true breeding, hybrid, F1 and F2.
Monohybrid - a genetic cross between two individuals tracking one gene of interest
True breeding - organisms that have been bred to have a homozygous genotype
F1 generation - the offspring of the parent generation cross
F2 generation - the result of a cross between two F1 individuals