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Meiosis and the Origins of Human Life - Coggle Diagram
Meiosis and the Origins of Human Life
Meiosis
Stages
Prophase 1 - The homologous chromosomes condense and cross over (exchange) genetic info.
Metaphase 1 - Tetrads (pairs of homologous chromosomes) align at the center (spindle fibers attach to the centromeres).
Anaphase 1 - The homologous chromosomes are split by spindle fibers pulling them away.
Telophase 1 - 2 new nuclei form around the two sets of chromsomes, the cytoplasm splits, andc two haploid cells are made.
Meiosis II
Prophase II - chromsomes condense and spindle fibers form.
Metaphase II - chromsomes line up at the center of the cell. Spindle fibers attach to the centromeres.
Anaphase II - chromsomes are separated into sister chromatids by spindle fibers.
Meiosis I
Telophase II - 2 new nuclei form around the 2 sets of chromatids. As Meiosis II happens in both of the haploid cells from Meiosis I, 4 new haploid cells are finally made by dividing the two previous haploid cells.
Mendel's Laws/Genetics
Independent Assortment: Genes are inherited independently of each other, unless part of a linkage group (groups of genes known to be inherited together).
Law of Segregation: genes separate from each other, meaning that each gamete contains one allele for each gene.
Punnett Squares measure the probability of certain genotypes in offspring on a 2X2 grid.
Dominant alleles (variations of genes) mask recessive alleles. Dominant alleles are uppercase letters in the genotype, and reverse alleles are lowercase letters. Dominant alleles only need to be one of the two alleles in the genotype to be expressed whereas two recessive alleles are needed to express a recessive trait.
Karyotypes represent the total number of chromosomes and the sex chromosomes of an individual. You can identify chromosomal disorders by looking for an abnormal number of autosomal or sex chromosomes in the karyotype.
Pedigrees show a family tree and can be used to track the inheritance patterns of certain traits, especially diseases.
Epistatic genes mask any previous dominant or recessive genes if two of the same alleles for the gene are present.
Codominance: No allele is able to mask the expression of another allele. This results in phenomena such as AB blood, where A and B are codominant
Incomplete dominance: when the dominant gene doesn't fully mask the expression of the recessive gene, resulting in phenomena such as the offspring of a purebred red and purebred white flower to become pink.
Sexual Reproduction
Gametes are sex cells. They're sperm in males and eggs in females.
After Meiosis 1, fertilization occurs when a haploid sperm cell fertilizes a haploid egg to create a diploid zygote.
Haploid cells have half the amount of required chromosomes to survive. Diploid cells have all the chromosomes needed for an organism to survive, half from mom and half from dad.
Sex chromosomes determine the sex of an offspring via an X-Y system. In females, they’re XX, and XY for males.
Chromosomal Disorders
Main Idea: Chromosomal Disorders arise from disparities in autosomal or sex chromosome count.
Down Syndrome: due to a trisomy in chromosome 21.
Cri Du Chat: caused by a deletion on chromosome 5's short arm.
Klinefelter's Syndrome: Caused by an extra X chromosome.
Deletion: genetic material is missing.
Insertion: There's extra genetic material.
Translocation: the pieces of two chromosomes break off and then swap places with one another.
Robertsonian Translocation: happens with chromosomes with one very short and one long arm; the short arms of both chromosomes come off, and the remaining long arms fuse together. The short arms contain little genetic info, so breaking them off doesn't make much of an impact.
Gender-Related Disparities
Testosterone: a hormone produced to promote male reproductive development.
Androgen: a group of hormones that promote male reproductive development (i.e. testosterone).
Androgen Receptors: these relieve androgen in order to promote male development.
SRY Gene: gene found on the Y chromosome that codes for a transcription factor which kickstarts fetal production of male gonads, the testes.
People can be genetically male (XY) but still be assigned female at birth, as they may not have enough androgen receptors to receive the testosterone they make to start male development. In addition, a mutation of the SRY gene could also not promote male development.
People can be genetically female (XX) but still be assigned male at birth despite not having an SRY gene. This is because they have an abnormal amount of androgen receptors given their sex, which can receive enough of the little or big amount of testosterone they make, causing male development.