Human Genetics
Who do you resemble most? Is it your mom, your dad, a grandparent? Human genetics determines what and who we will look like. The way we inherit traits determines what out outward appearnece will look like. When humans reproduce there are many different ways in which their offspring can inherit traits. Mendel's principles set the basis of the humna genetics. These principles include:

o The inheritance of biological characteristics is determined by individual units known as genes.
o When two or more traits are present, some are dominant and some are recessive.
o Genes are segregated from each other when gametes are formed.
o Alleles from different traits usually segregate independently from each other.

Not all genes show simple patterns of either dominant or recessive alleles.

o Incomplete Dominance- situation in which one allele is not completely dominant over the other.
o Codominance- situation in which both alleles of a gene contribute to the phenotype of the organism.
o Polygenic Traits- traits controlled by two or more genes.
o Multiple Alleles- three or more alleles of the same gene.

Meiosis is formerly defined as the process of reduction division in which the number of homologous chromosomes per cell is cut in half through the seperation of homologous chromosomes in a diploid cell.
Words to know:
- Homologous: chromosomes that each have a corresponding chromosome from the opposite-sex parent.
- Diploid: cell that contains both sets of homologous chromosomes.
- Haploid: cell that contains only a single set of chromosomes.

- Meiosis 1- Stages

o Prophase one- the longest and most complex stage. During this phase the homologous chromosomes come together to form a tetrad. Crossing over occurs, DNA changes.
o Metaphase one- homologous chromosomes line up randomly at the center of the cell, called independent assortment.
o Anaphase one- the homologous chromosomes in the center of the cell divide.
o Telophase one/Cytokinesis- two nuclei form and cytokinesis occurs, resulting in two haploid cells.
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- Meiosis 2- Stages

o Prophase two- very similar to prophase one, except the sister chromatids come together.
o Metaphase two- the sister chromatids line up along the middle of the cell.
o Anaphase two- same occurrences as anaphase one, the sister chromatids separate.
o Telophase two: results in four genetically unique haploid cells.
- Main difference between meiosis one and two:
o Meiosis one contains homologous chromosomes.
o Meiosis two contains sister chromatids.
- Main goal of meiosis is to produce egg and sperm cells.
- Two important things accomplished through meiosis one.
o Chromosome reduction
o Genetic recombination

For More on Meiosis:

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- A karyotype is a snapshot of the chromosomes which allows us to count how many chromosomes we have.

- Male Karyotype: 46 XY

- Female Karyotype: 46 XX

- Disorders include:
o Down Syndrome (Trisomy 21): three copies of chromosome 21
§ 47 XX +21
o Jacob’s Syndrome: extra Y chromosome
§ 47 XYY
o Klinfelter’s Syndrome: extra X chromosome, normal male; tend to be tall and infertile

§ 47 XXY
o Turner Syndrome: only one X chromosome, 10 percent of miscarriages have this abnormality
§ 45 X

For more on Karyptyping:

- Pedigrees: when deciding where you get your genes from, pedigrees help show the relationships of family members based on their traits and patterns of inheritance.
o Pedigree: chart which show the relationships between families.
o Shows how people inherit traits based on the traits of family members.
- Autosomal Recessive- recessive trait that can skip a generation.

For more on Pedigrees:

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