UNIT 5: HEREDITY

Sexual Reproduction

involves two parents, creating offspring with unique genetic combinations (requires fertilization)

Fertilization

the union of haploid gametes (sperm and egg)

What does fertilized egg lead to?

diploid zygote

Somatic cells

somatic (body cells) made through mitosis are diploid (2n), meaning they have two of each chromosome from each parent

Homologous Chromosomes

chromosome pairs that are similar in length, shape, and gene content but may have different variations

Gamete

sperm and egg; haploid (n), containing a single set of chromosomes

How many gametes do humans have?

23 haploid cells

What is the only type of human cell produced by meiosis?

gametes are the only types of human cells produced by meiosis

How do gametes form?

they are made at sexual maturity from germ cells in the ovaries and testes

Interphase

similar to mitosis; DNA replicates during S phase (only happens before Meiosis I)

Meiosis I, Prophase I

chromatin condenses into chromosomes, nuclear membrane degrades, centrioles move towards opposite poles, spindle fibers form

Synapsis

homologous chromosomes pair up to form tetrads

What increases genetic variation during prophase I?

crossing over occurs (nonsister chromatids exchange DNA segments), resulting in genetic recombination of traits and increases genetic diversity

Chiasmata

X-shaped regions where crossing over occurs (tetrad has 1 or more)

Metaphase I

homologous chromosomes align at the metaphase plate

What leads to genetic variation during Metaphase I?

leads to Independent Assortment, increasing genetic variation; sister chromatids remain together

Anaphase I

proteins responsible for attachment (cohesin) breakdown and homologous chromosomes separate and move to opposite poles

Telophase I & Cytokinesis

nuclear membranes form at each pole, spindle degrades, Cytokinesis splits cell into two haploid cells

What happens by the end of Meiosis I

increase in genetic diversity and # of chromosomes are reduced in half (diploid to haploid)

Prophase II

nuclear membrane breaks down, spindle reforms

Metaphase II

chromosomes align in a single file at the metaphase plate, where independent assortment occurs again

Anaphase II

sister chromatids separate and move to opposite poles

Telophase II & Cytokinesis

nuclei form, chromosomes decondense, and cells split

What is produced by the end of meiosis?

produces four genetically unique haploid cells from each parent

What is produced by the end of mitosis?

produces two genetically identical diploid cells w/ the same # of chromosomes and 2 of each just like parent cell

Random Fertilization

any sperm can fuse with any ovum (unfertilized egg)

Karyotype

an image of an individual’s complete set of chromosomes and used to identify chromosomal abnormalities

Nondisjunction

failure of homologous pairs (meiosis I) or sister chromatids (meiosis II) to separate properly, resulting in gametes with extra or missing chromosomes

Aneuploidy

common in humans, where offspring with this condition have an abnormal number of particular chromosome

Trisomy

three copies of a chromosome (down syndrome and edward’s syndrome)

Aneuploidy of Sex Chromosomes

nondisjunction of sex chromosomes

Klinefelter Syndrome

extra chromosome in a male, producing XXY individuals

Monosomy X (Turner Syndrome)

produces X0 females, viable monosomy in humans

Polyploidy

a condition in which an organism has more than two homologous chromosome sets (common in plants, but not animals and humans)

Chromosomal Mutations

mutations in meiosis (unequal crossing over) or mitosis (leads to chromosome breakages), leading to changes in chromosome structure