AP Bio Unit 6: Heredity (in progress)

Asexual Reproduction

Mitosis, produces exact copies in single-celled or simple multiceullar eukaryotes

Sexual Reproduction

Reproductive cells in reproduction in complex multicelled organisms are produced by meiosis and create variation in offspring.

Meiosis

The type of cell division that creates gametes each with half of your genetic information.

Gametes

Haploid, 23 chromosomes, Egg & sperm cells

Haploids

1N - unpaired chromosomes (ex: gametes)

Diploids

2N - two complete sets of chromosomes, one from each parent (ex: zygotes)

Zygotes

Diploids, 46 chromosomes (23 homologous pairs), when gametes combine

Somatic Cells

Diploid, any cell that’s not reproductive

Homologous Chromosomes

Each chromosome from each parent has a match (homolog) and genes are the same, but alleles can be different.

Humans have __ unique chromosomes, __ in total

23, 46

XX

Female

XY

Male

Meiosis Stages

Meiosis I & Meiosis II

Meiosis I

Starts with 1 cell with 46 chromosome pairs (92 sister chromatids) and ends with 2 haploid cells, each with 23 chromosome pairs (46 sister chromatids).

Meiosis II

Starts with the 2 haploid cells with 23 chromosome pairs each (46 sister chromatids), and ends with 4 haploid cells, each with 23 single chromosomes (23 chromatids).

Genetic Variation

Increases the likelihood that some members of a population will survive (natural selection). Sexual reproduction also increases variation in populations through independent assortment, crossing over, or random fertilization.

Independent Assortment of Chromosomes

Occurs in Meiosis I, where chromosome pairs line up in any order and are sorted independently of one another. This contributes to genetic diversity because each gamete will have a unique combination of chromosomes.

Crossing Over

Occurs in Prophase I, where two chromosomes (one from the mother, one from the father) line up and their parts switch. This contributes to genetic diversity because it will result in a brand new mix of alleles (traits) in the final gametes.

Random Fertilization

Any sperm may randomly fertilize any egg. This contributes to genetic diversity because there are countless unique combinations that can be made.

Oogensis

The process of egg (ovum) formation in females. It occurs in the ovaries and involves meiosis, resulting in one mature egg cell (ovum) and three smaller polar bodies that eventually degenerate.

Spermatogenesis

Spermatogonia (spermatocyte) divide to create four genetically unique haploid sperm from each original spermatogonium.

Errors in Meiosis

Nondisjunction, breaking of chromosomes

Nondisjunction

Problems with the meiotic spindle cause daughter cells to have too many or too few chromosomes (can occur in meiosis I or meiosis II). This can result in trisomies or monosomies, often leading to miscarriage.

Trisomy

Zygotes with 3 copies of a chromosome

Monosomy

Zygotes with 1 copy of a chromosome

Chromosome Maps

• Genes are mapped to chromosomes

• Distance is determined by the frequency of crossover

• Genes closer together or closer to the centromere are less likely to switch positions

• #s on the side = % chance of swtiching

How Deletion Changes Chromosome Structure

Removes a chromosomal segment

How Duplication Changes Chromosome Structure

Repeats a segment

How Inversion Changes Chromosome Structure

Reverses a segment within a chromosome

Translocation

Moves a segment from one chromosome to another nonhomologous one

Gregor Mendel

He documented inheritance in peas and found that traits come in alternate versions, an organism inherits 2 alleles (1 from each parent) for each characteristic, and some traits mask others.

Mendel’s Laws

Law of segregation, Law of Independent Assortment, & Law of Dominance

Mendel’s Laws: Law of Segregation

During meiosis (anaphase I), homologous chromosomes and their alleles separate. Each allele for a trait is packaged into a separate gamete.

Mendel’s Laws: Law of Independent Assortment

Different genes separate into gametes independently because the non-homologous chomrosomes aligned independently during metaphase I. This is only applies for genes on separate chromosomes or on the same chromosome, but far apart.

Mendel’s Laws: Law of Dominance

Hybrid offspring will only inherit the dominant trait in the phenotype. The suppressed alleles are recessive.

Phenotype

The physical appearance of a trait

Genotype

An organism’s genetic makeup

Allele

Different versions of a gene at the same location on homologous chromosomes

Locus

The physical location of an allele on a chromosome

Homozygous

PP or pp

Heterozygous

Pp

Dominant Allele

A functional protein that masks other alleles. If it’s homozygous dominant, 100% of the functional protein is produced. If it’s heterozygous, only 50% of the functional protein is produced.

Recessive Allele

An allele that often makes a malfunctioning protein

Test Cross

Conducted when an organism has the dominant phenotype, but unknown genotype (homozygous dominant or heterzygous?). It’s tested by crossing the organism with one that is homozygous recessive.

Monohybrid Cross

The cross between two individual organisms accounting for only one trait

Dihybrid Cross

The cross between two individual organisms accounting for two traits