AP Bio Unit 5: Heredity

Meiosis

Meiosis

a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes

Mitosis

a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.

Sex Cells

Meiosis only happens in these cells

Crossing over

Scrambling genetic information by overlapping chromosomes and exchanging

Haploid

Meiosis reduces the number of chromosome sets from diploid to _______

Gametes

The result of meiosis: sperm or egg

Meiosis I

The first part of MeiosisM

Meiosis II

The second part of Meiosis

Prophase I

Duplicated Homologous Chromosomes pair and exchange segments (cross over) (2n)

Tetrad

During crossing over/synapsis, homologous chromosomes connect to form this

Metaphase I

Chromosomes are arranged at the metaphase plate → 1 pair facing each pole (Diploid)

Anaphase I

Each pair of homologous chromosomes separates

Sister chromatids remain attached to each other

2 Haploid

During Telophase I and cytokinesis, __________ cells form

each half of the cell has a complete set of duplicated chromosomes

Prophase II

Cells are completely split

Cells have a haploid set of duplicated chromosomes

Metaphase II

Chromosomes are positioned at the metaphase plate

2 Sister chromatids are not identical due to crossing over

Anaphase II

 Sister Chromatids Separate

Chromosomes move toward opposite poles

Genetically Distinct

At the end of Meiosis II, during Telophase and cytokinesis, Haploid Daughter cells are formed (gametes), and they are all _________

Half

Gametes have _____ the amount of chromosomes as their parent

Genetic Variation

This contributes to evolution and resilience and would not be possible without Meiosis

Random Fertilization

This makes it impossible to determine which gamete will be fertilized and increases genetic diversity

Nondisjunction

the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

Mendel’s Laws

These laws concern the inheritance of traits and genes

Law of Dominance

2 alleles: some will always be expressed, others only if both are non-dominant (dominant vs recessive)

Law of Segregation

An individual who is heterozygous sometimes passes on the dominant, and sometimes the recessive trait

• Gametes cause only ½ of the genetic information to be passed on

  • 2 of the same allele separate before genetic formation

Independent Assortment

Passing on one allele does not impact passing on another (separate → any combination)

Fertilization

Fusion of 2 haploid gametes → restore diploid number of chromosomes

• New combination of alleles in zygotes increase genetic diversity

• Rules of probability may be applied (expression chance depends on gene frequencies)

  • Pattern of inheritance may often be predicted

Linked Genes

These genes are close together on a chromosome, highly increasing their chances of being passed on together

9:3:3:1

Ratio associated with a dihybrid cross

Incomplete Dominance

Non-Mendelian Genetics

heterozygous phenotype is intermediate between homozygous phenotypes

Multiple Alleles

Non-Mendelian Genetics

existence of several known alleles for a gene (ie blood)

Polygenic

Non-Mendelian Genetics

2 or more genes affect a single phenotypic character (ie skin)

Pleiotropy

Non-Mendelian Genetics 

one gene affects organism in many ways (ie sickle cell anemia)

Chromosomal Theory of Inheritance

This theory states that chromosomes are the vehicles of genetic heredity. Neither Mendelian genetics nor gene linkage is perfectly accurate; instead, chromosome behavior involves segregation, independent assortment, and occasionally, linkage.

Recombination

the process by which DNA strands are broken and repaired, producing new combinations of alleles,

Genotype

Genetic Makeup of an organism

Phenotype

the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Monohybrid

Cross of 2 individuals with homozygous genotypes (GG x gg)

Dihybrid

a cross with 2 hybrids that are heterozygous for alleles of two different genes

Sex-Linked

Genes found on an X or Y Chromosomes

Recombination Frequency

The frequency with which a single chromosomal crossing occurs between two genes during meiosis

Non Nuclear

the inheritance of genetic material not originating from the nucleus of the cell, but from the DNA found in the cytoplasm

No Plasticity

 Environment does not affect phenotype

Plasticity

Environment has some impact on phenotype

Highly Variable Plasticity

Environment has a profound impact on phenotypeS

Selective Pressure

any reason for organisms with certain phenotypes to have either a survival benefit or disadvantage.

Genetic Drift

Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.