Finals Prep Biology: Unit 6 - Classical Genetics

Describe how Gregor Mendel carried out his experiments and what he contributed to the study of genetics

He studied the inheritance of the two variations of each trait seen in pea plants

He found that what he labeled as the P generation was a true-breeding plant and therefore would always produce offspring (F1) with the truebred trait

He noticed that in the F1 generation, one version of the trait would completely vanish and yet reappear in the F2 generation in a 3:1 ratio

He concluded that each plant has two factors for each trait and it inherited one factor from each parent, making him the first to collect data and demonstrate how inheritance of genes worked

Describe the characteristics of a good research organism (pea plant, fruit fly, etc)

They are small, inexpensive, reproduce quickly, and produce many offspring, which makes collecting large amounts of data easier

Identify instances of incomplete dominance, codominance, multiple allele inheritance, polygenic inheritance, and epistasis, and apply these principles to genetic crosses

Incomplete dominance - neither allele is completely masked, so the phenotype appears as a mix of the two homozygous traits

Polygenic inheritance - involves the presence of a wide range of phenotypes (ex. height, hair color, skin tone)

Epistasis - the expression of one gene directly affects the expression of another

Codominance - both alleles are present (spots, stripes)

Describe the process of meiosis, identify what occurs during each stage, and at what stages the cells are diploid and haploid

Cells are diploid until the end of PMAT 1 and are haploid through PMAT 2

Prophase - poles

Metaphase - middle

Anaphase - away/apart

Telophase - two

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Identify how many chromosomes should be found in human somatic (body) cells and human gametes

Human somatic cells - diploid, 2N, 46 total

Human gametes - haploid, N, 23 total

Explain how nondisjunction can happen and why it is harmful

It occurs in anaphase 1 of meiosis and results in a homologous pair of chromosomes not separating, leaving one daughter cell with double the necessary genetic info and one with nothing

Explain how crossing over occurs and how it increases genetic diversity

It occurs during prophase 1 of meiosis when chromosomes line up in tetrads, creating different combinations of alleles in gametes, allowing offspring to be genetically different than there parents and siblings

Describe the advantages and disadvantages of sexual and asexual reproduction

Advantages:

Sexual reproduction - increases the genetic diversity of a population

Asexual reproduction - is able to produce more offspring quicker

Disadvantages:

Sexual - takes longer for the offspring to form

Asexual - little to no variation in offspring

Gene

Passed from one generation to the next

Allele

The different forms of a gene

Genotype

Genetic makeup

Phenotype

Physical traits

Dominant

The allele that can mask the recessive and therefore only requires one to exhibit the trait

Recessive

The allele that can be masked by a dominant allele and therefore requires two to be the exhibited trait

Law of Dominance

Some alleles are dominant, others are recessive

An organism needs one dominant allele or two recessive alleles to exhibit a trait

Law of Independent Assortment

Genes for different traits can segregate independently during gamete formation and therefore do not affect one another

Homozygous

Two identical alleles for a gene

Heterozygous

Two different alleles for a gene

Punnet Square

A visible model that uses mathematic possibility to help predict the genotype and phenotype combinations that will occur from genetic crosses (parents to offspring)

Monohybrid

A type of cross involving only one trait or gene

Dihybrid

A type of cross involving two different traits or genes

Multiple Alleles

Genes that exist in more than two forms (ex. human blood type, rabbit fur color)

Codominance

The phenotypes for both alleles are clearly expressed

Incomplete Dominance

One allele is not completely dominant over another

looks like a mixture of the dom and rec traits

Epistasis

One allele pair influences the behavior of the others

Polygenic Inheritance

Traits that are produced by the interaction of several genes (ex. fruit fly eye color, dog coat color)

Autosomal

Chromosomes that aren't the sex chromosome

Sex-linked (X-linked)

Occurs in only males, but females can be carriers

Is recessive if it skips one or more generations (common)

Pedigree

A record or chart showing the ancestry or lineage of an individual, often used to track family history or genetic trait

Meiosis

The process of cell division that occurs in PMAT1 and PMAT2 with a goal of creating gametes and reducing the number of chromosomes in each daughter cell by half

Homologous Pair

Chromosomes with the same genes, one originally from each parent

Tetrad

A set of 4 chromatids, formed during prophase 1 of meiosis

Crossing Over

A crucial genetic process that occurs during prophase 1 of meiosis, involving the exhchange of genetic material between homologous chromosomes and results in new combinations of genes being passed down, increasing genetic variation

Diploid

Containing both sets of homologous chromosomes (2N)

Haploid

Containing only a single set of chromosomes (N)

Sexual Reproduction

Involves the fusion of two separate parent cells to create genetically unique offspring with some traits from each parent

Asexual Reproduction

A single parent produces genetically identical offspring

Occurs in almost all unicellular organisms and some multicellular organisms, but only by cell division

Nondisjunction

Failure of chromosomes to properly separate during meiosis/mitosis, leading to an abnormal number of chromosomes in the cells produced

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