Chapter 11: Intro to Genetics Study Guide


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Biology Chapter 11: Introduction to Genetics Study Guide


  • Genetics – The scientific study of heredity
  • Fertilization – When the male and female reproductive cells join during sexual reproduction
  • Trait – A specific characteristic (seed color or plant height) which varies from one individual to another
  • True-breeding – Organisms which, if allowed to self pollinate, would produce identical offspring every time.
  • Gene – Chemical factors which determine traits.
  • Allele - one of two or more alternative forms of a gene, occupying the same position locus on paired chromosomes and controlling the same inherited characteristic
  • Segregation – Separation of alleles during the formation of sex cells (gametes). Each parent produces on of each trait.
  • Gametes - a specialized male or female cell with half the normal number of chromosomes that unites with a cell of the opposite sex in the process of sexual reproduction. Ova and spermatozoa are gametes that unite to produce a cell zygote that may develop into an embryo.
  • Dominant – An organism with a dominate allele (1 or 2) will always portray the dominate trait
  • Recessive – An organism without a dominate cell will portray the recessive trait – only pokes through without a recessive trait (used to describe a gene that produces an effect in an organism only when its matching allele is identical. The effect is masked when the matching allele is nonidentical.)
  • Punnett Square – a diagram that is used to predict and compare the genetic variation that will result from a cross
  • Homozygous – organisms with two identical alleles for a certain trait (TT or tt)
  • Heterozygous – organisms with two different alleles for a certain trait (Tt or tt)
  • Phenotype – physical characteristics
  • Genotype – genetic makeup
  • independent assortment – Alleles for different traits segregate independently of those for another trait. Accounts for the variation of genetic info in plants, animals, and other organisms.
  • incomplete dominance – Cases where one allele is not completely dominate over one another and the trait exhibited appears to be somewhere in between the 2 parent phenotypes
  • Codominance – Both alleles contribute to the phenotype. For example white + black = speckled
  • Multiple allele trait - more than 2 possible alleles exist in a population (but still only 2 in one organism)
  • Polygenic trait – Traits controlled by two or more genes

11.1 The Work of Mendel

Describe Mendel’s education and influences: Mendel studies breeding in pea plant. He wanted to figure out the reasons why certain traits showed up in children where both parents do not exhibit the trait.

How did the structure of flowers allow Mendel to perform his experiments. The plants self-fertilization could be disabled, and the plants could be manually cross fertilized by Mendel.

Describe Mendel’s experiments (traits he studied, generations, P, F1, F2 generations, etc.) 7 traits (dominate first):

  • Seed Shape: Round vs Wrinkled
  • Seed Color: Yellow vs Green
  • Seed Coat Color: Gray vs White
  • Pod Shape: Smooth vs Constricted
  • Pod Color: Green vs Yellow
  • Pod Color: Green vs Yellow
  • Flower position: Axial vs Terminal
  • Plant height: Tall vs Short

He first let a population reproduce several times to make sure that it was true-breading (P Generation). He then cross bred plants with different traits (in the same category) with each other. This was the F1 generation. He then crossed some F1 with each other to produce the F2 generation. Some plants (about ¼) in the F2 generation showed traits not exhibited by any plants before them.

Does dominant mean that an allele is more abundant in a population? Explain. No. It only means that when an organism has at least 1 of that gene, the organism will exhibit that trait.

How does segregation explain the F1 cross results? Alleles for each of the traits separate during the formation of sex cells (gametes) randomly. Each plant randomly place one of the 2 alleles into a gamete.

11.2 Probabilities and Punnett squares

What are Punnett squares? – They are ways of explaining the chance that a certain plant will exhibit a certain phenotype or genotype.

11.3 What are Mendel’s Principles

  • Inheritance of biological characteristics is determined by individual units called genes. Genes are passed from parents to their offspring.
  • In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominate and some may be recessive
  • In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed
  • The alleles for different genes usually separate independently of one another