Genetics Since Mendel

1
Genetics Since Mendel
2
I. Independent Assortment
Mendel wondered if alleles segregate
independently. In other words, does the fact that
the plant has a gene to be tall make it more
likely to have a purple flower gene

• A. Monohybrid crosses

• B. Dihybrid crosses

• 1. Mendels 1st crosses using the genes for one
  trait

• 1. Mendels 2nd test, crossing 2 pure plants.
  Plant A had 2 dominant traits over Plant B who
  had homozygous recessive for both traits
• 2. He then crossed the offspring

3
I. Independent Assortment

• C. The heterozygous offspring from the 1st
  crossed showed that the genes for different
  traits segregate independently during gamete
  formation(sperm/egg
• 1. This account for the wide variation between
  organisms of the same species

4
Review Mendels Principles

• 1. Inheritance is determined by individual units
  called genes. Passed on from parent to offspring.
• 2. With traits that have more than 1 form, some
  forms of that gene are dominant while others are
  recessive. (Law of Dominance)
• 3. Sexually reproducing organisms, each
  individual gets a copy from each parent.(Law of
  individual assortment)
• 4. Alleles segregate independently from one
  another (Law of segregation)

5

• Most genes are beyond Mendels work since not all
  genes show simple dominant and recessive alleles.
• Most traits are determined by multiple alleles
  and multiple genes

6
II. Incomplete Dominance

• A. When progeny of 2 homozygous parents show an
  intermediate phenotype this inheritance is called
  incomplete dominance. No allele is completely
  dominant (All Caps for cross)
• 1. Example Red flower plant crossed with a
  White flower plant produced Pink flowered plants

7
III. Codominance

• A. Both alleles contribute to the phenotype, the
  appearance is a speckled animal
• Ex. Ermitte chicken, Roan cow, Geckos, AB Blood

8
IV. Multiple Alleles

• A. Mendel studied traits in pea plants where only
  two alleles controlled them.
• B. Many traits however, are controlled by more
  than 2 alleles and are said to be multiple allele
  that produce more than 3 phenotypes
• 1. Example blood type (IA, IB i)

9
V. Polygenic Inheritance

• A. A trait that is produced by a combination of
  genes is called polygenic inheritance
• 1. Examples Skin color (4 genes), eye color,
  height

10
VI. Linked Genes

• A. Some genes on the same chromosome stay
  together during assortment move as a group.
  This group of genes are considered linked genes
  are usually inherited together.
• 1. The frequency of crossing-over between any 2
  linked alleles is proportional to the distance
  between them.
• Farther apart more likely to separate during
  crossing-over more recombination

11
VII. Genetics the Environment

• A. Characteristics are determined by interaction
  between genes and the environment.
• 1. Temperature can alter how genes can be
  expressed
• 2. Diabetes, heart disease, cancer bipolar
  disorder all have a genetic component with
  environmental influence. (nature vs. nuture)

12

• Dihybrid cross
• In certain bacteria, an oval shape is dominant
  over round and thick cell walls are dominant over
  thin. Cross a heterozygous oval, thick cell
  walled bacteria with a round, thin cell walled
  bacteria. Describe the phenotype of the
  offspring.